gestational diabetes mellitus ( gdm ) identifies women with an increased risk of developing type 2 diabetes and cardiovascular disease .
therefore , women with prior gdm ( pgdm ) are recommended to regularly undergo assessment of glucose tolerance   in order to detect overt diabetes in time to initiate treatment to prevent complications .
the current view of gdm pathophysiology is that women who develop gdm are characterized by  beta - cell dysfunction based on chronic insulin resistance  .
consequently , disturbances in glucose metabolism are thought to be of chronic nature rather than of acute onset during pregnancy .
we have previously shown that pgdm with metabolic deterioration within five years after delivery are characterized by hyperglycemia , insulin resistance , and hyperinsulinemia ; furthermore first - phase insulin secretion was impaired in these women compared to pgdm who did not experience deterioration of glucose tolerance .
in addition , while those pgdm who progress to diabetes have a marked increase in glycemia and insulin resistance before diabetes onset , we observed that beta - cell function declines continuously over years .
others have shown that declining beta - cell compensation for increased insulin resistance ( estimated by the disposition index ) characterizes pgdm who convert to overt diabetes within 12 years after delivery   and that this decline was associated with an increase in body weight and c - reactive protein ( crp ) as well as a decrease in adiponectin .
approximately 50% of pgdm develop type 2 diabetes within the first five years after delivery [ 8 , 9 ] . at the same time
, there is a group of pgdm who are able to maintain normal glucose tolerance within this vulnerable period of metabolic deterioration .
although many studies describe metabolic changes in those who convert to diabetes , less is known about pgdm who are able to maintain normal glucose tolerance ( ngt ) over the years following delivery .
it could be speculated that metabolic disturbances are cured in those pgdm and that their risk of developing diabetes equals the one of women without a history of gdm .
consequently , time- and cost - consuming follow - ups would not be necessary in these women .
this could help to reduce unnecessary costs . since data that would answer this question are scare , the aim of this study was to compare validated parameters of insulin sensitivity and secretion between pgdm with ngt five years after gestational diabetes and healthy controls ( five years after normal pregnancy ) .
in addition , metabolic changes in pgdm within the five - year observational period and the impact of weight loss within this time were investigated .
the current study was part of the viennese post - gestational diabetes project ( vpgdp ) , a prospective longitudinal study in women with a history of gdm .
pgdm were recruited during a pregnancy complicated by gdm in the diabetes outpatient clinic of the division of endocrinology and metabolsim of the medical university of vienna , where they had been seen during pregnancy .
the human ethics committee of the medical university of vienna approved the protocol and all women gave written informed consent .
exclusion criteria were age  18 years , known preexisting glucose intolerance ( impaired glucose tolerance , type 1 or type 2 diabetes ) , diagnosis of gdm before the 8th gestational week , positive diabetes - associated antibodies ( assessed during and after pregnancy at our division ) , ethnicity other than caucasian , morbid obesity ( pregestational body mass index > 40  kg / m ) , or evidence of chronic diseases , including kidney or liver diseases and chronic inflammatory diseases . in con , exclusion criteria additionally included the existence of any risk factors for diabetes ( i.e. , positive family history or chronic medication known to influence carbohydrate metabolism ) .
for the current study , 45 pgdm with normal glucose tolerance at five - year follow - up and 18 healthy controls were matched for age and body mass index ( table 1 ) .
data from the visit 5 years postpartum were compared between the groups and in pgdm also to the baseline examination ( six months after delivery ) .
furthermore , an additional subanalysis was performed , in which those pgdm with weight loss of 7% ( wihtin the 5-year observational period ) were compared to the healthy control group .
this range was chosen in regard to the american diabetes association ( ada ) recommendation of 7% weight loss in patients with prediabetes .
all women received dietary counseling and were recommended to regain normal body weight by intake of a healthy diet and regular physical activity .
glucose tolerance tests were scheduled between day 3 and day 10 of their menstrual cycle , performed in the morning after an overnight fast of at least 8 hours .
women were asked to refrain from physical activity 3 days prior to the follow - up visits .
all women underwent an oral glucose tolerance test ( ogtt ) and the majority underwent also an intravenous glucose tolerance test ( 76% of pgdm and 61% of con ) .
reasons for not undergoing an intravenous glucose tolerance test ( ivgtt ) were mainly problems in time scheduling ( additional appointment according to menstrual cycle , more than 2 weeks after ogtt ) .
after a venous catheter was placed into an antecubital vein , blood samples for the measurement of glucose , insulin , and c - peptide were taken at fasting as well as 10 , 20 , 30 , 60 , 90 , 120 , 150 , and 180 minutes after ingestion of 75  g glucose in a solution .
for the ivgtt , one venous catheter for blood sampling was placed in one antecubital vein and another one for intravenous administration of glucose and insulin in an antecubital vein of the other arm .
blood samples ( for measurement of glucose , insulin , and c - peptide ) were drawn at the fasting state ( 10 and 0 minutes ) and 3 , 4 , 5 , 6 , 8 , 10 , 14 , 19 , 22 , 27 , 30 , 35 , 40 , 50 , 70 , 100 , 140 , and 180 minutes after injection of glucose ( 300  mg / kg body weight ) . at 20 minutes , normal insulin ( humulin r , eli lilly , indianapolis ,
in , usa ) was given with a concentration of 0.03  iu / kg body weight and for a duration of 5 minutes .
serum samples for the assessment of insulin and c - peptide were immediately cooled down , centrifuged , stored at 20 degrees celsius , and later analyzed in the lab of the division of endocrinology and metabolism by commercially available radioimmunoassay kits : insulin ( serono diagnostics , freiburg , germany ) and c - peptide ( cis bio international , cedex , france ) with interassay coefficients of variation of < 5% . at fasting , additional blood samples were taken and the following parameters were assessed : adiponectin was measured in duplicate by an elisa system developed for the assessment of human plasma adiponectin concentrations ( department of internal medicine and molecular science , osaka university , suita , osaka , japan ) .
charles , mo , usa ) and glucagon ( icn biomedicals , costa mesa , ca , usa ) were measured in duplicate by commercially available radioimmunoassay kits with a cv < 6% for leptin and < 8% for glucagon .
hba1c ( by high - performance liquid chromatography , given in % ) , tsh , total cholesterol , ldl - cholesterol , hdl - cholesterol , triglycerides , and c - reactive protein   were measured by established methods in the central lab of the medical university of vienna . normal glucose tolerance ( ngt )
was defined according to the criteria of the ada : fasting plasma glucose ( fpg ) < 100  mg / dl and 2-hour post - ogtt glucose < 140  mg / dl . the oral glucose insulin sensitivity ( ogis ) index describes glucose clearance per unit change of insulin concentration .
parameters of insulin secretion were described by the areas under the curve ( auc ) of insulin and c - peptide during ogtt and ivgtt , calculated with the trapezoidal rule .
hepatic insulin extraction ( hie , given in % ) was quantified with a mathematical model of insulin / c - peptide interactions . from ivgtt ,
insulin sensitivity index ( si , in 10  min/(u / ml ) ) describing insulin effect on glucose disappearance   was computed .
first - phase insulin secretion was assessed by airg calculated by averaging insulin concentrations above basal from 3 to 10 minutes and given in u / ml . the disposition index derived from ivgtt ( 10  min ) was calculated as si  airg and describes the combined effect of insulin secretion and sensitivity on glucose disposal ; it is frequently used to describe the ability of the beta cells to adapt for increased insulin resistance . between group differences
were calculated by anova ; changes between baseline and follow - up visit in pgdm were calculated by a paired t - test .
sas software ( enterprise guide 4.3 , sas institute inc . , cary , nc , usa ) was used for all computations .
five years after the index pregnancy , pgdm  despite normal glucose tolerance  had significantly higher levels of plasma glucose at fasting as well as 60 minutes of the ogtt compared to con ; in line , the auc of glucose was significantly increased in pgdm compared to con ( figure 1 ) .
insulin sensitivity , derived by ogis , was decreased in pgdm compared to con ( figure 2(a ) ) .
furthermore , adiponectin was lower in pgdm ( figure 2(b ) ) , while blood pressure , leptin , glucagon , tsh , and lipid profile did not differ between the groups .
pgdm had significantly higher waist circumference ( figure 2(c ) ) as well as crp concentrations , ( figure 2(d ) ) .
normal body weight , defined as bmi < 25  kg / m , was found in 30 out of 45 pgdm ( = 66.7% ) and in 14 out of 18 con ( = 77.8% ) .
insulin sensitivity ( ogis ) was negatively correlated with bmi and body weight in the whole study group ( bmi : r = 0.3 , p = 0.01 ; body weight : r = 0.3 , p = 0.02 ) . when follow - up data in pgdm were compared to their baseline examination (= six months postpartum ) , waist circumference ( 85.5  9.0 versus 81.8  9.8  cm , p = 0.002 ) and diastolic blood pressure ( 76.7  9.1 versus 72.5  9.4  mmhg , p < 0.04 ) were lower at five - year follow - up compared to baseline ( 6 months after pregnancy ) .
in addition , pgdm had significantly lower total cholesterol ( from 211.9  48.6 to 198.4  40.2  mg / dl , p < 0.006 ) and ldl - cholesterol ( from 134.2  45.4 to 122.6  37.0  mg / dl , p = 0.002 ) compared to baseline .
no change was observed in body weight , hba1c , glucagon , leptin , or tsh .
furthermore , the disposition index ( 1.7  1.2 versus 2.6  2.3 10min , p < 0.004 ) and insulin sensitivity derived from ivgtt ( from 4.3  2.5 to 6.3  3.2 10min/(u / ml ) , p = 0.001 ) were increased compared to baseline .
twelve pgdm had significant weight loss ( 7% ) within the 5-year observational period ( pgdm_wl ) and were compared to con , in order to assess whether weight loss was associated with an improved metabolic profile . while there was no difference in age , bmi , and waist circumference between the groups , pgdm_wl had significantly increased concentrations of glucose ( auc of glucose , 1.13  0.16 versus 1.0  0.12  mol /
l  min , p < 0.02 ) and insulin during the ogtt ( tis : 27.1  7.1 versus 21.8  5.7  nmol / l , p = 0.03 , auc of c - peptide : 419.5  106.9 versus 347.0  81.3 
nmol / l  min , p = 0.04 ) , whereas insulin sensitivity was lower compared to con ( ogis : 466.9  46.4 versus 510.6  53.1  ml / min  m , p < 0.03 ) .
furthermore , crp was higher in pgdm_wl compared to con ( 0.4  0.3 versus 0.2  0.2  mg / dl , p = 0.04 ) . when pgdm_wl were compared to their baseline state , the significant changes in body weight ( 9.9  4.8  kg , bmi : from 26.8  3.5 to 23.2  2.5  kg / m , both p < 0.0001 ) and waist- ( from 89.0  7.9 to 79.8  9.4  cm , p = 0.0002 ) and hip - circumference ( from 107.5  5.8 to 97.8  4.6  cm , p <
0.0001 ) were accompanied by an improved disposition index ( from 1.6  1.0 to 2.9  1.6 10  min , p = 0.01 ; in line with the whole pgdm - group ) , a decline in crp concentrations ( from 0.6  0.2 to 0.4  0.3  mg / dl , p = 0.03 ) , diastolic blood pressure ( from 80.8  9.3 to 72.2  7.9  mmhg , p = 0.02 ) , and leptin ( from 17.7  5.5 to 14.5  7.0  ng / ml , p < 0.03 ) .
the current study aimed to assess whether disturbances in glucose metabolism can be observed in women with prior gestational diabetes ( pgdm ) who were able to maintain normal glucose tolerance ( ngt ) until five years after a gdm - pregnancy . according to our data ,
pgdm  despite normal glucose tolerance  were still characterized by decreased insulin sensitivity and increased glucose concentrations during the ogtt compared to healthy controls .
furthermore , crp levels and waist circumference were higher in pgdm compared to con , despite comparable bmi , while adiponectin was decreased in pgdm .
in addition , pgdm with weight loss  7% within the five - year follow - up period exhibited pronounced metabolic disturbances compared to con .
insulin resistance is a frequent finding in women with prior gestational diabetes and associated with ectopic lipid accumulation in skeletal muscle and liver [ 20 , 21 ] .
it is assumed that gestational diabetes develops on the background of chronic insulin resistance , aggravated by the physiological insulin resistance of late pregnancy [ 2 , 3 ] . according to our observations
, we also assume that insulin resistance in pgdm is of chronic nature and the diagnosis of gdm during pregnancy detects a metabolic phenotype with increased insulin resistance in a young female cohort .
we found a weak , but significant , inverse association between bmi and insulin sensitivity ; however , also in the subgroup of pgdm with significant weight loss ( pgdm_wl ) insulin sensitivity was significantly lower compared to the healthy control group .
special attention has to be given to this subgroup of pgdm who had significant weight loss of 7% within the follow - up period .
this group had a bmi of approximately 27  kg / m six months after delivery and
weight loss in this group was accompanied by a reduction in waist- and hip - circumferences as well as leptin ; furthermore , the disposition index ( in line with the whole study group ) improved ; however , despite marked changes in body weight , insulin sensitivity and glucose concentrations during the ogtt and ivgtt remained unchanged compared to the baseline examination ( 6 months postpartum ) .
hence , it might be speculated that obesity is not the main reason for insulin resistance in pgdm .
this assumption is supported by one of our prior observations , which showed that insulin resistance is pronounced in lean subjects with gdm and persists after delivery .
in addition , it is in line with prior investigations in women with a history of gdm showing that the decline in insulin sensitivity and beta - cell compensation could not be explained by changes in adiposity . it has also been shown that impaired beta - cell glucose sensitivity independent of obesity and hyperglycemia displays a risk factor in pgdm .
it has to be noted that the majority of women in our study groups ( 66.7% in pgdm and 77.8% in con ) had a bmi lower than 25  kg / m and thus fulfill the criteria of normal body weight .
furthermore , mean waist circumference in pgdm was 81.8  cm , which would fulfill the who criteria for metabolic syndrome , but not those of the us national cholesterol education program adult treatment panel iii .
this again leads us to conclude that obesity might not be the main trigger of glucose intolerance in this young female cohort or not in all pgdm .
the observation that glucose concentrations during the ogtt were higher in pgdm compared to con clearly indicates a risk of hyperglycemia in these women .
this risk would not have been detected by simply concentrating on the definition of ngt , because glucose values were within the normal range ; however , in comparison to age- and bmi - matched controls , glucose concentrations during the ogtt were significantly higher in pgdm . and
even in pgdm_wl , the significant weight loss did not counteract increased glucose concentrations compared to con .
the finding that adiponectin was decreased and crp increased in pgdm compared to con is of great interest . a recent study by xiang and coworkers [ 6 , 7 ] described that declining beta - cell compensation in pgdm ( described by the disposition index ) is  besides weight gain  associated with declining levels of adiponectin and rising crp levels . to our surprise , these metabolic features were also observed in our group of pgdm who were able to maintain normal glucose tolerance within this vulnerable period of five years postpartum .
hence , the question of whether these metabolic alterations can be used as markers of metabolic deterioration or simply reflect this special metabolic profile in pgdm appears .
specifically a drop in adiponectin could reflect metabolic deterioration in pgdm and indicate the need for closer follow - up of these women ; however , this assumption has to be reexamined in future prospective studies .
chronic inflammation and hypoadiponectinemia are frequently found in patients with diabetes ; hence it appears that these disturbances could be the cause rather than the consequences of insulin resistance and hyperglycemia .
in addition , this combination of hypoadiponectinemia and increased crp might contribute to the development of atherosclerosis [ 26 , 27 ] .
hence , we could assume that pgdm despite normal glucose tolerance have an increased cardiovascular risk and should be considered as high - risk population for cardiovascular disease .
several metabolic parameters , that is , ldl - cholesterol , diastolic blood pressure , and waist circumference as well as the disposition index and insulin sensitivity derived from ivgtt , were improved in pgdm at five years postpartum compared to baseline . but
despite these ameliorations and the fact that the majority of our pgdm group were able to regain / maintain normal body weight and normal glucose tolerance , disturbances in glucose regulation were observed .
hence , it appears that the metabolic profile and thus the risk of developing type 2 diabetes seem to be chronic and that gdm only identifies women at risk .
it appears that the pivotal mechanisms that finally lead to the development of overt hyperglycemia in pgdm have not been elucidated in detail .
this may include a genetic disposition in this group of gdm without obesity but still increased risk for type 2 diabetes .
as shown , gdm risk is associated with genes involved in the regulation of insulin secretion .
at least , more studies are needed to better understand the development of overt hyperglycemia and develop treatment strategies , which can improve prevention .
while the strength of the current study lies in the investigation of a well - characterized cohort and performance of validated tests under dynamic  not only fasting  conditions , it also has some limitations : the study group is quite small and follow - up is limited to five years ; an extended follow - up period could allow strengthening our conclusions .
consequently we can summarize that metabolic disturbances which predispose pgdm to the development of overt diabetes appear to be chronic and can be hidden but , still , remain life - long and therefore regular follow - ups should be recommended to all women with a history of gdm in order to detect diabetes in time and prevent complications , especially the onset of cardiovascualr disease .
 
 background . the study aimed to assess whether women with prior gestational diabetes ( pgdm ) , despite maintenance of normal glucose tolerance ( ngt ) 
 five years after delivery , display metabolic disturbances compared to healthy controls . methods . 
 45  pgdm with ngt were compared to 18 women without a history of gdm ( con ) , matched for age ( 37.0    4.1 versus 35.2    5.3 , p = ns ) and bmi ( 24.3    3.1 versus 23.3    3.3 , p = ns ) . 
 metabolic parameters were derived from oral and intravenous glucose tolerance tests ; furthermore lipid profile , c - reactive protein ( crp ) , adiponectin , leptin , and glucagon were assessed . 
 results . 
 five years postpartum , pgdm had increased glucose concentrations during the ogtt ( auc : 1.12    0.15 versus 1.0    0.12  mol / l  min , p = 0.003 ) and insulin sensitivity was decreased compared to con ( ogis : 467.2    64.1 versus 510.6    53.1  ml / min  m2 , p = 0.01 ) . 
 pgdm had lower adiponectin ( 8.1    2.6 versus 12.6    5.3 , p < 0.008 ) but increased waist circumference and crp compared to con . 
 conclusions . despite diagnosis of normal glucose tolerance , 
 pgdm are characterized by hyperglycemia and insulin resistance compared to healthy controls , accompanied by decreased adiponectin and increased crp concentrations , thus linking metabolic disturbances to an increased cardiovascular risk in pgdm . 
1. Background
2. Study Population and Methods
3. Results
4. Discussion