To examine whether there was a difference in weight gain by the severity of GDM, we evaluated maternal weight gain by 24 weeks of gestation in individuals requiring insulin therapy (A2 GDM) compared with those who were diet- or exercise-controlled or both (A1 GDM). There were no significant differences in age, race, or parity among the individuals classified as A1 compared with A2 GDM and controls. Participants in the A1 GDM group had significantly lower prepregnancy BMI compared with those in the A2 GDM group (28.8 compared with 33.6) but had no difference in 1-hour glucose tolerance test or gestational age at delivery. Weight gain at 24 weeks in A1 GDM, A2 GDM, and control groups is presented in Figure 2. Compared with controls, both diet- and insulin-requiring GDM participants had significantly greater mean weight gain at 24 weeks of gestation (A1 GDM compared with controls, P<.027; A2 GDM compared with controls, P<.019). However, no difference was found in mean weight gain when comparing participants classified as A1 GDM compared with A2 GDM (P=.942) or when comparing A1 GDM and A2 GDM individuals based on prepregnancy BMI.
Because some women will lose weight over the course of early pregnancy, we compared the GDM and control groups according to different gestational weight gain categories. We categorized total maternal gestational weight gain achieved by 24 weeks of gestation into four groups: those who lost weight and those who gained 0–10 lb, 11–20 lb, and more than 20 lb. Figure 3 presents the frequency of cases and controls for each weight gain category. A relatively greater percentage of normal glucose tolerance patients lost weight or gained less than 10 lb (P=.029) in the first two trimesters. We found the GDM patients had more often gained 11–20 lb or more than 20 lb (P=.006). Among the weight gain categories, there were significant differences in race (P=.047), maternal age (P<.001), and prepregnancy BMI (P<.001), with African Americans, older patients, and those with a lower prepregnancy BMI tending to gain more by 24 weeks of gestation. There was no difference in parity, delivery type, or gestational age at delivery. When comparing the frequency of patients with either A1 GDM or A2 GDM by using our different maternal weight gain categories, we found no differences in the percentage who lost weight or gained 0–10, 11–20, or more than 20 lb.
Last, we examined whether remaining in the recent IOM guidelines for gestational weight gain was related to the development of GDM. The IOM recommended gaining 1.1–4.4 lb in the first trimester and 10.4–13 lb for normal-weight, 6.5–9.1 for overweight, and 5.2–7.8 lb for obese women in the second trimester.14 We found no significant difference among the controls and GDM patients who remained within the guidelines or gained outside the recommendations.
We found a significant difference between GDM and controls in gestational weight gain at 24 weeks of gestation. When examined by BMI category, this difference was significant only for overweight and obese patients. Additionally, both A1 and A2 GDM patients had higher gestational weight gain compared with controls.
Nearly two thirds of adult women in the United States are currently overweight or obese.14 Although the IOM recently revised its pregnancy weight-gain recommendations,15 50–60% of women will have total pregnancy weight gain above these targets, placing themselves and their children at increased risk for complications during and after pregnancy.16
Our study suggests that increased maternal gestational weight gain in the first and second trimesters of pregnancy may affect glucose metabolism and GDM development in overweight and obese women. Gestational weight gain early in pregnancy is often related to increased plasma volume; however, accrual of adipose tissue begins around 12–14 weeks in overweight and obese women and potentially earlier in underweight and normal-weight women.17 Gestational diabetes mellitus develops when pancreatic beta cell function cannot compensate sufficiently to maintain normoglycemia in the face of increased insulin resistance. Because overweight and obese women have increased insulin resistance before conception, the increase in gestational weight gain by 24 weeks may “push them over the edge” toward GDM development. Among nonpregnant Pima Indians, insulin resistance was associated with lower rates of weight gain.18 Weight gain in early pregnancy has also been shown to be inversely proportional to changes in insulin sensitivity.19
Previous studies, all retrospective, reported an association between increased gestational weight gain and pregnancy complications including hypertensive disorders and GDM among normal-weight20 and overweight21 women, but not for morbidly obese patients.22 Two smaller investigations did not find associations between “excessive mid-trimester weight gain” and abnormal glucose tolerance test results.10,23 However, in a cohort of 5,131 women an increase in BMI category from normal weight to overweight or overweight to obese was associated with an increased risk of GDM.24 Several other studies have also found an association between gestational weight gain and an abnormal 50-g oral glucose tolerance test, especially in overweight and obese white, African American, and Hispanic women.11,25,26 Finally, a recent nested case-control study from California reported that first-trimester weight gain was associated with GDM development. When controlling for prepregnancy BMI in multivariate analysis, the overweight women who gained in the highest tertile were nearly twice as likely to develop GDM compared with those in the lowest tertile.27
These findings are of particular importance given the rising prevalence of overweight and obese women of childbearing age. Obesity itself is associated with a 3–5 times increased odds ratio of developing GDM.28 Interestingly, our data failed to identify a relationship between recommended compared with excessive weight gain on the basis of IOM recommendations15 and the diagnosis of GDM. Given the long-term health implications of GDM on future maternal and fetal cardiovascular health,28 identifying potential areas of prevention may have far-reaching benefits. To date there is no consensus regarding optimal lifestyle modification in obese patients showing consistently improved pregnancy outcomes, including incidence of GDM.29
Our study has several limitations. As a chart review, this study is open to ascertainment bias and is further limited by what data were available in the medical records. The entire cohort was drawn from over several years (2000–2007) to appropriately match 3:1 to GDM. Although the GDM definition and management protocols and the official recommendations for gestational weight gain in pregnancy did not change during that time, individual practice variations may have affected our outcomes. In addition, similar to many other studies, reliable pregravid weights were not available on the participants, so self-reported prepregnancy weights were used. On average patients tend to underestimate their weight, especially overweight and obese patients30–32; however, as the weights for both case and control groups were self-reported, this would bias the results only toward the null.33 To further reduce the bias, the documented weight gain between 12 and 24 weeks of gestational age was also compared between groups. Our study population was also nearly 80% overweight or obese with an increase in 0.74 m/kg2 of BMI over time,34 more than the national overweight and obesity rate but reflective of our typical GDM patient population. Importantly, our study has several strengths. As a matched case-control study, the influence of potential confounding variables such as prepregnancy BMI, race, age, and parity is reduced. Further, we examined gestational weight gain only until the time of diagnosis of GDM, thus avoiding the confounding effect of GDM treatment on gestational weight gain.
In summary, we examined gestational weight gain early in pregnancy in relation to developing GDM stratified by prepregnancy BMI. Gestational weight gain before 24 weeks of gestation was significantly higher among patients with GDM than in normal glucose tolerance control individuals, specifically in the overweight and obese patients.
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