preterm birth preterm birth preterm birth, also known as premature birth, is the birth of a baby at fewer than 37 weeks gestational age, as opposed to full-term delivery at approximately 40 weeks. extreme preterm is less than 28 weeks, very early preterm birth is between 28 and 32 weeks, early preterm birth occurs between 32 and 36 weeks, late preterm birth is between 34 and 36 weeks' gestation. these babies are also known as premature babies or colloquially preemies (american english) or premmies (australian english). symptoms of preterm labor include uterine contractions which occur more often than every ten minutes and/or the leaking of fluid from the vagina before 37 weeks. premature infants are at greater risk for cerebral palsy, delays in development, hearing problems and problems with their vision. the earlier a baby is born, the greater these risks will be. preterm birthother namespremature birth, preemies, premmiesintubated preterm baby in an incubatorspecialtyneonatology, pediatrics, obstetricssymptomsbirth of a baby at younger than 37 weeks' gestational agecomplicationscerebral palsy, delays in development, hearing problems, sight problemscausesoften unknownrisk factorsdiabetes, high blood pressure, multiple gestation, obesity or underweight, a number of vaginal infections, celiac disease, tobacco smoking, psychological stresspreventionprogesteronetreatmentcorticosteroids, keeping the baby warm through skin-to-skin contact, supporting breastfeeding, treating infections, supporting breathingfrequency~15 million a year (12% of deliveries)deaths805,800 the cause of spontaneous preterm birth is often not known. risk factors include diabetes, high blood pressure, multiple gestation (being pregnant with more than one baby), being either obese or underweight, vaginal infections, air pollution exposure, tobacco smoking, and psychological stress. for a healthy pregnancy, medical induction of labor or cesarean section are not recommended before 39 weeks unless required for other medical reasons. there may be certain medical reasons for early delivery such as preeclampsia. preterm birth may be prevented in those at risk if the hormone progesterone is taken during pregnancy. evidence does not support the usefulness of bed rest. it is estimated that at least 75% of preterm infants would survive with appropriate treatment, and the survival rate is highest among the infants born the latest in gestation. in women who might deliver between 24 and 37 weeks, corticosteroid treatment may improve outcomes. a number of medications, including nifedipine, may delay delivery so that a mother can be moved to where more medical care is available and the corticosteroids have a greater chance to work. once the baby is born, care includes keeping the baby warm through skin-to-skin contact or incubation, supporting breastfeeding and/or formula feeding, treating infections, and supporting breathing. preterm babies sometimes require intubation. preterm birth is the most common cause of death among infants worldwide. about 15 million babies are preterm each year (5% to 18% of all deliveries). late preterm birth accounts for 75% of all preterm births. this rate is inconsistent across countries. in the united kingdom 7.9% of babies are born pre-term and in the united states 12.3% of all births are before 37 weeks gestation. approximately 0.5% of births are extremely early periviable births (20–25 weeks of gestation), and these account for most of the deaths. in many countries, rates of premature births have increased between the 1990s and 2010s. complications from preterm births resulted in 0.81 million deaths in 2015, down from 1.57 million in 1990. the chance of survival at 22 weeks is about 6%, while at 23 weeks it is 26%, 24 weeks 55% and 25 weeks about 72%. the chances of survival without any long-term difficulties are lower. signs and symptoms a new mother holds her premature baby at kapiolani medical center nicu in honolulu, hawaii. signs and symptoms of preterm labor include four or more uterine contractions in one hour. in contrast to false labour, true labor is accompanied by cervical dilation and effacement. also, vaginal bleeding in the third trimester, heavy pressure in the pelvis, or abdominal or back pain could be indicators that a preterm birth is about to occur. a watery discharge from the vagina may indicate premature rupture of the membranes that surround the baby. while the rupture of the membranes may not be followed by labor, usually delivery is indicated as infection (chorioamnionitis) is a serious threat to both fetus and mother. in some cases, the cervix dilates prematurely without pain or perceived contractions, so that the mother may not have warning signs until very late in the birthing process. causes the main categories of causes of preterm birth are preterm labor induction and spontaneous preterm labor. risk factors the exact cause of spontaneous preterm birth is difficult to determine and it may be caused by many different factors at the same time as labor is a complex process. four different pathways have been identified that can result in preterm birth and have considerable evidence: precocious fetal endocrine activation, uterine overdistension (placental abruption), decidual bleeding, and intrauterine inflammation or infection. identifying women at high risk of giving birth early would enable the health services to provide specialized care for these women and their babies, for example a hospital with a special care baby unit such as a neonatal intensive care unit (nicu). in some instances, it may be possible to delay the birth. risk scoring systems have been suggested as an approach to identify those at higher risk, however, there is no strong research in this area so it is unclear whether the use of risk scoring systems for identifying mothers would prolong pregnancy and reduce the numbers of preterm births or not. maternal factors risk factorrelative risk95% confidence interval fetal fibronectin4.02.9–5.5 short cervical length2.92.1–3.9 prenatal care absent2.92.8–3.0 chlamydia2.21.0–4.8 low socio-economic status1.91.7–2.2 large or small pregnancy weight gain1.81.5–2.3 short maternal height1.81.3–2.5 periodontitis1.61.1–2.3 celiac disease1.41.2–1.6 asymptomatic bacteriuria1.10.8–1.5 high or low bmi0.960.66–1.4 odds ratio history of spontaneous preterm birth3.63.2–4.0 bacterial vaginosis2.21.5–3.1 black ethnicity/race2.01.8–2.2 filipino ancestry1.71.5–2.1 unwanted pregnancy: 1 1.51.41-1.61 unintended pregnancy: 1 1.311.09-1.58 being single/unmarried1.21.03–1.28 percentage premature births in england and wales 2011, by age of mother and whether single or multiple birth risk factors in the mother have been identified that are linked to a higher risk of a preterm birth. these include age (either very young or older), high or low body mass index (bmi), length of time between pregnancies, previous spontaneous (i.e., miscarriage) or surgical abortions, unintended pregnancies, untreated or undiagnosed celiac disease, fertility difficulties, heat exposure, and genetic variables. studies on type of work and physical activity have given conflicting results, but it is opined that stressful conditions, hard labor, and long hours are probably linked to preterm birth. obesity does not directly lead to preterm birth; however, it is associated with diabetes and hypertension which are risk factors by themselves. to some degree those individuals may have underlying conditions (i.e., uterine malformation, hypertension, diabetes) that persist. couples who have tried more than one year versus those who have tried less than one year before achieving a spontaneous conception have an adjusted odds ratio of 1.35 (95% confidence interval 1.22–1.50) of preterm birth. pregnancies after ivf confers a greater risk of preterm birth than spontaneous conceptions after more than one year of trying, with an adjusted odds ratio of 1.55 (95% ci 1.30–1.85). certain ethnicities may have a higher risk as well. for example, in the u.s. and the uk, black women have preterm birth rates of 15–18%, more than double than that of the white population. many black women have higher preterm birth rates due to multiple factors but the most common is high amounts of chronic stress, which can eventually lead to premature birth. adult chronic disease is not always the case with premature birth in black women, which makes the main factor of premature birth challenging to identify. filipinos are also at high risk of premature birth, and it is believed that nearly 11–15% of filipinos born in the u.s. (compared to other asians at 7.6% and whites at 7.8%) are premature. filipinos being a big risk factor is evidenced with the philippines being the eighth-highest ranking in the world for preterm births, the only non-african country in the top 10. this discrepancy is not seen in comparison to other asian groups or hispanic immigrants and remains unexplained. genetic make-up is a factor in the causality of preterm birth. genetics has been a big factor into why filipinos have a high risk of premature birth as the filipinos have a large prevalence of mutations that help them be predisposed to premature births. an intra- and transgenerational increase in the risk of preterm delivery has been demonstrated. no single gene has been identified. marital status is associated with risk for preterm birth. a study of 25,373 pregnancies in finland revealed that unmarried mothers had more preterm deliveries than married mothers (p=0.001). pregnancy outside of marriage was associated overall with a 20% increase in total adverse outcomes, even at a time when finland provided free maternity care. a study in quebec of 720,586 births from 1990 to 1997 revealed less risk of preterm birth for infants with legally married mothers compared with those with common-law wed or unwed parents. factors during pregnancy medications during pregnancy, living conditions, air pollution, smoking, illicit drugs or alcohol, infection, or physical trauma may also cause a preterm birth. air pollution: living in an area with a high concentration of air pollution is a major risk factor for preterm labor, including living near major roadways or highways where vehicle emissions are high from traffic congestion or are a route for diesel trucks that tend to emit more pollution. the use of fertility medication that stimulates the ovary to release multiple eggs and of ivf with embryo transfer of multiple embryos has been implicated as a risk factor for preterm birth. often labor has to be induced for medical reasons; such conditions include high blood pressure, pre-eclampsia, maternal diabetes, asthma, thyroid disease, and heart disease. certain medical conditions in the pregnant mother may also increase the risk of preterm birth. some women have anatomical problems that prevent the baby from being carried to term. these include a weak or short cervix (the strongest predictor of premature birth). women with vaginal bleeding during pregnancy are at higher risk for preterm birth. while bleeding in the third trimester may be a sign of placenta previa or placental abruption—conditions that occur frequently preterm—even earlier bleeding that is not caused by these conditions is linked to a higher preterm birth rate. women with abnormal amounts of amniotic fluid, whether too much (polyhydramnios) or too little (oligohydramnios), are also at risk. anxiety and depression have been linked as risk factors for preterm birth. the use of tobacco, cocaine, and excessive alcohol during pregnancy increases the chance of preterm delivery. tobacco is the most commonly used drug during pregnancy and contributes significantly to low birth weight delivery. babies with birth defects are at higher risk of being born preterm. passive smoking and/or smoking before the pregnancy influences the probability of a preterm birth. the world health organization published an international study in march 2014. presence of anti-thyroid antibodies is associated with an increased risk preterm birth with an odds ratio of 1.9 and 95% confidence interval of 1.1–3.5. intimate violence against the mother is another risk factor for preterm birth. physical trauma may case a preterm birth. the nigerian cultural method of abdominal massage has been shown to result in 19% preterm birth among women in nigeria, plus many other adverse outcomes for the mother and baby. this ought not be confused with massage therapy conducted by a fully trained and certified/licensed massage therapist or by significant others trained to provide massage during pregnancy, which—in a study involving pregnant females with prenatal depression—has been shown to have numerous positive results during pregnancy, including the reduction of preterm birth, less depression, lower cortisol, and reduced anxiety. in healthy women, however, no effects have been demonstrated in a controlled study. infection the frequency of infection in preterm birth is inversely related to the gestational age. mycoplasma genitalium infection is associated with increased risk of preterm birth, and spontaneous abortion. infectious microorganisms can be ascending, hematogenous, iatrogenic by a procedure, or retrograde through the fallopian tubes. from the deciduae they may reach the space between the amnion and chorion, the amniotic fluid, and the fetus. a chorioamnionitis also may lead to sepsis of the mother. fetal infection is linked to preterm birth and to significant long-term