**2. Basics of symmetric supercapacitors (SSCs)**

have excellent recyclability, typically >5000 times [5]. The past decade has witnessed significant progresses in SCs researches, many types of SCs have come to existence, including but not limited to electrochemical double-layer capacitors (EDLCs) and asymmetric supercapacitors (ASSCs), and they can be further sorted by applicable electrolytes (mainly three types electrolytes: aqueous, organic, and ionic liquid electrolytes) [2]. Still, they are not satisfactory enough from the perspectives of energy stored, which is mainly due to low capacitances or narrow potential windows especially in aqueous electrolytes [6, 7]. Coupling SCs with pseudo-capacitive electrode materials such as transition metal-based materials or electronically conductive polymers is feasible to enlarge the specific energy; however, the lifetime of pseudo-capacitors normally goes down quickly in a few hundred cycles [8, 9]. Currently, it is still very hard to simultaneously obtain large capacitance, high-operating voltage, and high-cycling stability.

118 Supercapacitors - Theoretical and Practical Solutions

Symmetric supercapacitors (SSCs), mainly including carbon-based EDLCs and a few SSCs with identical metallic component- or conductive polymer-based electrodes, supply much higher specific power and cycling stability than pseudo-capacitors, due to the interfacial charging/ discharging mechanism [2, 10]. Their energy are given by the equation (1), in which E is the energy stored in capacitor cell, CT is the total capacitance, and V is the operating voltage. E is proportional to total capacitance and square voltage, which means that specific energy E can be improved via two ways: increasing specific capacitance and expanding operating voltage [11]. Both of these aforementioned two aspects are highly related to the interfacial chemistry and phenomenon [5]. According to the electrochemical double-layer phenomenon established by Helmholtz, the electrochemical interface consists of electrode surface and thin layered electrolyte (containing ions or cations) adjacent to electrode surface. In the first place, this thin layer of electrolyte plays the fundamental roles of conducting ions and facilitating charge compensation on electrode interface; additionally, they can be decomposed or transformed to supply non-Faradaic current once charge transfer occurs when the electrons arrive in or depart from the conduction band of electrode [6]. Before that, electrolyte ions and molecules are forced to strongly absorb onto electrode surface to form a tightly packed stern layer [6, 7]. According to previous literatures, the efficiency and strength of absorption are highly depend on the surface properties of electrode materials, doping, defect, and functionality and can significantly alter the interactions between electrolyte and electrode interface [11–13]. Therefore, in order to achieve high operating voltage as well as high energy, it is critical to address the interface issues regarding both the surface properties of electrode materials and the applicable electrolytes.

E = 1/2CTV2 (1)

In the past few decades, many review articles have discussed the investigations on materials selections and device fabrications for developing high-performance SCs, but few accounted for the interface designing and engineering. Also, research progresses from different angles (material synthesis, electrolyte selections, and device fabrications) have come to the point calling for a generic summary for improving the integrated performance of SCs on the clear understanding of electrode interfacial phenomenon. This chapter aims to present and discuss a number of relevant issues, including fundamentals of interfacial (mainly electric double layer (EDL)) capacitance, nanoscale charge transfer, discussions on a few benchmarked Symmetric supercapacitors (SSCs) are mainly built on electrochemical double-layer configured identical positive and negative electrodes; most applicable electrode materials are carbon-based due to their high chemical stability of carbon materials [1, 14]. The electrochemical doublelayer model, first established by Helmholtz, reveals that two oppositely charged ionic layers are formed at electrode-electrolyte interfaces under electrochemical forces driven. Afterward, Stern recognized that there are two regions of ion distribution at the electrode-electrolyte interfaces: one inner layer and one outer layer, as schematically depicted in **Scheme 1**. The inner region, where ions are strongly absorbed onto the electrode surface, is called the compact layer (or Stern layer); and the outer layer consists of a continuous distribution of ions in solution [10]. The capacitance at electrode-electrolyte interface (CEDL) with electrochemical double-layer configuration can be divided into capacitance from the inner compact layer (CH) and capacitance from the diffuse layer (CDiff), as described in equation (2)

$$\frac{1}{\overline{C}\_{\text{LTM}}} = \frac{1}{\overline{C}\_{\text{H}}} + \frac{1}{\overline{C}\_{\text{Dgf}}} \tag{2}$$

There are several critical factors that give significant impact on CEDL, mainly including the conductivity of electrode material, the surface area of electrode materials, the accessibility to the inner electrochemical surface, the electric field across the electrode, and the electrolyte/solvent properties [15]. For instance, SCs with high-surface area porous carbon electrode materials (such as activated carbon) can store much more capacitances by several orders of magnitude. There are also a few other ways that are feasible to enlarge the capacitances including doping heteroatom elements and compositing stable metal oxides or conductive polymers [11, 16]. Heteroatom doping is able to break down the high symmetry of graphitic carbon, creating a large amount of defects, leading to the easy formation of compact inner absorption layer [16]. The advantages of using stable metal oxides or conductive polymers as electrochemical interfaces instead of carbon materials are obvious; they are capable of supplying much more capacitance through pseudo-capacitive absorption besides the EDL capacitance [17]. However, the greatly enlarged capacitances are often obtained on the basis of compromising the efficiency and cycling stability, and only a minor few metal oxides and conductive polymers are qualified due to conductivity and cost issues, which we will summarize later in Section 3.

Besides the electrode materials selection, it is also important to choose a proper electrolyte and solvent to form a robust electrode-electrolyte interface since energy stored in a SSCs

used in SSCs due to their abundant sources, low costs, high porosity, excellent chemical stability, and conductivity [1, 13]. Considering the mechanism of energy stored in a SSC to be mainly dominated by electrical double-layer configurations, the overall performance of full SSCs is restricted below this value. Therefore, exploring high-performance electrode materials is urgent in order to achieve high-energy SSCs. There are mainly two types of commonly used materials: carbon-based materials and pseudo-capacitive materials, which we will sepa-

Toward High-Voltage/Energy Symmetric Supercapacitors via Interface Engineering

http://dx.doi.org/10.5772/intechopen.73131

121

As mentioned in Section 2, EDL-configured SCs are mainly based on various kinds of carbon materials such as activated carbon (AC). In this specific part, the general ways of enlarging capacitance of carbon-based materials are first summarized via giving representative example. Generally speaking, three ways can be utilized to achieve these goals: (1) increasing the electrochemically accessible surface area (EASA), (2) creating more anchoring sites for charge carriers, and (3) involving few amounts of pseudo-capacitance on the basis of EDL capacitance [4, 15, 24]. As followed, we will give explanations on the latter two strategies; the foremost strategy of enlarging EASA is only for listing because it involves a very few interfacial

The charming feature of carbon materials is mostly founded on the largely conjugated aromatic six-atom ringed carbon that create huge amount of delocalized electrons, for instance, graphene, one typical allotrope of carbon, have an ultrahigh charge carrier mobility of

sically generates highly symmetric molecular structure. The superlarge conjugation system, on one hand, enables fast transportation of charge carriers and, on the other hand, leaves very few sites for ions to absorb. From this specific aspect, doping heteroatom species and creating defects in graphitic carbon lattice can significantly boost the apparent capacitance by providing more sites for ions anchoring, as depicted in **Scheme 2** [26]. In some cases, very strong chemical binding on heavily doped carbon sites can even generate charge transfer to achieve much larger capacitance [16, 27]. Therefore, if let a small proportion of conductivity sacrificed, desirably larger capacitances can be obtained via simply involving more heteroatom sites

Activated carbons (AC) are the most commonly used electrode materials in SSCs because of their large surface areas and low costs. ACs are usually converted from carbon-rich chemicals and biomasses under the high-temperature activation of chemicals such as KOH, ZnCl2

 [28, 29]. Although, very high porosity is obtained, most of the heteroatom-containing functionalities and moieties are forced to be removed by the disturbance of high temperature [30]. The as-formed clean carbon surface may probably leave very limited sites that are readily to absorb ions, so the most obtainable capacitance using AC electrode materials are falling in 100–200 F g−1. Thanks to the abundant chemistry of carbon species, most of inorganic elements can connect with carbon to break the symmetry of π-π conjugation and also to include partial pseudo-capacitive sites for higher capacitance [11]. For instance, a nitrogen-doped porous carbon (N content ~ 12 at.%) reported by Huang et al. delivered an ultrahigh capacitance of 855 F g−1 and a high specific energy of 41 Wh kg−1 in aqueous electrolytes. The improvement

, and

v−1 s−1 [25]. Meanwhile, the large conjugation system of graphitized carbon intrin-

rately describe in the following paragraphs.

especially containing nitrogen species [11].

chemistries, which is not our main topic here in this chapter.

**3.1. Carbon-based materials**

200,000 cm2

H3 PO4

**Scheme 1.** Schematic representations of the cross-sectional EDL structure of electrode/electrolyte interface.

device is governed by the square of operating voltage multiplying capacitance, as described in equation (1). Relative to capacitance, operating voltage actually gives bigger impact on the specific energy of the whole SSCs device. Therefore, pushing the operating voltage to the limit by means of choosing proper electrolyte solution is of significant practical meanings, a robust electrode-electrolyte interface can efficiently prevent the nanoscale charge transfer at the interfaces, thus to largely expand the applicable operating voltage and to enhance the specific energy [6]. In general, electrode-electrolyte interfaces formed in ionic liquid are more stable than in organic solvents, and then in aqueous solution, which is governed by the chemical stable window of solvents [6]. Typically, the chemical stability of the abovementioned three types of electrolytes follows the sequence of ionic liquid > organic electrolyte > aqueous electrolyte. For instance, an ionic liquid electrolyte can deliver a potential window as wide as 4.0 V, while aqueous electrolyte can only supply a 1.23-V wide potential window due to water splitting at 1.23 V [18, 19]. However, in some aqueous cases, by suppressing the activity of water splitting such as in neutral electrolytes, the safe operating voltage can be largely expanded to 1.8 V [20, 21]. The operating voltage can be further enlarged by applying electrode material that has much less activity toward water splitting, leading to a 2.0-V safe operating voltage, which is clearly achieved by mediating the interface properties [22]. The discussion on interface engineering for safe voltage expansion is placed in Section 4.

#### **3. High-capacitance electrode materials for SSCs**

Symmetric supercapacitors (SSCs), as one typical sort of SCs, though are able to provide charging/discharging in several minutes, deliver incomparable capacitance as to secondary batteries (such as Li-ion battery) [23]. Therefore, it is crucial to enlarge the specific energy stored in each electrode by either optimizing existed electrode materials or developing new types of materials. For now, carbon-based materials contribute to most of electrode materials used in SSCs due to their abundant sources, low costs, high porosity, excellent chemical stability, and conductivity [1, 13]. Considering the mechanism of energy stored in a SSC to be mainly dominated by electrical double-layer configurations, the overall performance of full SSCs is restricted below this value. Therefore, exploring high-performance electrode materials is urgent in order to achieve high-energy SSCs. There are mainly two types of commonly used materials: carbon-based materials and pseudo-capacitive materials, which we will separately describe in the following paragraphs.

#### **3.1. Carbon-based materials**

device is governed by the square of operating voltage multiplying capacitance, as described in equation (1). Relative to capacitance, operating voltage actually gives bigger impact on the specific energy of the whole SSCs device. Therefore, pushing the operating voltage to the limit by means of choosing proper electrolyte solution is of significant practical meanings, a robust electrode-electrolyte interface can efficiently prevent the nanoscale charge transfer at the interfaces, thus to largely expand the applicable operating voltage and to enhance the specific energy [6]. In general, electrode-electrolyte interfaces formed in ionic liquid are more stable than in organic solvents, and then in aqueous solution, which is governed by the chemical stable window of solvents [6]. Typically, the chemical stability of the abovementioned three types of electrolytes follows the sequence of ionic liquid > organic electrolyte > aqueous electrolyte. For instance, an ionic liquid electrolyte can deliver a potential window as wide as 4.0 V, while aqueous electrolyte can only supply a 1.23-V wide potential window due to water splitting at 1.23 V [18, 19]. However, in some aqueous cases, by suppressing the activity of water splitting such as in neutral electrolytes, the safe operating voltage can be largely expanded to 1.8 V [20, 21]. The operating voltage can be further enlarged by applying electrode material that has much less activity toward water splitting, leading to a 2.0-V safe operating voltage, which is clearly achieved by mediating the interface properties [22]. The discussion on interface engineering for safe voltage expansion is

**Scheme 1.** Schematic representations of the cross-sectional EDL structure of electrode/electrolyte interface.

Symmetric supercapacitors (SSCs), as one typical sort of SCs, though are able to provide charging/discharging in several minutes, deliver incomparable capacitance as to secondary batteries (such as Li-ion battery) [23]. Therefore, it is crucial to enlarge the specific energy stored in each electrode by either optimizing existed electrode materials or developing new types of materials. For now, carbon-based materials contribute to most of electrode materials

placed in Section 4.

120 Supercapacitors - Theoretical and Practical Solutions

**3. High-capacitance electrode materials for SSCs**

As mentioned in Section 2, EDL-configured SCs are mainly based on various kinds of carbon materials such as activated carbon (AC). In this specific part, the general ways of enlarging capacitance of carbon-based materials are first summarized via giving representative example. Generally speaking, three ways can be utilized to achieve these goals: (1) increasing the electrochemically accessible surface area (EASA), (2) creating more anchoring sites for charge carriers, and (3) involving few amounts of pseudo-capacitance on the basis of EDL capacitance [4, 15, 24]. As followed, we will give explanations on the latter two strategies; the foremost strategy of enlarging EASA is only for listing because it involves a very few interfacial chemistries, which is not our main topic here in this chapter.

The charming feature of carbon materials is mostly founded on the largely conjugated aromatic six-atom ringed carbon that create huge amount of delocalized electrons, for instance, graphene, one typical allotrope of carbon, have an ultrahigh charge carrier mobility of 200,000 cm2 v−1 s−1 [25]. Meanwhile, the large conjugation system of graphitized carbon intrinsically generates highly symmetric molecular structure. The superlarge conjugation system, on one hand, enables fast transportation of charge carriers and, on the other hand, leaves very few sites for ions to absorb. From this specific aspect, doping heteroatom species and creating defects in graphitic carbon lattice can significantly boost the apparent capacitance by providing more sites for ions anchoring, as depicted in **Scheme 2** [26]. In some cases, very strong chemical binding on heavily doped carbon sites can even generate charge transfer to achieve much larger capacitance [16, 27]. Therefore, if let a small proportion of conductivity sacrificed, desirably larger capacitances can be obtained via simply involving more heteroatom sites especially containing nitrogen species [11].

Activated carbons (AC) are the most commonly used electrode materials in SSCs because of their large surface areas and low costs. ACs are usually converted from carbon-rich chemicals and biomasses under the high-temperature activation of chemicals such as KOH, ZnCl2 , and H3 PO4 [28, 29]. Although, very high porosity is obtained, most of the heteroatom-containing functionalities and moieties are forced to be removed by the disturbance of high temperature [30]. The as-formed clean carbon surface may probably leave very limited sites that are readily to absorb ions, so the most obtainable capacitance using AC electrode materials are falling in 100–200 F g−1. Thanks to the abundant chemistry of carbon species, most of inorganic elements can connect with carbon to break the symmetry of π-π conjugation and also to include partial pseudo-capacitive sites for higher capacitance [11]. For instance, a nitrogen-doped porous carbon (N content ~ 12 at.%) reported by Huang et al. delivered an ultrahigh capacitance of 855 F g−1 and a high specific energy of 41 Wh kg−1 in aqueous electrolytes. The improvement

**3.2. Interfacial pseudo-capacitive materials**

*3.2.1. Electronically conducting polymers (ECPs)*

*CP* → *CPn*+ (*A*−)

*CP* + *n e*− → (*C*+)

).

PEDOT is poly (3,4-ethylenedioxythiophene).

**Table 1.** Theoretical specific capacitance of conducting polymers.

of square voltage (V2

**Conducting polymer**

good rate/cycling performance.

Pseudo-capacitance is achieved by Faradaic electron charge-transfer with redox reactions, intercalation or electro-sorption. Unlike electrochemical double-layer supercapacitor, pseudosupercapacitor use electronically conducting polymers (ECPs) or stable metal oxides electrodes can achieve balanced capacitive performance of much enhanced capacitance and fairly

Toward High-Voltage/Energy Symmetric Supercapacitors via Interface Engineering

http://dx.doi.org/10.5772/intechopen.73131

123

ECPs are one typical sort of pseudo-capacitive materials that can engage electrochemical doping or redox reaction with anions and cations, many ECPs such as polyaniline (PANI), polypyrrole (PPy), and derivatives of polythiophene (PTh) have been widely applied in supercapacitors due to their large capacitances, flexibility, and low costs. The typical dopant level for these polymers as well as typical specific capacitances and applicable voltage ranges are given in **Table 1**. The mechanism of ECPs storing charges can be described by the follow-

ECPs-made SSCs can be sorted into two categories: Type I-using the same *p*-doped ECPs for both electrodes and Type II-using the same ECPs but using different forms of ECPs as electrodes (*p*-doped form as positive electrode and *n*-doped form as negative electrode). When the Type I SSCs is charged, the positive electrode is completely oxidized while the negative electrode remains neutral, which supplies 0.5–0.75 V potential difference. When it is discharged, both electrodes are semi-oxidized, which makes only 50% of the *p*-doped capacitance can be used. In addition, the supplied potential of Type II SSCs is higher compared with Type I SSCs. This improvement would result in high specific energy due to much larger difference

**Mw (g mol−1) Conductivity (S cm−1) Dopant level Potential range (V) Theoretical specific**

Mw is molecular weight per unit monomer (g mol−1) PANI is polyaniline, PPy is polypyrrole, PTh is polythiophene and

*n* + *n e*− (*p* − *doping*) (3)

*n CPn*− (*n* − *doping*) (4)

**capacitance (F g−1)**

ing two formulas, *i.e*., *p*-doping upon oxidization and *n*-doping upon reduction.

**PANI** 93 0.01–5 0.5 0.7 750 **PPy** 67 0.3–100 0.33 0.8 620 **PTh** 84 2–150 0.33 0.8 485 **PEDOT** 142 300–500 0.33 1.2 210

**Scheme 2.** Aromatic carbon lattices can embrace many types of heteroatom doping such as nitrogen (blue), oxygen (green), sulfur (pink), and so on. Defective carbon sites (red) that are unsaturated can also be treated as anchoring sites for ions.

mostly originates from robust redox reactions at electrochemically active nitrogen-containing sites that transform inert graphene-like layered carbon [16]. A nitrogen, sulfur-co-doped carbon fabricated by Sun et al. exhibited a very high specific capacitance of 427 F g−1 at 1.0 A g−1 and still showed an excellent capacitance of 270 F g−1 at superhigh current density of 100 A g−1 (**Figure 1**) [31]. However, the dopant content shall be controlled under an optimistic level; otherwise, the capacitance will not be increased because of severely damaged conductivity. For instance, Cheng et al. fabricated a high level of N, S, or B doping graphene, also called superdoping, achieving 29.82, 17.55, and 10.79 at% for N-, S-, and B-doping, respectively [32]. However, the 29.82 at%-N-doped graphene achieved a medium specific capacitance of 354 F g−1 while the pristine graphene without any doping obtained a specific capacitance of 213 F g−1 (taking 60% of heavily N-doped graphene).

**Figure 1.** (a) SEM image and (b) XPS survey of NS-co-doped carbon materials. (c) Gravimetric capacitance of NS-co-doped carbon materials made SSCs in three aqueous electrolytes. Adapted with permission [31]. Copyright 2017, American Chemical Society.

#### **3.2. Interfacial pseudo-capacitive materials**

Pseudo-capacitance is achieved by Faradaic electron charge-transfer with redox reactions, intercalation or electro-sorption. Unlike electrochemical double-layer supercapacitor, pseudosupercapacitor use electronically conducting polymers (ECPs) or stable metal oxides electrodes can achieve balanced capacitive performance of much enhanced capacitance and fairly good rate/cycling performance.

#### *3.2.1. Electronically conducting polymers (ECPs)*

mostly originates from robust redox reactions at electrochemically active nitrogen-containing sites that transform inert graphene-like layered carbon [16]. A nitrogen, sulfur-co-doped carbon fabricated by Sun et al. exhibited a very high specific capacitance of 427 F g−1 at 1.0 A g−1 and still showed an excellent capacitance of 270 F g−1 at superhigh current density of 100 A g−1 (**Figure 1**) [31]. However, the dopant content shall be controlled under an optimistic level; otherwise, the capacitance will not be increased because of severely damaged conductivity. For instance, Cheng et al. fabricated a high level of N, S, or B doping graphene, also called superdoping, achieving 29.82, 17.55, and 10.79 at% for N-, S-, and B-doping, respectively [32]. However, the 29.82 at%-N-doped graphene achieved a medium specific capacitance of 354 F g−1 while the pristine graphene without any doping obtained a specific capacitance of 213 F g−1

**Scheme 2.** Aromatic carbon lattices can embrace many types of heteroatom doping such as nitrogen (blue), oxygen (green), sulfur (pink), and so on. Defective carbon sites (red) that are unsaturated can also be treated as anchoring sites for ions.

**Figure 1.** (a) SEM image and (b) XPS survey of NS-co-doped carbon materials. (c) Gravimetric capacitance of NS-co-doped carbon materials made SSCs in three aqueous electrolytes. Adapted with permission [31]. Copyright 2017, American

(taking 60% of heavily N-doped graphene).

122 Supercapacitors - Theoretical and Practical Solutions

Chemical Society.

ECPs are one typical sort of pseudo-capacitive materials that can engage electrochemical doping or redox reaction with anions and cations, many ECPs such as polyaniline (PANI), polypyrrole (PPy), and derivatives of polythiophene (PTh) have been widely applied in supercapacitors due to their large capacitances, flexibility, and low costs. The typical dopant level for these polymers as well as typical specific capacitances and applicable voltage ranges are given in **Table 1**. The mechanism of ECPs storing charges can be described by the following two formulas, *i.e*., *p*-doping upon oxidization and *n*-doping upon reduction.

$$\text{CP} \rightarrow \text{CP}^{\bullet+} \left( A^{-} \right)\_{\text{\tiny n}} \star n \, e^{-} \text{ (\$p-doping)}\tag{3}$$

$$\text{CP} + n \, e^- \to \left(\text{C}^\*\right)\_n \text{CP}^{n-} \text{ ( $n-d$ oping)}\tag{4}$$

ECPs-made SSCs can be sorted into two categories: Type I-using the same *p*-doped ECPs for both electrodes and Type II-using the same ECPs but using different forms of ECPs as electrodes (*p*-doped form as positive electrode and *n*-doped form as negative electrode). When the Type I SSCs is charged, the positive electrode is completely oxidized while the negative electrode remains neutral, which supplies 0.5–0.75 V potential difference. When it is discharged, both electrodes are semi-oxidized, which makes only 50% of the *p*-doped capacitance can be used. In addition, the supplied potential of Type II SSCs is higher compared with Type I SSCs. This improvement would result in high specific energy due to much larger difference of square voltage (V2 ).

Mw is molecular weight per unit monomer (g mol−1) PANI is polyaniline, PPy is polypyrrole, PTh is polythiophene and PEDOT is poly (3,4-ethylenedioxythiophene).

**Table 1.** Theoretical specific capacitance of conducting polymers.

Many ECPs such as PANI and PPy can only be *p*-doped due to the very negative potentials required for *n*-doping, if compared with the reduction potential limit of molecular solvent-based electrolytes. For instance, Pan et al. synthesized PANI hydrogel with high surface area and threedimensional porous nanostructures and demonstrated that the as-obtained PANI-based supercapacitor could supply a very large specific capacitance of 480 F g−1, excellent rate capability, and very good cycling stability of 83% capacitance retention after 10,000 cycles but only provide a safe operating voltage of 0.8 V for SSCs. Unique three-dimensional (3D) microstructure by interconnected polymer (**Figure 2**) by Yu et al. exhibit good mechanical properties and high rate performance with specific capacitance of 400 F g−1, excellent rate capability [33]. On the contrary, PTh and its derivatives can be used as *n*-doped ECPs; however, the conductivity of these ECPs after *n*-doping is not very high in the reduced state and thus leads to a low capacitance in the negative potential region [34]. For example, Stenger-smith et al. developed poly (3,4-propylenedioxythiophene) and poly(3,4-ethylenedioxythiophene) as electrode couples show good cycle life [35].

reversible redox reaction, and long cycling life. For instance, RuO2

The main mechanism of the pseudo-capacitive energy storage in MnO2

electrolytes [39, 41]. These can be expressed by the following formula:

represents the protons and alkali metal cations (Li+

high flexibility, and high electrical conductivity [45].

**4. Electrolyte-mediated operating voltage**

ible intercalation/de-intercalation of protons or an adsorption of cations such as Li+

environmental friendliness, and high theoretical capacitances (up to 1100–1300 F g−1) [38–40].

*Mn O*2 + *X*+ + *e*− ↔ *MnOOX* (5)

and coworkers believed that the pseudo-capacitances are mainly occurring in the interfaces due to the difficulty of the protons or cations transportation into the bulk phase materials [38, 42–44].

Usually, the specific capacitance can be improved by tuning morphology, surface area, and porous structure of active material. The most common electrode materials are carbon materials, metal oxides, and ECPs. To maximize the advantages of these materials, composite materials are of great technological advantages due to the combination of the intrinsic properties of each component as well as the synergistic effect resulting from the hybrids. The composites of carbon materials with other materials such as ECPs and metal oxides, which often use carbon materials as substrate, for example, carbon nanotubes, carbon fibers, graphene materials, activated carbon, etc. As depicted in Section 3.2, ECPs and metal oxides are highly promising active electrode materials but these materials suffer from severe cycling stability problems because of the structure collapse caused by swelling and shrinking during charging/discharging. Hybridizing carbon materials with ECPs and/or metal oxides can synergistically boost nearly all the aspects of capacitive performance including conductivity, capacitance, and cycling stability. For instance, Peng et al. fabricated hollow fiber electrodes using reduced graphene oxide (RGO)/ECPs, simultaneously achieving large areal capacitance (304.5 mF cm−2),

Electrolyte is one of the key components of SCs, basically, conveying ionic current and leading the formation of electrical double layer, more importantly, under certain circumstances of matched electrode materials and electrolytes, and facilitating reversible redox processes for larger amount of charges stored in the interfaces. In general, electrolytes used in SSCs can be sorted into two main categories: liquid electrolytes and solid/quasi-solid state electrolytes. Liquid electrolytes can be further sorted into three groups: aqueous electrolytes, organic electrolytes, and ionic liquids (ILs), while solid/quasi-solid state electrolytes can be divided into organic electrolytes and inorganic electrolytes [7]. There is no once-for-all solution for electrolyte selection, each electrolyte has its own advantages and disadvantages. For

voltage of 0.7 V in SSCs [37]. Due to the very high costs, RuO2

military application. While MnO2

where X+

*3.2.3. Composites materials*

can supply a safe operating

125

is attributed to a revers-

) in the electrolyte. Toupin

, Na+ , K+ from

is often limited in aerospace and

http://dx.doi.org/10.5772/intechopen.73131

is generally studied because of their low cost, low toxicity,

Toward High-Voltage/Energy Symmetric Supercapacitors via Interface Engineering

, Na+ , K+

#### *3.2.2. Transition metal oxides*

Transition metal oxides show high pseudo-capacitive behavior with redox chemistry both on and in the interfaces, which have been extensively studied due to high specific capacitance. There are several commonly studied stable metal oxide materials such as RuO2 (theoretical specific capacitance ~ 1000 F g−1) and MnO2 (theoretical specific capacitance: 1100–1300 F g−1) [36]. RuO2 is one of the most explored electrode materials due to the high specific pseudo-capacitance,

**Figure 2.** (a) Illustration depicting controlled synthesis of the CuPcTs doped PPy hydrogel. (b) SEM images of nanostructured PPy hydrogel. (c) Specific capacitance as a function of current density for CuPcTs-PPy and pristine PPy. Adapted with permission [31]. Copyright 2017, American Chemical Society.

reversible redox reaction, and long cycling life. For instance, RuO2 can supply a safe operating voltage of 0.7 V in SSCs [37]. Due to the very high costs, RuO2 is often limited in aerospace and military application. While MnO2 is generally studied because of their low cost, low toxicity, environmental friendliness, and high theoretical capacitances (up to 1100–1300 F g−1) [38–40]. The main mechanism of the pseudo-capacitive energy storage in MnO2 is attributed to a reversible intercalation/de-intercalation of protons or an adsorption of cations such as Li+ , Na+ , K+ from electrolytes [39, 41]. These can be expressed by the following formula:

$$Mn\text{ }O\_2 + X^\* + e^- \leftrightarrow Mn\text{ }OOX\tag{5}$$

where X+ represents the protons and alkali metal cations (Li+ , Na+ , K+ ) in the electrolyte. Toupin and coworkers believed that the pseudo-capacitances are mainly occurring in the interfaces due to the difficulty of the protons or cations transportation into the bulk phase materials [38, 42–44].

#### *3.2.3. Composites materials*

Many ECPs such as PANI and PPy can only be *p*-doped due to the very negative potentials required for *n*-doping, if compared with the reduction potential limit of molecular solvent-based electrolytes. For instance, Pan et al. synthesized PANI hydrogel with high surface area and threedimensional porous nanostructures and demonstrated that the as-obtained PANI-based supercapacitor could supply a very large specific capacitance of 480 F g−1, excellent rate capability, and very good cycling stability of 83% capacitance retention after 10,000 cycles but only provide a safe operating voltage of 0.8 V for SSCs. Unique three-dimensional (3D) microstructure by interconnected polymer (**Figure 2**) by Yu et al. exhibit good mechanical properties and high rate performance with specific capacitance of 400 F g−1, excellent rate capability [33]. On the contrary, PTh and its derivatives can be used as *n*-doped ECPs; however, the conductivity of these ECPs after *n*-doping is not very high in the reduced state and thus leads to a low capacitance in the negative potential region [34]. For example, Stenger-smith et al. developed poly (3,4-propylenedioxythiophene) and poly(3,4-ethylenedioxythiophene) as electrode couples show good cycle life [35].

Transition metal oxides show high pseudo-capacitive behavior with redox chemistry both on and in the interfaces, which have been extensively studied due to high specific capacitance.

**Figure 2.** (a) Illustration depicting controlled synthesis of the CuPcTs doped PPy hydrogel. (b) SEM images of nanostructured PPy hydrogel. (c) Specific capacitance as a function of current density for CuPcTs-PPy and pristine PPy.

Adapted with permission [31]. Copyright 2017, American Chemical Society.

is one of the most explored electrode materials due to the high specific pseudo-capacitance,

(theoretical spe-

(theoretical specific capacitance: 1100–1300 F g−1) [36].

There are several commonly studied stable metal oxide materials such as RuO2

*3.2.2. Transition metal oxides*

124 Supercapacitors - Theoretical and Practical Solutions

RuO2

cific capacitance ~ 1000 F g−1) and MnO2

Usually, the specific capacitance can be improved by tuning morphology, surface area, and porous structure of active material. The most common electrode materials are carbon materials, metal oxides, and ECPs. To maximize the advantages of these materials, composite materials are of great technological advantages due to the combination of the intrinsic properties of each component as well as the synergistic effect resulting from the hybrids. The composites of carbon materials with other materials such as ECPs and metal oxides, which often use carbon materials as substrate, for example, carbon nanotubes, carbon fibers, graphene materials, activated carbon, etc. As depicted in Section 3.2, ECPs and metal oxides are highly promising active electrode materials but these materials suffer from severe cycling stability problems because of the structure collapse caused by swelling and shrinking during charging/discharging. Hybridizing carbon materials with ECPs and/or metal oxides can synergistically boost nearly all the aspects of capacitive performance including conductivity, capacitance, and cycling stability. For instance, Peng et al. fabricated hollow fiber electrodes using reduced graphene oxide (RGO)/ECPs, simultaneously achieving large areal capacitance (304.5 mF cm−2), high flexibility, and high electrical conductivity [45].


**Acknowledgements**

Dr. Gabriel Sarti Lopes and Dr. Jorge E. Moreira of University of São Paulo, FMRP/ USP and Dra. Janaina Brusco from University of British Columbia, Can. Financial support from Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) are acknowledged. Special thanks to Dr. Roy E. Larson of University of São Paulo, FMRP/USP (past advisor). Infrastructure support from Marine Biology Center at University of São Paulo (CEBIMar-USP) and Marine Biological Laboratory, Woods Hole-US. Special thanks to Patricia Horta, PhD, IFSP, that revised this chapter.


In a meta-analysis of 963 papers, the range for TOLAC and VBAC rates was large (28-82 percent and 49-87 percent, respectively). Predictors of women having a TOL were having a prior vaginal delivery and settings of higher-level care, namely tertiary care centers [Guise et al, 2010]. Similar findings have been reported in sub-Saharan [Boulvain et al, 1997]; the percentage of TOL ranged from 37% to 97% across reports, with probability of successful vaginal delivery of 69% (95% CI 63-75%). Maternal mortality among all women with a previous cesarean section was 1.9/1000 (95% CI 0-4.3). Uterine rupture and scar dehiscence occurred in 2.1% (95% CI 1.0-3.2). With our restrictions on VBAC, we recorded fewer vaginal deliveries, but also less uterine rupture / dehiscence, as was found in rural Zimbabwe [Spaans et al, 1997]. In settings where such cautions were not applied, higher morbidity levels were observed [Olagbuji et al., 2010, Adanu & McCarthy, 2007; Olusanya & Solanke, 2009; Sepou et al, 2003; Nwokoro et al 2003; Oboro et al, 2010; Wanyonyi & Karuga, 2010]. A large multicenter propective study in a western country with a uniform and well organised delivery care system emphasized the greater perinatal risk associated with a trial of labor [Landon et al, 2004]. Although these findings can be a subject of debate [Greene, 2004]; they must be considered and women deserve to be well informed of the risks and benefits of TOL and VBAC [Kraemer et al, 2004]. A recent systematic review suggests that VBAC is a reasonable choice for the majority of women and found that adverse outcomes were rare for both elective repeat cesarean delivery and trial of labor [Guise JM et al., 2010a, 2010b]. The need for studies identifying patients at greatest risk is of primary importance in

peripheral level. As a result, only 24% of deliveries were attended by a skilled professional. Similar figures have been reported from Tanzania [Olsen et al., 2005]. Many basic health facilities do not even have a midwife, so, many patients have to come directly to the tertiary hospital or go nowhere at all [Gerein N et al, 2006]. Many strategies have been or are being tested to solve this problem. Unfortunately, there is no one single-bullet solution [Dayrit et al, 2010]. These gaps contribute to the poor performance of the health system [Lawn J E., 2009]. Thus, a holistic approach has to be considered for better strengthening of the health system in order to meet the performance goals of the WHO schematic framework [WHO, 2007]

#### **4.4 Cephalopelvic disproportion**

The expression cephalopelvic disproportion (CPD) came into use prior to the 20th century to describe obstructed labor due to disparity between the dimensions of the fetal head and maternal pelvis that preclude vaginal delivery. This term, however, originated at a time when the main indication for cesarean delivery was overt pelvic contracture due to rickets (Olah & Neilson, 1994). CPD can be due to a contracted pelvis or a disproportionately large fetal head and is thus not limited to primary cesarean delivery only [Carbone B., 2000].

In a systematic review of cesarean delivery for maternal indication, Dumont A. et al [Dumont al, 2001] found that cephalopelvic disproportion was the commonest indication, and 1.4% to 8.5% of all deliveries resulted in cesarean birth for this indication. Similarly, a large population based study in West Africa reported that 1% of all deliveries were complicated by CPD [Ould El Jouda D et al, 2001]. The proportion of all cesarean deliveries due to contracted pelvis (a sub-entity of CPD) has been reported to be between 20% in Senegal [Bouillin et al, 1994] and 37.3% in Bobo Dioulasso, Burkina Faso [Bambara et al, 2007]. Comparable trends have been reported in Senegal with mean rates of 31.3% for CPD ranging from 26% to 34.9% between 1992 and 2001 [Cissé et al, 2004; N'Gom PM et al, 2004], as well as Ethiopia (34% [Fesseha et al, 2011]). Similar high incidence rates of CPD have been reported in non sub-Saharan developing countries [Festin et al, 2009]. Our data pointed out the importance of contracted pelvis in CPD. Cephalopelvic disproportion was a major indication of cesarean delivery in our hospital from 1985 to 2003. A mean rate of 39.6% of women who delivered abdominally had some degree of CPD, ranging from 30.3% to 43.4% between 1985 and 2003. In addition, in our study contracted pelvis constituted the vast majority of all CPD (87%). 63.5% of all contracted pelvis cases were found in patients referred most commonly from poor rural settings. The high incidence rates of uterine rupture (an end stage of obstructed labor) recorded in this group may correlate with severity of pelvis contraction and confirmed the close link between referred patients during labor / delivery and need of cesarean reported elsewhere [Amelink – Verburg et al, 2009].

The cause of high rates of contracted pelvis in rural areas may be due to several factors such as genetics, increasing recognition, or the impact of resource scarcity on the female bony pelvis [Cissé et al, 2004; Kurki, 2011]. Special attention must be devoted to malnutrition in sub-Saharan Africa. Malnutrition prevalence remains unfortunately high; the proportion of the population with low daily caloric intake exceed 30% in many countries, and this trend is mirrored by the prevalence of low weight in children under five years old [USAID / West Africa professional paper series, 2008]. Consequently, prevention of obstructed labor can be achieved only through a multidisciplinary approach aimed in the short term at identifying high-risk cases and in the long term at improving nutrition. Early motherhood should be discouraged, and efforts are needed to improve nutrition during infancy, childhood, early adulthood, and pregnancy. Improving the access to and promoting the use of reproductive and contraceptive services will also help reduce the prevalence of this complication [Konje & Ladipo, 2000].

#### **4.5 Previous cesarean delivery**

188 Cesarean Delivery

peripheral level. As a result, only 24% of deliveries were attended by a skilled professional. Similar figures have been reported from Tanzania [Olsen et al., 2005]. Many basic health facilities do not even have a midwife, so, many patients have to come directly to the tertiary hospital or go nowhere at all [Gerein N et al, 2006]. Many strategies have been or are being tested to solve this problem. Unfortunately, there is no one single-bullet solution [Dayrit et al, 2010]. These gaps contribute to the poor performance of the health system [Lawn J E., 2009]. Thus, a holistic approach has to be considered for better strengthening of the health system in order to meet the performance goals of the WHO schematic framework [WHO,

The expression cephalopelvic disproportion (CPD) came into use prior to the 20th century to describe obstructed labor due to disparity between the dimensions of the fetal head and maternal pelvis that preclude vaginal delivery. This term, however, originated at a time when the main indication for cesarean delivery was overt pelvic contracture due to rickets (Olah & Neilson, 1994). CPD can be due to a contracted pelvis or a disproportionately large fetal head and is thus not limited to primary cesarean delivery only [Carbone B., 2000].

In a systematic review of cesarean delivery for maternal indication, Dumont A. et al [Dumont al, 2001] found that cephalopelvic disproportion was the commonest indication, and 1.4% to 8.5% of all deliveries resulted in cesarean birth for this indication. Similarly, a large population based study in West Africa reported that 1% of all deliveries were complicated by CPD [Ould El Jouda D et al, 2001]. The proportion of all cesarean deliveries due to contracted pelvis (a sub-entity of CPD) has been reported to be between 20% in Senegal [Bouillin et al, 1994] and 37.3% in Bobo Dioulasso, Burkina Faso [Bambara et al, 2007]. Comparable trends have been reported in Senegal with mean rates of 31.3% for CPD ranging from 26% to 34.9% between 1992 and 2001 [Cissé et al, 2004; N'Gom PM et al, 2004], as well as Ethiopia (34% [Fesseha et al, 2011]). Similar high incidence rates of CPD have been reported in non sub-Saharan developing countries [Festin et al, 2009]. Our data pointed out the importance of contracted pelvis in CPD. Cephalopelvic disproportion was a major indication of cesarean delivery in our hospital from 1985 to 2003. A mean rate of 39.6% of women who delivered abdominally had some degree of CPD, ranging from 30.3% to 43.4% between 1985 and 2003. In addition, in our study contracted pelvis constituted the vast majority of all CPD (87%). 63.5% of all contracted pelvis cases were found in patients referred most commonly from poor rural settings. The high incidence rates of uterine rupture (an end stage of obstructed labor) recorded in this group may correlate with severity of pelvis contraction and confirmed the close link between referred patients during labor / delivery and need of cesarean reported elsewhere [Amelink – Verburg et al, 2009]. The cause of high rates of contracted pelvis in rural areas may be due to several factors such as genetics, increasing recognition, or the impact of resource scarcity on the female bony pelvis [Cissé et al, 2004; Kurki, 2011]. Special attention must be devoted to malnutrition in sub-Saharan Africa. Malnutrition prevalence remains unfortunately high; the proportion of the population with low daily caloric intake exceed 30% in many countries, and this trend is mirrored by the prevalence of low weight in children under five years old [USAID / West Africa professional paper series, 2008]. Consequently, prevention of obstructed labor can be achieved only through a multidisciplinary approach aimed in the short term at identifying

2007]

**4.4 Cephalopelvic disproportion**

One third of our patients with a history of previous cesarean delivery were allowed a trial of labor (TOL), and the probability of successful vaginal delivery in this group was 50.1%. In our guidelines for trial of labor after cesarean birth (TOLAC), neither labor induction nor labor augmentation were permitted. No TOLAC was attempted when the number of previous cesarean delivery was >1 or in the case of a previous history of uterine rupture. These strict criteria explained our relative low rate of TOLAC.

In a meta-analysis of 963 papers, the range for TOLAC and VBAC rates was large (28-82 percent and 49-87 percent, respectively). Predictors of women having a TOL were having a prior vaginal delivery and settings of higher-level care, namely tertiary care centers [Guise et al, 2010]. Similar findings have been reported in sub-Saharan [Boulvain et al, 1997]; the percentage of TOL ranged from 37% to 97% across reports, with probability of successful vaginal delivery of 69% (95% CI 63-75%). Maternal mortality among all women with a previous cesarean section was 1.9/1000 (95% CI 0-4.3). Uterine rupture and scar dehiscence occurred in 2.1% (95% CI 1.0-3.2). With our restrictions on VBAC, we recorded fewer vaginal deliveries, but also less uterine rupture / dehiscence, as was found in rural Zimbabwe [Spaans et al, 1997]. In settings where such cautions were not applied, higher morbidity levels were observed [Olagbuji et al., 2010, Adanu & McCarthy, 2007; Olusanya & Solanke, 2009; Sepou et al, 2003; Nwokoro et al 2003; Oboro et al, 2010; Wanyonyi & Karuga, 2010]. A large multicenter propective study in a western country with a uniform and well organised delivery care system emphasized the greater perinatal risk associated with a trial of labor [Landon et al, 2004]. Although these findings can be a subject of debate [Greene, 2004]; they must be considered and women deserve to be well informed of the risks and benefits of TOL and VBAC [Kraemer et al, 2004]. A recent systematic review suggests that VBAC is a reasonable choice for the majority of women and found that adverse outcomes were rare for both elective repeat cesarean delivery and trial of labor [Guise JM et al., 2010a, 2010b]. The need for studies identifying patients at greatest risk is of primary importance in sub-Saharan Africa where high levels of morbidity are often reported.

Overall, in sub-Saharan Africa a selective policy of trial of labor after a previous cesarean delivery has a success rate comparable to that observed in developed countries. Vaginal birth after cesarean appears to be relatively safe and applicable in this context and contributes significantly to the global cesarean delivery rate.

#### **4.6 Low rates of elective delivery**

There are many reports emphasising on the high levels of emergency delivery in sub-Saharan hospitals and health centres [Fesseha et al, 2011; Shah et al, 2009; Wylie & Mirza, 2008; Dumont et al, 2001]. In contrast to wealthier countries, planned delivery remains an underused option in Sub-Saharan Africa [Stavrou E. P. et al, 2011]. For example, during the

Determining Factors of Cesarean Delivery Trends

countries.

0% 5% 10% 15% 20% 25% 30% 35% 40% 45%

2010b).

Eyoko.

**7. References**

**6. Acknowledgments**

in Developing Countries: Lessons from Point G National Hospital (Bamako – Mali) 191

widespread access to facilities capable of performing caesarean sections as well as earlier referrals of high risk pregnancies from primary health centers before the onset of complications would likely lead to substantial improvements in maternal and neonatal outcomes. A holistic need assessment will govern improved healthcare delivery strategies and aid progress towards meeting the millennium development goals in developing

Observed cesarean delivery rates

Cesarean delivery rates adjusted for age and parity Cesarean delivery rates adjusted for all maternal characteristics Cesarean delivery rates further adjusted for maternal medical conditions Cesarean delivery rates further adjusted for labor induction Cesarean delivery rates further adjusted for referral status

2003 2004 2005 2006 2007 2008 2009

Fig. 9. Observed rates of cesarean delivery and adjusted rates after sequentially adjusting for age, parity, maternal conditions, obstetric practice and referral status (Teguete I. et al,

To all the medical students who participated in the Point G obstetric database completion: Seydou Traore, Sekou Coulibaly, Marie Lea Dakouo, Aïssata Nene Bah, Seydou Fané, Amadou Fomba, Adama Diarra, Nouhoum Camara, Yakouni dite Hawa Dougnon, Sandrine

Adanu R.M.K. & McCarthy M.Y. (2007); Vaginal birth after cesarean delivery in the West

Althabe F, Belizán J, Villar J, Alexander S, Bergel E, Ramos S, Romero M, Donner A,

African setting. *International Journal of Gynecology and Obstetrics* Vol .98, No 3,

Lindmark G, Langer A, Farnot U, Cecatti JG, Carroli G. & Kestler E. (2004). Latin American Cesarean Section Study Group: Mandatory second opinion to reduce

To Evan and Lauren Oreinstein, for their valuable contribution to this work.

(September 2007), pp. (227–231). PMID: 17603060.

two decades at Point G teaching hospital, only 212 pregnant women underwent labor induction. In many sub-Saharan African countries, labor induction is not common as necessary medications are not readily available. Before the year 2000, oxytocine was the only medication available in Mali for labor induction and was only used for very favorable cases with a Bishop cervical score ≥ 7. Despite the lower rates of labor induction, we observe a mean rate of post-induction cesarean delivery of approximately 90% (Robson group 2). High levels of cesarean delivery following labor induction in nulliparas have been qualified as universal [Brennan et al, 2009 ; Main et al., 2006; McCarthy et al, 2007; Robson, 2001; Costa et al 2010; Yeast et al, 1999]

Unpublished data from the WHO Global Survey on Maternal and Perinatal Health, which included 373 health-care facilities in 24 countries and nearly 300 000 deliveries, showed that 9.6% of the deliveries involved labor induction. Overall, the survey found that facilities in African countries tended to have lower rates of induction of labor (lowest: Niger, 1.4%) compared with Asian and Latin American countries (highest: Sri Lanka, 35.5%) [WHO, 2010].

One point is that many indications of labor induction are associated with preterm delivery. The lack of neonatal resuscitation facilities [Hofmeyr et al, 2009] and the poor outcomes of preterm neonates lead many sub-saharan obstetric teams to avoid preterm labor induction or preterm elective cesarean delivery. Even in hospitals, staffs are frequently not trained in resuscitation and equipment is not available. A national service provision assessments in 6 African countries demonstrated that only 2%–12% of personnel conducting births had been trained in neonatal resuscitation and only 8%–22% of facilities had equipment for newborn respiratory support [Wall et al, 2009]. This important gap certainly impacts clinical decision making in Sub-Saharan obstetric units.

Therefore, it is a challenge for healthcare workers and policymakers dealing with pregnancy management in developing countries to examine critically ways to increase percentage of planned delivery. This challenge can be met firstly with preventive measures at a public health level (e.g. counselling and education), at the pregnant women's level (e.g. improved utilisation of the antenatal care services), and at the caregiver's level (e.g. better selection of cases in order improve the percentage of pregnant referred without emergency, an overt contracted pelvis mustn't begin labor at the level of primary care where obstetric surgery is not available).

#### **5. Conclusion**

From 1985 to 2003, cesarean delivery rates at Point G National Hospital increased substantially. Most of the increase in cesarean delivery rates is explained by higher proportions of outside referrals, cephalopelvic disproportion, and history of previous cesarean delivery. The increased cesarean delivery rate cannot, however, be fully explained by these factors or other characteristics collected by this study, and is likely the multifactorial impact of psychosocial determinants of healthcare utilization and systemic problems of healthcare delivery. These variables are beyond the scope of this study. Future ecological studies addressing clinical, financial, and geographical considerations as well as cultural acceptability of cesarean delivery are needed. Since emergency referrals for caesarean during delivery significantly worsen the maternal and fetal prognosis, more widespread access to facilities capable of performing caesarean sections as well as earlier referrals of high risk pregnancies from primary health centers before the onset of complications would likely lead to substantial improvements in maternal and neonatal outcomes. A holistic need assessment will govern improved healthcare delivery strategies and aid progress towards meeting the millennium development goals in developing countries.

Fig. 9. Observed rates of cesarean delivery and adjusted rates after sequentially adjusting for age, parity, maternal conditions, obstetric practice and referral status (Teguete I. et al, 2010b).

#### **6. Acknowledgments**

190 Cesarean Delivery

two decades at Point G teaching hospital, only 212 pregnant women underwent labor induction. In many sub-Saharan African countries, labor induction is not common as necessary medications are not readily available. Before the year 2000, oxytocine was the only medication available in Mali for labor induction and was only used for very favorable cases with a Bishop cervical score ≥ 7. Despite the lower rates of labor induction, we observe a mean rate of post-induction cesarean delivery of approximately 90% (Robson group 2). High levels of cesarean delivery following labor induction in nulliparas have been qualified as universal [Brennan et al, 2009 ; Main et al., 2006; McCarthy et al, 2007; Robson, 2001; Costa et

Unpublished data from the WHO Global Survey on Maternal and Perinatal Health, which included 373 health-care facilities in 24 countries and nearly 300 000 deliveries, showed that 9.6% of the deliveries involved labor induction. Overall, the survey found that facilities in African countries tended to have lower rates of induction of labor (lowest: Niger, 1.4%) compared with Asian and Latin American countries (highest: Sri Lanka, 35.5%) [WHO,

One point is that many indications of labor induction are associated with preterm delivery. The lack of neonatal resuscitation facilities [Hofmeyr et al, 2009] and the poor outcomes of preterm neonates lead many sub-saharan obstetric teams to avoid preterm labor induction or preterm elective cesarean delivery. Even in hospitals, staffs are frequently not trained in resuscitation and equipment is not available. A national service provision assessments in 6 African countries demonstrated that only 2%–12% of personnel conducting births had been trained in neonatal resuscitation and only 8%–22% of facilities had equipment for newborn respiratory support [Wall et al, 2009]. This important gap certainly impacts clinical decision

Therefore, it is a challenge for healthcare workers and policymakers dealing with pregnancy management in developing countries to examine critically ways to increase percentage of planned delivery. This challenge can be met firstly with preventive measures at a public health level (e.g. counselling and education), at the pregnant women's level (e.g. improved utilisation of the antenatal care services), and at the caregiver's level (e.g. better selection of cases in order improve the percentage of pregnant referred without emergency, an overt contracted pelvis mustn't begin labor at the level of primary care where obstetric surgery is

From 1985 to 2003, cesarean delivery rates at Point G National Hospital increased substantially. Most of the increase in cesarean delivery rates is explained by higher proportions of outside referrals, cephalopelvic disproportion, and history of previous cesarean delivery. The increased cesarean delivery rate cannot, however, be fully explained by these factors or other characteristics collected by this study, and is likely the multifactorial impact of psychosocial determinants of healthcare utilization and systemic problems of healthcare delivery. These variables are beyond the scope of this study. Future ecological studies addressing clinical, financial, and geographical considerations as well as cultural acceptability of cesarean delivery are needed. Since emergency referrals for caesarean during delivery significantly worsen the maternal and fetal prognosis, more

al 2010; Yeast et al, 1999]

making in Sub-Saharan obstetric units.

2010].

not available).

**5.

To all the medical students who participated in the Point G obstetric database completion: Seydou Traore, Sekou Coulibaly, Marie Lea Dakouo, Aïssata Nene Bah, Seydou Fané, Amadou Fomba, Adama Diarra, Nouhoum Camara, Yakouni dite Hawa Dougnon, Sandrine Eyoko.

#### **7. References**

Determining Factors of Cesarean Delivery Trends

(308.e1-8), PMID:19733283.

Organization: Geneva 2010.

(Malawi) 25 –28 mars 2010.

PMID : 20461216.

PMID : 11918936.

doi:10.1186/1742-4755-7-13 PMID: 20579388.

12531845.

73).

in Developing Countries: Lessons from Point G National Hospital (Bamako – Mali) 193

Buekens P., Curtis S. & Alayón S. (2003) Demographic and Health Surveys: cesarean section

Carbone B. (2000). Recommandations pour la pratique clinique. Indications de césarienne en

Chaillet N, Dumont A. (2007). Evidence-Based Strategies for Reducing Cesarean Rates: A Meta Analysis. *Birth* Vol 34, No 1, (March 2007), pp. (53-64), PMID: 17324180. Chou D. et al. (2010). Trends in Maternal Mortality: 1990 to 2008. World Health

Choudhury A.P., Dawson A.J. (2009). Trends in indications for cesarean sections over 7

Cissé C.T., Faye E.O., de Bernis L., Dujardin B., Diadhiou F. (1998). Césariennes au Sénégal :

Cissé CT, Ngom PM, Guissé A, Faye EO, Moreau JC. (2004). Thinking about the evolution of

Commission de l'Union Africaine. Réunion du Comité des experts de la troisième réunion

Costa M. L., Cecatti J. G., Souza J. P., Milanez H. M. & Gülmezoglu A. M. (2010) Using a

Cunningham FG, Gant NF, Leveno KJ, Gilstrap III LC, Hauth JC & Wenstrom KD. (2001). Williams Obstetrics. (21st Edition). McGraw-Hill, New York, 1668 p. Dayrit MM, Dolea C. & Braichet JM. (2010). One piece of the puzzle to solve the human

De Brouwere V. (1997). Appui à la mise en ouvre et à l'évaluation du système de référence avec la périnatalité comme porte d'entrée dans le Cercle. *UNICEF Mali*, 1997. De Brouwere V, Dubourg D, Richard F. & Van Lerberghe W. (2002). Need for cesarean

Dumont A., de Bernis L., Bouvier-Colle M-H & Bréart G, for the MOMA study group (2001).

*midwife,* Vol. 63, No 92, (Winter 2009), pp. (18-19), PMID: 20092138.

29, No 8, (November 2009), pp. (714-717), PMID: 19821664.

(September – October 1998), pp. (369-377) PMID : 98504015.

in spontaneous labor. *Am J Obstet Gynecol* Vol. 201, No 3, (September 2009), pp.

rates in sub-Saharan Africa. *BMJ* Vol 326, No 7381, (January 2003), p. 136, PMID:

cas de dystocie.*J Gynecol Obstet Biol Reprod*; Vol 29, No Suppl. n° 2, (2000), pp. (68 –

years in a Welsh district general hospital. *Journal of Obstetrics and Gynaecology,* Vol

couverture des besoins et qualité des services. *Cahiers Santé* Vol. 8, No 5,

cesarean section rate at University Teaching Hospital of Dakar between 1992 and 2001. *Gynecol Obstet Fertil.* Vol 32, No 3, (March 2004) pp. (210-217), 15123118. Cohain J.S. (2009). Documented causes of unneCesareans. *Midwifery today with international*

conjointe en 2010 de la Conférence des ministres de l'économie et des finances de l'Union africaine et de la Conférence des ministres africains des finances, de la planification et du développement économique de la Commission économique pour l'Afrique. Rapport 2010 sur l'évaluation des progrès accomplis par l'Afrique vers la réalisation des Objectifs du Millénaire pour le développement. Lilongwe

Cesarean Section Classification System based on characteristics of the population as a way of monitoring obstetric practice. *Reproductive Health* Vol 7, No 13, (June 2010),

resources for health crisis. *Bull World Health Organ.* Vol. 88, No 5, (May 2010), p: 322

sections in west Africa. *The Lancet* Vol 359, No 9310 (March 2002) pp : 974 – 975,

Cesarean section rate for maternal indication in sub-Saharan Africa: a systematic

rates of unnecessary cesarean sections in Latin America: a cluster randomised controlled trial. *Lancet*, Vol 363, No 9425, (June 2004), pp. (1934-1940). PMID: 15194252.

Althabe F, Sosa C, Belizán JM, Gibbons L. & Jacquerioz F. (2006). Cesarean section rates and

Amelink-Verburg MP, Rijnders ME, Buitendijk SE. A trend analysis in referrals during

Andriamady Rasoarimahandry CL, Andrianarivony MO & Ranjalahy RJ. (2001). Indications

Ba K. S. (2011). Evaluation Finale de l'Initiative Vision 2010. Réunion d'Evaluation Finale de

Ba'aqeel H.S. (2009). Cesarean delivery rates in Saudi Arabia: A tenyear review. *Annals of Saudi Medicine* Vol. 29, No 3, (May - June 2009), pp. (179-183). PMID : 19448379. Bambara M, Fongan E, Dao B, Ouattara H, Lankoande J. & Kone B. (2007). La césarienne en

(Burkina Faso). *Méd Afrique Noire*, Vol. 54 No 6, (2007), pp. (343-348). Barros FC, Vaughan JP, Victora CG & Huttly SRA. (1991). Epidemic of Cesarean sections in Brazil. *Lancet,* Vol 338, No 8760, (July 1991), pp. (167-169). PMID: 1677075. Béla G., Péter N. & János T. (2009). Trends in prevalence of cesarean section in Uzsoki

factors. *Magyar Noorvosok Lapja* Vol. 72 No 6, (2009), pp. (269-272).

(November 1999) pp. (1397–402). PMID: 10574855.

*studies* Calverton, MD: ORC Macro, No. 7, (2003), p. 62.

Vol. 70, No 10, (May 2010) pp. (1544–1549), PMID: 20219278.

(November – December 1994), pp. (399-406), PMID : 7850191.

104, No 12 (December 1997), pp. (1385-1390), PMID: 9422017.

Belizán J. M., Althabe F., Barros F. C. & Alexander S. (1999). Rates and implications of

Bell J, Curtis SL & Alayón S. (2003). Trends in delivery care in six countries*. DHS analytical*

Betran AP, Merialdi M, Lauer JA, Bing-Shun W, Thomas J, Van Look P & Wagner M. (2007)

*Perinatal Epidemiol* Vol. 21 No 2, (March 2007), pp. (98-113), PMID: 17302638. Bogg L., Huang K., Long Q., Shen Y. & Hemminki E. (2010). Dramatic increase of Cesarean

Bouillin D, Fournier G, Gueye A, Diadhiou F & Cissé CT. (1994) Epidemiological

Boulvain M, Fraser WD, Brisson-Carroll G, Faron G & Wollast E. (1997). Trial of labor after

Brennan DJ, Robson MS, Murphy M, et al. (2009). Comparative analysis of international

15194252.

17150064.

(June 2009), pp. (923-32). PMID: 19522796

la VISION 2010 BAMAKO 1 - 6 Octobre 2011

rates of unnecessary cesarean sections in Latin America: a cluster randomised controlled trial. *Lancet*, Vol 363, No 9425, (June 2004), pp. (1934-1940). PMID:

maternal and neonatal mortality in low-, medium-, and high-income countries: an ecological study. *Birth*, Vol. 33, No 4, (December 2006), pp. (270-277). PMID:

pregnancy and labor in Dutch midwifery care 1988-2004. *BJOG,* Vol 116, No 7,

and prognosis of cesarean section at Befelatanana maternity unit--Central University Hospital of Antananarivo (apropos of 529 cases, during the year 1998). *Gynecol Obstet Fertil*. Vol. 29, No 12, (December 2001), pp. (900-4). PMID : 11802553.

milieu africain: à propos de 440 cas à la maternité du CHUSS de Bobo-Dioulasso

Hospital between 1st January, 1999 and 30th june, 2009. Analysis of some suspected

cesarean sections in Latin America: ecological study. *BMJ* 1999; Vol. 319, No 7222,

Rates of cesarean section: analysis of global, regional and national estimates. *Paediat*

deliveries in the midst of health reforms in rural China. *Social Science & Medicine,*

surveillance and obstetrical dystocias surgery in Senegal. *Sante*, Vol. 4, No 6,

cesarean section in sub-Saharan Africa: a meta-analysis. *Br J Obstet Gynaecol.* Vol

cesarean delivery rates using 10-group classification identifies significant variation

in spontaneous labor. *Am J Obstet Gynecol* Vol. 201, No 3, (September 2009), pp. (308.e1-8), PMID:19733283.

Determining Factors of Cesarean Delivery Trends

(47-54). PMID: 17385382.

Sons, New York.

pp. (11 – 18).

Knippenberg R.,

(137-153). PMID: 17132029.

1997), pp. (S209-18). PMID: 9389633.

April 2009), pp. (458-469). PMID : 19554995.

*Noire* Vol. 53, No 5, (2006), pp. (293-298).

(65.e1-65.e6). PMID: 19819416.

(September 2004), pp. (273-281). PMID: 15276307.

1992), pp. (606-8). PMID: 1334988

in Developing Countries: Lessons from Point G National Hospital (Bamako – Mali) 195

Holtz SA & Stanton CK. (2007). Assessing the quality of cesarean birth data in the

Horan TC, Gaynes RP, Martone WJ, Jarvis WR, Emori TG. (1992) CDC definitions of

Hosmer DW Jr, Lemeshow S. (1989). *Applied logistic regression*. pp. (131–3), John Wiley &

Howell S., Johnston T., MacLeod S.-L. (2009) Trends and determinants of cesarean sections

*Gynaecology* Vol. 49, No 6, (December 2009), pp. (606-611). PMID: 20070708. Ijaiya M.A. and Aboyeji P.A. (2001). Cesarean delivery: the trend over a ten-year period at

Ikeako LC, Nwajiaku L, Ezegwui HU. (2009). Cesarean section in a secondary health hospital in Awka, Nigeria. *Niger Med J* Vol. 50, No…, (2009), pp. (64-67). Jain N.J., Kruse L.K., Demissie K., Khandelwal M. (2009). Impact of mode of delivery on

*Neonatal Medicine* Vol. 22, No 6, (June 2009), pp. (491-500). PMID: 19504405. James C D., Hanson K, McPake B., Balabanova D., Gwatkin D., Hopwood I. Kirunga C.,

Meessen B., Morris S.l S., Preker A, Souteyrand Y., Tibouti A., Villeneuve P.l & Xu K. (2006).

Kandeh HB, Leigh B, Kanu MS et al. (1997). Community motivators promote use of

Karlström A., Ra°destad I., Eriksson C., Rubertsson C., Nystedt A., and Hildingsson I.

Khawaja M, Kabakian-Khasholian T, Jurdi R. (2004). Determinants of cesarean section in

Kizonde K, Kinekinda X, Kimbala J, Kamwenyi K. (2006). La césarienne en milieu africain;

Klemetti, R., Che, X., Gao, Y., Raven, J., Wu, Z., Tang, S., Hemminki, E. (2010). Cesarean

Study. *Birth* Vol. 37, No 1, (March 2010), pp (11 – 20). PMID: 20402717. Khawaja, M., Choueiry, N., Jurdi, R. (2009). Hospital-based cesarean section in the Arab

Demographic and Health Surveys. *Stud Fam Plann*. Vol 38, No 1, (March 2007); pp.

nosocomial surgical site infections, 1992: a modification of CDC definitions of surgical wound infections. *Infect Control Hosp Epidemiol* Vol. 13, N°10: (October

births in Queensland, 1997-2006. *Australian and New Zealand Journal of Obstetrics and*

Ilorin, Nigeria. *The Nigerian Journal of Surgical Research*, Vol. 3, No 1 (March 2001),

neonatal complications: Trends between 1997 and 2005. *Journal of Maternal-Fetal and*

To Retain or Remove User Fees? Reflections on the Current Debate in Low- and Middle-Income Countries. *Appl Health Econ Health Policy* Vol. 5, No 3, (2006), pp.

emergency obstetric services in rural Sierra Leone. The Freetown/Makeni PMM Team. *International Journal of Gynaecology and Obstetrics* Vol. 59, Suppl 2, (November

(2010). Cesarean Section without Medical Reason, 1997 to 2006: A Swedish Register

region: An overview. *Eastern Mediterranean Health Journal*, Vol. 15, No 2, (March –

Egypt: evidence from the demographic and health survey. *Health Pol* Vol. 69, No 3,

exemple de la maternité centrale Sendwe de Lubumbashi, R. D. Congo. *Méd Afrique*

section delivery among primiparous women in rural China: an emerging epidemic. *American Journal of Obstetrics and Gynecology* Vol. 202, No 1, (January 2010), pp.

review. *The Lancet*, Vol. 358, No 9290, (October 2001), pp. (1328–334), PMID: 11684214.

El-Khoury M, Gandaho T, Arur A, Keita B, & Nichols L. (2011). Improving Access to Life-

Health Services: The Effects of Removing User Fees for Cesareans in Mali. Bethesda, MD:

Faundes A, Cecatti JG. (1993). Which policy for Cesarean section in Brazil? An analysis of

Fesseha N., Getachew A., Hiluf M., Gebrehiwot Y., Bailey P. (2011). A national review of

Festin MR, Laopaiboon M, Pattanittum P, Ewens MR, Henderson-Smart DJ, Crowther CA;

Geidam A.D., Audu B.M., Kawuwa B.M. & Obed J.Y.(2009) Rising trend and indications of

Graham W. (1998). The scandal of the century. *Br J Obstet Gynaecol* Vol. 105, No 4, (April

Greene M. (2004). Vaginal Birth After Cesarean Delivery Revisited. *New England Journal of Medicine* Vol. 351, No 25, (December 2004), pp. (2647-2649). PMID: 15598961. Guihard P, Blondel B (2001).Trends in risk factors for cesarean sections in France between

Guise JM, Eden K, Emeis C, Denman MA, Marshall N, Fu RR, Janik R, Nygren P, Walker M,

Hofmeyr GJ, Haws RA., Bergström S, Lee ACC, Okong P, Darmstadt GL., Mullany LC.,

*Assess (Full Rep)*. No. 191, (March 2010), pp. (1-397). PMID : 20629481. Guise JM, Denman MA, Emeis C, Marshall N, Walker M, Fu R, Janik R, Nygren P, Eden KB,

*Pregnancy Childbirth.* Vol. 9, No 9, (May 2009) p:17, PMID: 19426513. Fournier P, Dumont A, Tourigny C, Dunkley G & Draméc S. (2009). Improved access to

*Health Systems 20/20*, April 2011, Abt Associates Inc.

115, No 1, (October 2011) pp. (106–111), PMID: 21872239.

11684214.

saving Maternal

(30–8), PMID: 19197402.

20502300.

19815204.

(May 2006) pp. (40-50). PMID: 16713878.

(January 2001), pp. (48-55). PMID: 11213004.

1998), pp. (375-376). PMID: 9609258.

review. *The Lancet*, Vol. 358, No 9290, (October 2001), pp. (1328–334), PMID:

trends and consequences. *Health Policy Plann* Vol. 8 No 1, (March 1993), pp. (33-42).

cesarean delivery in Ethiopia. *International Journal of Gynecology and Obstetrics* Vol.

SEA-ORCHID Study Group. (2009) Cesarean section in four South East Asian countries: reasons for, rates, associated care practices and health outcomes. *BMC*

comprehensive emergency obstetric care and its effect on institutional maternal mortality in rural Mali. *Bull World Health Organ* Vol. 87, No 1, (January 2009), pp.

cesarean section at the university of Maiduguri teaching hospital, Nigeria. *Annals of African Medicine*, Vol. 8, No 2, (April – June 2009) pp. (127-132). PMID: 19805945. Gerein N, Green A, Pearson S. (2006). The implications of shortages of health professionals

for maternal health in sub-Saharan Africa. *Reprod Health Matters* Vol. 14, No 27,

1981 and 1995: lessons for reducing the rates in the future. *BJOG*. Vol. 108, No 1,

McDonagh M. (2010a). Vaginal birth after cesarean: new insights. *Evid Rep Technol*

McDonagh M. (2010b). Vaginal birth after cesarean: new insights on maternal and neonatal outcomes. *Obstet Gynecol.* Vol. 115, No 6, (June 2010), pp. (1267-78). PMID:

Shwe Oo EK, & Lawn JE. (2009). Obstetric care in low-resource settings: What, who, and how to overcome challenges to scale up? *International Journal of Gynecology and Obstetrics* Vol. 107, Suppl 1, (October 2009), pp. (S21–S45). PMID:

Determining Factors of Cesarean Delivery Trends

17627688.

258).

20804350.

8553342.

PMID: 17011392.

(July 2009), p 30. PMID: 19622146.

pp. (116-20). PMID: 15786620.

pp. (S219-24). PMID: 9389634.

in Developing Countries: Lessons from Point G National Hospital (Bamako – Mali) 197

Mbaye EM, Dumont A, Ridde V, Briand V. (2011). Doing more to earn more: cesarean

Menacker F, Declercq E, Macdorman MF. (2006). Cesarean delivery: background, trends,

Muganyizi P. S and Kidanto H. L. (2009). Impact of change in maternal age composition on

Naidoo N., Moodley J. (2009). Rising rates of Cesarean sections: an audit of Cesarean

Ngom PM, Cisse CT, Cisse ML, Faye EO, Moreau JC. (2004). Epidemiology and prognosis of

Nwakoby B, Akpala C, Nwagbo D et al. (1997). Community contact persons promote

Nwokoro C. A., Njokanma O. F., Orebamjo T., and Okeke G. C. E. (2003). Vaginal birth after

Oboro V., Adewunmi A., Ande A, Olagbuji B., Ezeanochie M. & Oyeniran A. (2010).

Olagbuji B., Ezeanochie M.& Okonofua F. (2010). Predictors of successful vaginal delivery

Olsen OE, Ndeki S, Norheim OF. (2005). Human resources for emergency obstetric care in

Olusanya B O., Solanke O A. (2009). Adverse neonatal outcomes associated with trial of

Onsrud L, Onsrud M. (1996). Increasing use of cesarean section, even in developing

*Gynaecol* Vol. 101, No 1, (January 1994), pp. (1 – 3). PMID: 8297861.

health.com/content/3/1/5] PMID: 16053519.

pp. (135–139). PMID: 19647823.

Vol. 23, No. 4, (July 2003) pp. (392–393). PMID: 12881079.

*Publique*. Vol. 23, No 3, (May-June 2011), pp. (207-19). PMID: 21896215. McCarthy FP, Rigg L, Cady L, Cullinane F. (2007). A new way of looking at Cesarean section

sections based on three cases of exemption from payment in Senegal. *Sante*

births. *Aust N Z J Obstet Gynaecol* Vol 47, No 4, (August 2007), pp. (316-20). PMID:

and epidemiology. *Semin Perinatol.* Vol. 30, No 5, (October 2006), pp. (235-41).

the incidence of Cesarean section and low birth weight: analysis of delivery records at a tertiary hospital in Tanzania, 1999–2005. *BMC Pregnancy and Childbirth,* Vol. 9,

sections in a specialist private practice. *SA Fam Pract* Vol. 51, No 3, (2009), pp. (254-

cesarean sections in University Hospital of Dakar. *Dakar Med.* Vol. 49, No 2, (2004),

utilization of obstetric services, Anambra State, Nigeria. The Enugu PMM Team. *International Journal of Gynaecology and Obstetrics* Vol. 59, Suppl. 2, (November 1997),

primary cesarean section: the fetal size factor. *Journal of Obstetrics and Gynaecology,*

Morbidity associated with failed vaginal birth after cesarean section. *Acta Obstetricia et Gynecologica.* Vol. 89, No 9, (September 2010), pp. (1229–1232). PMID:

after previous cesarean section in a Nigerian tertiary hospital. *Journal of Obstetrics and Gynaecology*, Vol 30, No 6, (August 2010), pp. (582–585). PMID: 20701507. Olah KSJ, Neilson J. (1994). Failure to progress in the management of labor. *Br J Obstet*

northern Tanzania: distribution of quantity or quality? *Hum Resources Health* Vol. 3, No 5, (July 2005): 12 p. [Available from: www.human-resources-

labor after previous cesarean delivery in an inner-city hospital in Lagos, Nigeria. *International Journal of Gynecology and Obstetrics* Vol. 107, No 2, (November 2009),

countries. *Tidsskr Nor Laegeforen* Vol. 116, No 1, (January 1996), pp. (67-71). PMID:

Konje J C and Ladipo O A. Nutrition and obstructed labor (2000). *Am J Clin Nutr* Vol 72,

Kowalewski A., Jahn A., Kimatta S.S. (2000). Why Do At-Risk Mothers Fail To Reach

Kraemer D. F., Berlin M., and Guise J-M. The relationship of health care delivery system

Künzel W., Herrero J., Onwuhafua P., Staub T., Hornung C. (1996) Maternal and perinatal

Kwawukume E. Y. (2001). Cesarean section in developing countries. *Best Practice & Research*

Landon MB, Hauth JC, Leveno KJ, Spong CY, Leindecker S, Varner MW, et al. (2004).

Leone T., Padmadas S S., Matthews Z. (2008). Community factors affecting rising cesarean

*Medicine*, Vol 67, No 8, (October 2008) pp. (1236–1246). PMID: 18657345. Mariko M. (2003). Quality of care and the demand for health services in Bamako, Mali: the

*Medicine* Vol. 56, No 6, (March 2003), pp. (1183–1196). PMID: 12600357. Lawn J E., Kinney M, Lee A CC, Chopra M, Donnay F, Paul V. K., Bhutta Z A., Bateman M,

Lawn J. E., Lee A. CC, Kinney M., Sibley L., Carlo W. A., Paul V. K., Pattinson R., Darmstadt

*Obstetrics*, Vol. 107, Suppl. 1, (October 2009) ; pp. (S5–S19). PMID : 19815202. Maiga Z, Traoré Nafo F & El Abassi A (1999) La réforme du secteur santé au Mali (1989- 1996). *Studies in Health Services Organisation & Policy* 12. ITGPress, Antwerpen. Main EK, Moore D, Farrell B, et al. (2006). Is there a useful cesarean birth measure?

Malvasi A., Tinelli A., Guido M., Zizza A., Cotrino G., Vergari U. (2009). The increasing

Suppl. 1, (October 2009), pp. (S123–S142). PMID: 18815205.

(1644-51), discussion (1651-2). PMID: 16643812.

Vol. 5, No 3, (2009), pp. (176-183)

*Reproductive Biology,* Vol. 69, No 1, (1996) pp. (11-17). PMID: 8909951. Kurki H.K. (2011). Compromised skeletal growth? Small body size and clinical contraction

Referral Level? Barriers Beyond Distance and Cost. *Afr J Reprod Health,* Vol. 4, No 1,

characteristics and legal factors to mode of delivery in women with prior cesarean section: a systematic review. *Women's Health Issues* Vol. 14, No 3, (May – June 2004),

health in Mali, Togo and Nigeria. *European Journal of Obstetrics & Gynecology and*

thresholds for the female pelvic canal. *Int. J. Paleopathol.* (2011),

*Clinical Obstetrics & Gynaecology*, Vol. 15, No. 1, (February 2001), pp. 165 – 178.

Maternal and perinatal outcomes associated with a trial of labor after prior cesarean delivery. *N Engl J Med*. Vol. 351, No 25, (December 2004), pp. (2581-9).

section rates in developing countries: An analysis of six countries. *Social Science &*

specific roles of structural, process, and outcome components. *Social Science &*

Darmstadt G L. (2009). Reducing intrapartum-related deaths and disability: Can the health system deliver? *International Journal of Gynecology and Obstetrics* Vol. 107,

G. L. (2009). Two million intrapartum-related stillbirths and neonatal deaths: Where, why, and what can be done? *International Journal of Gynecology and*

Assessment of the nulliparous term singleton vertex cesarean birth rate as a tool for obstetric quality improvement. *Am J Obstet Gynecol* Vol 194, No 6, (June 2006), pp.

trend in cesarean sections in south eastern italy: Medical and biopolitical analysis of causes and possible mechanisms for its reduction. *Current Women's Health Reviews*

Suppl 1, (July 2000); pp. (291S–7S). PMID: 19871595.

(2000), pp. (100-109).

pp. (94–103). PMID: 15193637.

doi:10.1016/j.ijpp.2011.10.004

PMID: 11359321.

PMID: 15598960.

Determining Factors of Cesarean Delivery Trends

21251270.

16753484.

pp. (S47–S64). PMID: 19815203.

in Developing Countries: Lessons from Point G National Hospital (Bamako – Mali) 199

Stanton C.K., Dubourg D., De Brouwere, V., Pujades, M. & Ronsmans C. (2005). Reliability

Stein W., Katundo I., Byengonzi B. (2008). Cesarean Rate and Uterine Rupture: A 15-year

Teguete I., Mounkoro N., Traore Y., Dolo T., Kayenta K., Diallo A., Sissoko A., Djire M.,

Teguete I., Mounkoro N., Traore Y., Dolo T., Kayentao K., Sissoko A., Traore M., Dolo A.

Teguete I., Traore Y., Dennis N., Mounkoro N., Traore M. and Dolo A. (2010). A 19-year

Teguete I, Mounkoro N, Traoré Y, Dolo T, Sissoko A, Djire MY Traoré M, Dolo A.

Libreville (Gabon), November 22nd – 26th, 2010b. Abstract book, page 20. UN. (1995). Report of the International Conference on Population and Development, (ICPD),

van Dillen J, Meguid T, Petrova V & van Roosmalen J.(2007) Cesarean section in a semi-rural

Wall S. N., Lee A. CC., Niermeyer S., English M., Keenan W. J., Carlo W., Bhutta Z. A., Bang

*Neonatol* Vol. 212, No 6, (2008), pp. (222-225). PMID: 19085739.

*Obstetrics*, Vol. 107, Suppl. 2, (October 2009), Page S357.

on Population and Development. *UN*, New York, 1995.

(March 2010), pp. (194 – 198). PMID: 19944419.

*Organization* Vol 83, Vol 6, (June 2005), pp. (449-455). PMID: 15976896. Stanton C., Ronsmans C., and the Baltimore Group on Cesarean. (2008). Recommendations

of data on cesarean sections in developing countries. *Bulletin of the World Health*

for Routine Reporting on Indications for Cesarean Delivery in Developing Countries. *Birth* Vol. 35, No 3, (September 2008), pp. (204 – 2011). PMID: 18844646. Stavrou E. P., Ford J. B., Shand A. W., Morris J. M., Roberts C. L. (2011). Epidemiology and

trends for Cesarean section births in New South Wales, Australia: A populationbased study. *BMC Pregnancy and Childbirth* Vol. 11, No 8, (January 2011). PMID:

Hospital-Based Observational Retrospective Study in Rural Tanzania. *Z Geburtshilfe*

Traore M., Dolo A. Malaria and pregnancy at Gabriel Toure Teaching Hospital in Bamako between 2003 and 2007. *Journal de la SAGO*, Vol. 9, No 1, (2008), pp. (12-16).

(2009). O928 Malaria and pregnancy at the Gabriel Toure teaching hospital in Bamako (Mali) between 2003 and 2007. *International Journal of Gynecology &*

retrospective investigation of maternal mortality at Point G National Hospital, Bamako, Mali. International Journal of Gynaecology and Obstetrics, Vol: 108, No 3,

Influencing factors of delivery rates at Gabriel Toure Teaching hospital, Bamako, Mali. Proceedings of the XIth African Society of Gynecology and Obstetrics (SAGO).

Cairo, 5-13 September 1994, Programme of Action of the International Conference

hospital in northern Namibia. *BMC Pregnancy Childbirth* Vol 72, No 2, (March 2007), 6 p. [Available from: www.biomedcentral.com/1471-2393/7/2] PMID: 17346332. Villar J, Valladares E, Wojdyla D, Zavaleta N, Carroli G, Velazco A, Shah A, Campodonico

L, Bataglia V, Faundes A, Langer A, Narvaez A, Donner A, Romero M, Reynoso S, de Padua KS, Giordano D, Kublickas M, Acosta A, for the WHO 2005 global survey on maternal and perinatal health research group. (2006). Cesarean delivery rates and pregnancy outcomes: the 2005 WHO global survey on maternal and perinatal health in Latin America. *Lancet* Vol 367, No 9535, (2006), pp. (1819-29). PMID:

A., Narayanan I., Ariawan I. & Lawn J. E. (2009). Neonatal resuscitation in lowresource settings: What, who, and how to overcome challenges to scale up? *International Journal of Gynecology and Obstetrics* Vol. 107, Suppl. 1, (October 2009),

Ould El Jouda D., Bouvier-Colle M.-H., MOMA Group. (2001). Dystocia: a study of its

Riviere M. (1959). Mortalité maternelle au cours de l'état gravido-puerpéral, avortement exceptés. *Bull soc, gynécol Obstét., Congrés de Paris* No 11, (1959), pp. (141-272). Robitail S, Gorde S, Barrau K, Tremouille S, Belec M. (2004). How much does a cesarean

Robson MS. (2001). Classification of Cesarean Sections. *Fetal and Maternal Medicine Review*

Ronsmans C, Damme W V., Filippi V, Pittrof R. (2002). Need for cesarean sections in West Africa. *The Lancet* Vol 359, No 9310, (March 2002), p 974. PMID: 11861198. Ronsmans C., Etard J. F., Walraven G., Høj L., Dumont A., de Bernis L. and Kodio B.

Rosenfield A, Maine D. (1985). Maternal mortality – a neglected tragedy. Where is the M in MCH? *Lancet* Vol. 2, No 8446, (July 1985), pp. (83-85). PMID: 2861534. Rudge MV, Maesta I, Moura PM, Rudge CV, Morceli G, Costa RA, Abbade J, Peracoli JC,

Group C. (2011). The safe motherhood referral system to reduce cesarean sections and

Samaké S, Traoré SM, Ba S, Dembélé É, Diop M, Mariko S, et al. (2007). Demography and

Sepou A, Nguembi E, Yanza M-C, Penguélé A, Ngbalé R., Kouabosso A., Domandé-

Sørbye I K, Vangen S, Oneko O, Sundby J and Bergsjø P. (2011). Cesarean section among

PMID: 21798016. http://www.biomedcentral.com/1471-2393/11/55 Spaans W. A., van der Velde F. H., & van Roosmalen J. (1997). Trial of labor after previous

11502297.

14516306.

*la Santé* (2007).

19782977.

Witkin SS, Calderon IM,

2004), pp. (274-9). PMID: 17304751.

Vol 12, No 1, (January 2001), pp. (23-39).

1, (November 2011), pp. (34). PMID: 22108042.

frequency and risk factors in seven cities of west Africa. *International Journal of Gynecology & Obstetrics* Vol 74, No 2 (August 2001), pp. (171 – 178). PMID:

section cost in Madagascar? Socio-economical aspects and cesarean sections rate in Toamasina, Madagascar 1999-2001. *Bull Soc Pathol Exot.* Vol. 97, No 4, (November

Maternal mortality and access to obstetric services in West Africa. *Tropical Medicine and International Health*. Vol. 8, No 10, (October 2003), pp. (940–948). PMID:

perinatal mortality - a cross-sectional study [1995-2006]. *Reprod Health.* Vol. 23, No

Health SurveyMali 2006. Bamako: *Cellule de Planification et de Statistique, Ministère de*

Modanga Z., Gaunefet C, Nali M. N. (2003) Utérus cicatriciel : suivi de 73 parturientes à la Maternité centrale de Bangui (République centrafricaine). *Cahiers d'études et de recherches francophones / Santé 2003*. Vol. 13, N. 4, (2003), pp. (231-3). Shah A., Fawole B., M'Imunya J. M., Amokrane F., Nafiou I., Wolomby J-J., Mugerwa K.,

Neves I., Nguti R., Kublickas M., Mathai M. Cesarean delivery outcomes from the WHO global survey on maternal and perinatal health in Africa. *International Journal of Gynecology & Obstetrics*, Vol. 107, No 3, (December 2009), pp. (191-197). PMID:

referred and selfreferred birthing women: a cohort study from a tertiary hospital, northeastern Tanzania. *BMC Pregnancy and Childbirth* Vol. 11, No 55, (July 2011),

cesarean section in rural Zimbabwe. *European Journal of Obstetrics & Gynecology and Reproductive Biology* Vol. 72, No 1, (March 1997), pp. (9 – 14). PMID: 9076415.

http://www.who.int/reproductivehealth/topics/best\_practices/global\_survey)

Wanyonyi S. Z. & Karuga R. N. (2010). The utility of clinical care pathways in determining

Wanyonyi S, Sequeira E, & Obura T. (2006). Caesarian section rates and perinatal outcome at

Weil O & Fernandez H. (1999). Is safe motherhood an orphan initiative? *Lancet,* Vol. 354, No

Wenjuan W, Alva S., Wang S., & Fort A. (2011). Levels and Trends in the Use of Maternal

West African regional food for peace office. (2008). Understanding Child Malnutrition in the

WHO (2010). Global Survey on Maternal and Perinatal Health. Induction of labor data.

 http://www.who.int/reproductivehealth/topics/best\_practices/global\_survey) World Health Organization. (2007). Everybody's business: Strengthening health systems to improve health outcomes. WHO's framework for action. *Geneva: WHO*; 2007 Wylie B. J. & Mirza F. G. (2008). Cesarean Delivery in the Developing World. *Clinics in Perinatology*, Vol. 35, No 3, (September 2008), pp. (571-582). PMID: 18952023. Yeast J. D., Jones A., & Poskin M. (1999). Induction of labor and the relationship to cesarean

(December 2006), pp. (651-658). PMID: 17685209.

Calverton, Maryland, USA: ICF Macro.

*Africa professional paper series* N°6 (June 2008).

9182, (September 1999), pp. (940–43). PMID: 10489970.

Geneva, World health Organization, 2010 (available at:

3 Pt 1, (March 1999), pp. (628-33). PMID: 10076139.

(1690–1). PMID: 9832001.

PMID: 20946628.

perinatal outcomes for women with one previous cesarean section; a retrospective service evaluation. *BMC Pregnancy and Childbirth,* Vol. 10, No 62, (October 2010),

the Aga Khan University Hospital, Nairobi. *East Afr Med J* Vol. 83, No 12,

Health Services in Developing Countries. *DHS Comparative Reports* 2011; No. 26.

Sahel: A Case Study from Goundam Cercle, Timbuktu Region, Mali. *USAID / West*

delivery: A review of 7001 consecutive inductions. *Am J Obstet Gynecol,* Vol 180, No

cohort studies of common outcomes. *JAMA* Vol. 280, No 19, (November 1998), pp.

Zhang J. & Yu KF. (1998). What's the relative risk? A method for correcting the odds ratio in

### *Edited by Raed Salim*

This book provides broad, science-based information regarding the most common major surgical procedure performed, i.e. Cesarean Delivery. The book provides relevant scientific literature regarding epidemiology and rates of cesarean delivery in low and high income countries and the impact of the disparities in the rate of cesarean delivery between countries. In addition, the book systematically reviews the relevant scientific literature regarding all perioperative considerations with a broad cover of anesthetic techniques, drugs and difficulties that anesthesiologists may encounter during cesarean delivery. Care of the neonate after cesarean and crucial guidelines for obese women undergoing cesarean are also provided. The book was written by distinguished experts from different disciplines to ensure complete and accurate coverage of the recent scientific and clinical advances and to bring care providers and purchasers up to date including essential information to help improve health care quality.

Cesarean Delivery

Cesarean Delivery

*Edited by Raed Salim*

Photo by megaflopp / iStock


**1. Introduction**

Tungsten heavy alloys (WHA) have been used in many fields, including aerospace, defense, military, nuclear, electronics, and marine industries, due to their high melting point and density, excellent thermal conductivity, low thermal expansion, good corrosion resistance, and superior comprehensive properties at high temperatures [1,2]. They have also been proven to be ideal facing-plasma materials in the nuclear industry [3,4]. The 90W-7Ni-3Fe allow, a typical tungsten heavy alloy, which consists of tungsten (90 wt.%), Nickel (7 wt.%) and Iron (3 wt.%), possesses good mechanical properties due to the addition of Ni and Fe, while retaining high-density. In addition, Ni and Fe play a key role in the suppression of cracks in the fabrication of tungsten because of the nature of the brittleness of tungsten at room temperature [5]. Traditionally, 90W-7Ni-3Fe is processed by solid and liquid sintering. A mixture of tungsten, nickel, and iron powder was prepared and then sintered at a certain temperature, such as 1400 ◦C, for a fixed time in a vacuum or inert gas atmosphere [6,7]. Usually, sintered samples need to be treated by isostatic pressing or other heat treatments to reduce their porosity and avoid hydrogen embrittlement [8–10]. However, it is di fficult, or even impossible, to obtain complex components of a tungsten heavy alloy by conventional processes. Thus, additive manufacturing (AM) may be an alternative manufacturing process for high melting point refractory metals, such as tungsten and its alloys.

Selective laser melting (SLM), as a metal additive manufacturing technology, has been proven to be a promising technology in the high-accuracy and integrated fabrication of metallic components. SLM employs a high-energy laser beam to melt metallic powder layer by layer, according to 2D slice data. SLM is a multidisciplinary cross-technology involving mechanical engineering, material science, optics, software, and has attracted much attention from many fields. Deprez et al. [11] produced a complex high-density tungsten collimator. The produced collimator was geometrically accurate, and the tested values of sensitivity and resolution were close to the expected results of the CAD design. The relative density of the SLM pure tungsten prepared by Zhang et al. [12] reached 82%, who found the formation of nanocrystalline in the tungsten samples fabricated by SLM. Zhou et al. [13] analyzed the balling phenomena in the process of SLM-tungsten and proposed a competitive mechanism of spreading and solidification to explain the balling phenomena. Enneti et al. [14] investigated the e ffects of scan speed and hatch spacing on the relative density of SLM pure tungsten, but the highest relative density was only 75%. The relative density of the SLM tungsten prepared by Wen et al. [15] reached 98.7%, and they studied the e ffects of process parameters on the surface morphology, microstructure, and properties of SLM pure tungsten. Similarly, Tan et al. [16] also obtained SLM tungsten with a relative density of 98.5% and analyzed the e ffects of di fferent laser powers and scan speeds on the SLM's surface morphology, microstructure, and properties. All the previous studies on SLM tungsten indicated that the crack phenomenon was inevitable due to the inherent brittle nature of tungsten [17–19]. Therefore, several measures of crack-suppression for SLM pure tungsten were adopted and reported by Li et al. [20] and Ivekovi´c et al. [21]. Their results showed that the addition of secondary-phase nanoparticles or Tantalum could reduce cracks in the process of SLM pure tungsten, but a crack-free sample was still not available. In addition, the addition of low-melting-point metals might be beneficial to the fabrication of crack-free tungsten alloy components. Li et al. [22] investigated the fabrication of W-10Cu by SLM and obtained an optimized combination of laser power and scan speed. Their results showed that the forming mechanism of SLM W-10Cu was liquid phase sintering. Ivekovi´c et al. [23] obtained a 90W-7Ni-3Fe sample with a high relative density (>95%). Their results indicated that the high densification of 90W-7Ni-3Fe samples required a high energy density. In addition, they observed three major binding mechanisms: liquid phase sintering, partial melting, and complete melting. Preheating contributes to complete melting. After heat treatment, the tensile strength decreased slightly, but the elongation was significantly improved. Li et al. [24] studied the e ffect of process parameters on the densification and microstructure of 90W-7Ni-3Fe in SLM. They found that a lower scan speed, narrower scan interval, and thinner layer thickness can improve the densification process. Similar findings were also reported by Zhang et al. [25], who established an e ffective 3D model based on finite element analysis theory and temperature distributions under di fferent process parameters. As mentioned above, tungsten and its alloys are of interest to researchers, but SLM 90W-7Ni-3Fe has been rarely discussed.

In this work, 90W-7Ni-3Fe samples were formed by SLM. The influences of the process parameters on the densification, phase constitution, and microhardness of the 90W-7Ni-3Fe samples were discussed. In addition, the microstructure and tensile properties of the 90W-7Ni-3Fe samples fabricated by SLM were investigated and discussed.

## **2. Materials and Methods**

#### *2.1. Experimental Equipment and Preparation*

All experiments were carried out with an SLM 280 HL (SLM solutions, Germany), equipped with two 400 W Nd: YAG lasers. Figure 1a depicts the schematic diagram of SLM 280 HL. SLM 280 HL has two kinds of substrates: 250 mm × 250 mm and 100 mm × 100 mm. A small substrate was utilized in this work. During the process of SLM, tungsten heavy alloy powder particles fell from the powder container under gravity, and then the fallen powder particles were evenly spread on the substrate under the action of a powder scraper. The bi-directional movement of the powder scraper was adopted for the sake of enhancing the building e fficiency. All samples with a size of 10 mm × 10 mm × 5 mm were prepared on a 304 stainless steel substrate, which was preheated at 150 ◦C in order to prevent cracking and warping. In the whole SLM process, the chamber was filled with argon in order to avoid oxidation, and the content of oxygen was kept below 400 ppm. Figure 1b illustrates the building process of the SLM tungsten heavy alloy.

**Figure 1.** (**a**) Schematic diagram of selective laser melting (SLM) equipment; (**b**) the building process of the SLM.