Objective
We sought to examine associations between gestational weight gain according to the 2009 Institute of Medicine (IOM) guidelines and perinatal outcomes in overweight/obese women with type 2 diabetes mellitus (T2DM).
Study Design
This is a retrospective cohort study of 2310 women with T2DM enrolled in the California Diabetes and Pregnancy Program. Gestational weight gain was categorized by 2009 IOM guidelines. Perinatal outcomes were assessed using the χ 2 test and multivariable logistic regression analysis.
Results
With excessive gestational weight gain, the odds of having large-for-gestational age (adjusted odds ratio [aOR], 2.00; 95% confidence interval [CI], 1.33–3.00) or macrosomic (aOR, 2.59; 95% CI, 1.56–4.30) neonates and cesarean delivery (aOR, 1.47; 95% CI, 1.03–2.10) was higher. Women with excessive gestational weight gain per week had increased odds of preterm delivery (aOR, 1.57; 95% CI, 1.11–2.20).
Conclusion
In overweight or obese women with T2DM, gestational weight gain greater than the revised IOM guidelines was associated with higher odds of perinatal morbidity, suggesting these guidelines are applicable to a diabetic population.
Obesity is a growing epidemic in the United States. In 2007 through 2008, nearly 60% of reproductive-age American women were reported to be overweight or obese, with the prevalence of obesity reported at approximately 30% across many demographic groups. Prepregnancy obesity is a risk factor for adverse maternal and neonatal outcomes, including spontaneous abortion, gestational diabetes mellitus (GDM), cesarean delivery, preeclampsia, neonatal macrosomia, and operative and anesthetic complications.
The Institute of Medicine (IOM) first established guidelines for weight gain during pregnancy in 1990. These guidelines, with weight based on Metropolitan Life Insurance tables, were based primarily on neonatal outcomes. In the 2 decades since these original guidelines were published, the American population has become considerably more obese. In 2009 the IOM published new guidelines for recommended gestational weight gain that take into consideration maternal morbidity ( Table 1 ). The revised guidelines categorize recommended weight gain based on the World Health Organization (WHO) body mass index (BMI) categories. They include more specific, narrower ranges of recommended weight gain for obese women, rather than an open-ended recommendation. It has been demonstrated that extremely low or high gestational weight gain is associated with adverse perinatal outcomes across all weight groups. Low gestational weight gain has been associated with increased likelihood of small-for-gestational-age (SGA) neonates and of preterm birth, whereas excessive gestational weight gain has been associated with multiple types of neonatal morbidity and mortality, including neonatal macrosomia, and increased cesarean delivery and maternal morbidity.
| Prepregnancy BMI | BMI, kg/m 2 | Total weight gain range, lb | Rates of weight gain, second and third trimesters, lb/wk (mean range) |
|---|---|---|---|
| Underweight | <18.5 | 28–40 | 1 (1–1.3) |
| Normal weight | 18.5–24.9 | 25–35 | 1 (0.8–1) |
| Overweight | 25.0–29.9 | 15–25 | 0.6 (0.5–0.7) |
| Obese | ≥30.0 | 11–20 | 0.5 (0.4–0.6) |
Currently, the IOM recommendations on gestational weight gain are based on prepregnancy BMI and do not take into consideration different race/ethnicity, age, or preexisting medical conditions. Women with type 2 diabetes mellitus (T2DM) are already at increased risk of cesarean delivery, preeclampsia, congenital anomalies, neonatal macrosomia, intrauterine fetal demise (IUFD), multiple other neonatal morbidities, and exacerbation of diabetic end-organ damage. As obesity and T2DM are frequently comorbid conditions, obesity and excessive gestational weight gain may compound these risks in diabetic women. Because fat is an endocrine organ and interacts with diabetes, it is possible that the increased accumulation of fat has a differential effect on perinatal outcomes for women with T2DM. Ample diabetes literature, including data from the large-scale Nurses’ Health Study, suggest that excess body weight aggravates insulin resistance (in nonpregnant patients), and that even modest changes in body weight can impact the development of diabetes as well as diabetes outcomes. It is possible that this principle applies to gestational weight gain and perinatal outcomes as well. Previous data have established that excessive gestational weight gain among women with GDM is associated with increased neonatal morbidity. However, the effect of gestational weight gain in a population of women with T2DM has not yet been studied, and it is unclear whether the latest 2009 IOM guidelines for pregnancy weight gain are applicable to a T2DM population, given the possible compound effect of obesity and diabetes.
Given this background, we designed a retrospective cohort study to examine whether these narrower pregnancy weight gain recommendations are predictive of adverse perinatal outcomes in a population of women with known T2DM. Our objective was to examine if the revised 2009 IOM guidelines for pregnancy weight gain apply to and are predictive of adverse perinatal outcomes in women with T2DM. We hypothesized that the new guidelines would be applicable to this population of overweight and obese women with T2DM. Furthermore, we hypothesized that, as in a population of women with GDM, weight gain beyond the IOM recommendations would be predictive of adverse perinatal outcomes.
Materials and Methods
We conducted a retrospective cohort study of all women with T2DM who were cared for in the Sweet Success California Diabetes and Pregnancy Program (CDAPP) from 2001 through 2004. In California, Sweet Success is the clinical component of CDAPP, which provides technical support and education to providers involved in the care of high-risk pregnant women with preexisting diabetes and women who develop GDM. As a part of the Maternal, Child, and Adolescent Health Branch of the California Department of Health Services, CDAPP collects data on all women enrolled in Sweet Success, including hemoglobin A1c, weight at enrollment and last visit, maternal outcomes, neonatal outcomes, treatments instituted, and demographic information. CDAPP oversees collection by trained clinicians into standardized data collection forms. Institutional review board approval was obtained from the University of California, San Francisco, Committee on Human Research for this study.
The study population includes all overweight and obese women with T2DM who were enrolled in the CDAPP during the years under investigation. Exclusion criteria included: GDM, type 1 diabetes mellitus, multifetal gestations, and pregnancies with fetal anomalies. Overweight and obese women were specifically chosen because the changes to the IOM recommendations in 2009 focused on these groups and they are at highest risk for morbidity. All data were collected from the CDAPP/Sweet Success data collection forms. Prepregnancy weight was classified using the WHO guidelines for calculation of BMI. Women classified as having pre-GDM were those with known preexisting T2DM prior to conception, with a hemoglobin A1c >6.5% in the first trimester, or with a diagnosis of GDM made <14 weeks’ gestational age. Once identified, these women were classified by gestational weight change. Change in pregnancy weight was calculated as the difference between prepregnancy weight and weight at the last reported clinic visit. Using the 2009 IOM guidelines, weight change was then categorized as weight loss (<0 lb), weight gain less than IOM guidelines according to maternal prepregnancy BMI, weight gain within IOM guidelines, and weight gain beyond IOM guidelines. For this study, we focus on gestational weight gain.
Further, since women who delivered preterm or experienced IUFD preterm might have a shorter gestational length to gain weight, we additionally examined the association of gestational weight gain and these outcomes by calculating expected gestational weight gain per week based on the IOM guidelines: between 15-25 lb divided by 38 weeks for overweight and 11-20 lb divided by 38 weeks for obese women. We used 38 weeks’ gestational length as we assume normal pregnancy to be 40 weeks in length, but not accounting for the 2 weeks between last menstrual period to ovulation when the woman is actually not pregnant. After determining expected gestational weight gain per week based on IOM guidelines, we then determined the actual gestational weight gain per week (again, using 38 weeks as the denominator) and categorized women to having gestational weight gain per week below, within, or above IOM recommendations.
Deliveries were performed at a variety of academic and community institutions throughout California, with all data reported by CDAPP clinic providers to the centralized CDAPP database. Neonatal outcomes of interest in this study included: preterm delivery <37 weeks, elevated birthweight (>4000 g), large-for-gestational-age status (>90th centile by gestational age), SGA status (<10th centile by gestational age), neonatal intensive care unit (NICU) admission, and IUFD. Neonatal outcomes were controlled for gestational age at delivery. CDAPP does not collect data on neonatal hypoglycemia or jaundice. Maternal outcomes include all and primary cesarean deliveries; CDAPP does not collect data on preeclampsia. Categorical perinatal outcomes were examined by category of gestational weight change using Pearson χ 2 statistic for analysis of trend. A P value of < .05 indicated statistical significance. Multivariable logistic regression analysis was utilized to control for potential confounders, including age, race/ethnicity, parity, and maternal education.
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