Effect of Excess Gestational Weight Gain on Pregnancy Outcomes in Women With Type 1 Diabetes

Scifres, Christina M. MD; Feghali, Maisa N. MD; Althouse, Andrew D. PhD; Caritis, Steve N. MD; Catov, Janet M. PhD

Obstetrics & Gynecology:
doi: 10.1097/AOG.0000000000000271
Contents: Original Research
Abstract

OBJECTIVE: To evaluate the prevalence and clinical effects of excess gestational weight gain on birth weight and other pregnancy outcomes in women with type 1 diabetes.

METHODS: We performed a retrospective cohort study of women with type 1 diabetes delivered between 2009 and 2012. Patients with excess weight gain were identified using the 2009 Institute of Medicine weight gain recommendations adjusted for gestational age at delivery and prepregnancy body mass index (BMI) category. Demographic and outcome data were abstracted from the medical record, and pregnancy outcomes were compared between women with and without excess gestational weight gain.

RESULTS: Excess gestational weight gain occurred in 114 of 175 women (65.1%). Large-for-gestational-age (LGA) birth weight occurred in 48 of 114 (42.1%) of women with excess gestational weight gain and 5 of 61 (8.2%) of women with recommended weight gain (P<.001). The association between excess maternal weight gain and LGA birth weight remained significant after adjustment for prepregnancy BMI, gestational age at delivery, nulliparity, vascular complications, and hemoglobin A1c measurements (adjusted odds ratio 8.9, 95% confidence interval 3.1–26.2, P<.001). Stratified analyses demonstrated that excess maternal weight gain is associated with LGA neonates in both normal-weight and overweight or obese women.

CONCLUSIONS: Excess maternal weight gain is common and leads to higher rates of LGA neonates in both normal-weight and overweight or obese women with type 1 diabetes. Interventions designed to limit excess gestational weight gain may reduce the risk for fetal overgrowth in women with type 1 diabetes.

LEVEL OF EVIDENCE: II

In Brief

Excess maternal weight gain is common and leads to higher rates of large-for-gestational-age neonates in both normal-weight and obese women with type 1 diabetes.

Author Information

Department of Obstetrics, Gynecology and Reproductive Sciences, Magee Women’s Research Institute, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania.

Corresponding author: Christina M. Scifres, MD, 300 Halket Street, Pittsburgh, PA 15213; e-mail: scifresc@mail.magee.edu.

Presented at the Society for Maternal-Fetal Medicine Annual Meeting, February 3–8, 2014, New Orleans, Louisiana.

Financial Disclosure The authors did not report any potential conflicts of interest.

Article Outline

The prevalence of obesity is increasing in nonpregnant patients with type 1 diabetes.1,2 However, most studies examining pregnancy outcomes in women with type 1 diabetes were conducted in countries with low obesity rates3 or before the onset of the obesity epidemic.4 Weight gain is a common problem in nonpregnant patients with type 1 diabetes using intensive insulin regimens,5 but the prevalence of excess gestational weight gain in pregnant women with type 1 diabetes is unknown.

In 2009 the Institute of Medicine issued revised guidelines for recommended gestational weight gain based on the World Health Organization body mass index (BMI, calculated as weight (kg)/[height (m)]2) categories.6 Excess weight gain is known to aggravate insulin resistance and affect diabetes outcomes in nonpregnant individuals with type 1 diabetes.1 However, the effect of excess weight gain on glycemic control and pregnancy outcomes in women with type 1 diabetes is unknown.

Women with type 1 diabetes are at significant risk for pregnancy complications including large-for-gestational-age (LGA) birth weight.3,7,8 Rates of macrosomia remain high despite hemoglobin (Hb)A1c levels close to the normal range,9,10 demonstrating that factors other than maternal glucose control contribute to the excess morbidity seen in pregnant women with type 1 diabetes.

Therefore, we designed this study to examine the prevalence of excess gestational weight gain and to evaluate the effect of maternal weight gain on common pregnancy complications such as LGA birth weight in women with type 1 diabetes. We hypothesized that weight gain in excess of the Institute of Medicine recommendations would be predictive of LGA birth weight.

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MATERIALS AND METHODS

We conducted a retrospective cohort study of all women with type 1 diabetes and singleton pregnancies who were delivered at Magee-Womens Hospital (University of Pittsburgh, Pittsburgh, Pennsylvania) from January 2009 to October 2012. Women were identified using the International Classification of Diseases, 9th Revision, Clinical Modification codes 648.01 (diabetes-delivered) and 648.81 (abnormal glucose tolerance-delivered). We identified 2,339 women with diabetes delivered over the study period, and charts were reviewed to identify 176 women with type 1 diabetes based on clinical history (7.5% of women with diabetes at delivery). Information on pregnancy weight gain was available for 175 women who were included in the final analysis (one patient presented in labor and delivered at 35 weeks of gestation with no prenatal care). Women received prenatal care in the maternal-fetal medicine office and obstetrics clinics at our hospital, and they were seen by dedicated diabetes dieticians who provided consultation regarding their diet and recommended weight gain based on their prepregnancy BMI. Self-monitoring of plasma glucose was recommended seven times daily, and targets for plasma glucose included a fasting value less than 95 mg/dL (5.3 mmol/L) and 1-hour postmeal values less than 140 mg/dL (7.8 mmol/L). Women had a serum creatinine and either a urinary protein-to-creatinine ratio or 24-hour urine collection performed to assess baseline renal function. Demographic and clinical data on the mother and newborn were obtained from the original medical record. Regulatory approval was obtained from the University of Pittsburgh institutional review board, and informed consent was not required given the retrospective nature of the study.

The primary exposure of interest in our study was gestational weight gain, which was calculated as the difference between self-reported weight before pregnancy and the last weight recorded before delivery. For 67 of 175 (38%) of women we were able to verify the self-reported prepregnancy weight by review of the patient's medical records for the 6 months before conception. We found that self-reported maternal prepregnancy weight correlated strongly with both documented pregravid weight (r=0.99, P<.001) and measured weight at the first prenatal visit (r=0.97, P<.001) so we elected to use the maternal self-reported prepregnancy weight for our analyses. Excessive gestational weight gain was defined as gestational weight gain greater than the upper range of Institute of Medicine 2009 guidelines for each prepregnancy BMI category (underweight, normal weight, overweight, and obese) for women who delivered beyond 37 weeks of gestation6 (Table 1). Because many women (n=70/175 [40%]) delivered preterm, we additionally examined the association of excess gestational weight gain and outcomes in patients delivered preterm by estimating the maximal gestational weight gain at the gestational age at which they were delivered. We performed these calculations by multiplying the maximal weekly weight gain in the second and third trimesters times the number of weeks preterm the patient was delivered and subtracting this value from the maximum recommended weight gain for each BMI category. Maternal prepregnancy overweight and obesity was reported as an index of weight for height (BMI) and overweight or obesity was defined using the World Health Organization guidelines for classification of BMI. Only 3 of 175 women (1.6%) of women had a prepregnancy BMI that was considered underweight, so these women were included with the normal-weight women for purposes of this analysis. In addition, only 7 of 175 women (4.0%) had a weight gain that was less than expected based on the Institute of Medicine recommendations, so they were grouped with the recommended weight gain group. Sensitivity analyses were undertaken excluding women with an underweight BMI and suboptimal weight gain, and the overall findings of the study were unchanged so they remained in final analysis.

Maternal demographics and clinical characteristics were extracted from the chart. Diabetic nephropathy was defined as greater than 0.3 g protein on 24-hour urine collection and retinopathy assessed by patient report and review of ophthalmology records. Hemoglobin A1c values were recorded by the trimester in which they were measured. When more than one measurement per trimester was available the values were averaged, and the mean HbA1c across pregnancy was also calculated. We also abstracted the type of therapy used in each trimester and at delivery, and these were grouped based on the basal insulin therapy including either neutral protamine Hagedorn insulin, insulin glargine, or insulin pump therapy. Chronic hypertension was defined as blood pressure 140/90 mmHg or greater diagnosed before pregnancy before 20 weeks of gestation.

Pregnancy outcomes were compared between women with standard and excess gestational weight gain including gestational age at delivery, preterm delivery less than 37 weeks of gestation, LGA (greater than the 90th percentile for gestational age) or small for gestational age (less than the 10th percentile for gestational age) status based on U.S. national birth weight data,11 macrosomia (defined as a birth weight greater than 4,000 g), ponderal index, placental weight, cesarean delivery, shoulder dystocia, and stillbirth. Gestational hypertension was defined as new-onset resting blood pressure greater than 140/90 mmHg on two or more occasions 6 hours apart in the second half of pregnancy with absence of significant proteinuria. Mild preeclampsia was defined as a systolic blood pressure of 140 mmHg or greater or a diastolic blood pressure of 90 mmHg or greater on two occasions at least 6 hours apart occurring after 20 weeks of gestation accompanied by detectable urinary protein (1+ or greater by dipstick or 0.3 g or greater/24 hours). Severe preeclampsia was defined as a blood pressure 160/110 mmHg or greater with either a urine dipstick demonstrating 3+ or 4+ protein in a random urine sample or greater than 5.0 g of proteinuria over 24 hours. Other criteria for severe disease included eclampsia, pulmonary edema, oliguria (less than 500 mL/24 hours), fetal growth restriction, oligohydramnios, and symptoms suggestive of significant end-organ involvement (headache, visual disturbance, or epigastric or right upper quadrant pain). Superimposed preeclampsia was diagnosed in the setting of blood pressure exacerbations along with new-onset proteinuria (0.3 g or greater/24 hours). Neonatal outcomes included neonatal intensive care unit admission, hypoglycemia (defined as a glucose value less than 35 mg/dL within the first 24 hours of life), hyperbilirubinemia requiring phototherapy, respiratory distress syndrome, congenital anomalies, and neonatal death.

Statistical analyses were completed using Stata 10 Special Edition and SAS 9.4. Distributions of variables were tested for normality using visual inspection of histograms and the Shapiro–Wilk W-test. Women with and without excess gestational weight gain were compared using χ2 statistic, Fisher’s exact test, or t tests as appropriate. Effect modification by prepregnancy BMI (as a continuous variable) was assessed using the likelihood ratio test. Multivariable logistic regression analysis was used to analyze whether excess gestational gain was associated with the aforementioned pregnancy outcomes when controlling for potential confounders, including age, parity, maternal education, glycemic control, the presence of vascular complications, and prepregnancy BMI. Repeated-measures analysis was undertaken to examine differences in gestational weight gain per trimester between women who delivered LGA neonates compared with those that delivered appropriate-for-gestational-age neonates; this was performed only in the 137 women who had complete data on weight gain in each trimester in addition to prepregnancy and delivery weight. Mean weights in each group were plotted for each trimester, and an interaction between LGA delivery and trimester was tested to determine whether there was a difference in the pattern of weight gain across trimesters between women that delivered LGA neonates compared with those who delivered appropriate-for-gestational-age neonates. P values <.05 were considered significant in all analyses.

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RESULTS

The mean weight gain was 34.1±14.1 pounds (range 0–83 pounds) for the entire cohort. Excess weight gain was a common occurrence, affecting 114 of 175 (65.1%) of the overall cohort. Notably, women with excess gestational weight gain gained significantly more than the upper limits of recommended weight gain (14.8±10.7 pounds). Table 2 shows the clinical characteristics of women with appropriate compared with excess gestational weight gain. As expected, women in the excess gestational weight gain group gained almost twice as much weight as those women in the appropriate weight gain group. Women with excess gestational weight gain were more likely to be overweight or obese before pregnancy, and they were also more likely to have at least some college education. Women with standard weight gain were more likely have vascular complications (either retinopathy or nephropathy). In the overall cohort the mean HbA1c values decreased from the first trimester to the third trimester (7.8±1.8% compared with 6.7±1.1%, P<.01). Women with excess maternal weight gain demonstrated lower mean HbA1c values in the first trimester, although by the third trimester, mean HbA1c values were similar between groups (Table 2).

Gestational age at delivery and rates of preterm delivery were similar between women with excess gestational weight gain and those without. However, women with excess gestational weight gain had larger mean birth weights, placental weights, and their neonates had higher ponderal indices. They also experienced much higher rates of LGA birth weight and macrosomia, whereas rates of small-for-gestational-age birth weight were similar between groups (Table 3).

There were no significant interactions between prepregnancy BMI and gestational weight gain with regard to LGA birth weight. We performed a stratified analysis to assess the magnitude of the effect of excess weight gain on LGA birth weight separately in normal-weight and overweight or obese women. Excess weight gain was associated with LGA birth weight in both normal-weight (15/22 [40.5%] compared with 2 of 31 [6.5%], P=.001, odds ratio [OR] 9.9, 95% confidence interval [CI] 1.9–95.0) and overweight or obese women (33/77 [42.9] compared with 3 of 30 [10%], P=.001, OR 6.8, 95% CI 1.8–37.1, Mantel-Haenszel test for homogeneity P<.01). We next performed a multivariable logistic regression analysis to further characterize the relationship between excess maternal weight gain and LGA birth weight. Excess maternal weight gain remained independently associated with LGA birth weight after adjustment for prepregnancy BMI, vascular complications, mean HbA1c across gestation, gestational age at delivery, nulliparity, and maternal education (48/114 [42.1%] compared with 5 of 61 [8.2%], P<.001, adjusted OR 8.9, 95% CI 3.1–26.2, P<.001) (Table 4). The risk of having an LGA neonate was the same in women who achieved a mean HbA1c value 6.5% or less and those who had a mean HbA1c value greater than 6.5% (30.1 compared with 30.7%, P=.94), and the type of treatment used did not alter the risk for having an LGA neonate. Because of the possibility that pregnancy complications leading to preterm birth could also affect risk for LGA birth weight, we performed a sensitivity analysis including only the 126 women who delivered at or beyond 36 0/7 weeks of gestation. We found that excess maternal weight gain was associated with LGA birth weight in women who were delivered at or near term (42/83 [50.6%] compared with 5/43 [11.6%], P<.001, OR 7.8, 95% CI 2.8–21.7, P<.001), similar to our findings in the overall cohort. We also noted the strong relationship between vascular complications and LGA birth weight. We therefore analyzed the association between gestational weight gain and LGA birth weight after excluding the 31 women with vascular complications and found that excess gestational weight gain remained significantly associated with LGA birth weight (47/100 [47%] compared with 5/44 [11.4%], P<.001, OR 6.9, 95% CI 2.5–19.0, P<.001).

We then proceeded to examined weight gain patterns during each trimester for women with appropriate-for-gestational-age and LGA neonates in the 137 women with a recorded weight at all four time points. Women that delivered LGA neonates were moderately heavier prepregnancy (P=.06) and significantly heavier at the first trimester, second trimester, and delivery (P<.05 for all; Fig. 1). Women who delivered LGA neonates had significantly greater first-trimester weight gain than those who delivered appropriate-for-gestational-age neonates (8.2 pounds compared with 5.3 pounds, P=.01), similar second-trimester weight gain (14.6 pounds compared with 12.9 pounds, P=.11), and significantly greater third-trimester weight gain (16.8 pounds compared with 12.7 pounds, P=.002). There was a statistically significant interaction between delivery of an LGA neonate and time (P=.01), indicating that women who ultimately delivered LGA neonates were not only heavier at study entry but that they also gained more weight than their counterparts who delivered appropriate-for-gestational-age neonates.

As a result of the modest sample size, we lacked statistical power to compare infrequent outcomes between those with expected and excess gestational weight gain, but there was a trend toward higher rates of cesarean delivery in women with excess gestational weight gain. However, this relationship was not significant after adjustment for LGA birth weight, gestational age at delivery, overweight or obese status, and pregnancy-induced hypertension (78/114 [68.4%] compared with 33/61 [54.1%], P=.06, adjusted OR 1.3, 95% CI 0.6–2.6, P=.34). Shoulder dystocia rates were similar between groups. There were two stillbirths in the study participants, both complicated by multiple fetal anomalies (Table 3) Neonatal outcomes were similar between women with expected and excessive maternal weight gain, and there were no other significant relationships between excess gestational weight gain and other pregnancy outcomes.

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DISCUSSION

Excess gestational weight gain is a common occurrence in women with type 1 diabetes. This excess gestational weight gain leads to increased risk for LGA birth weight and macrosomia as well as higher ponderal indices, suggesting that the observed increase in birth weight may result from increased aiposity. The association between excess gestational weight gain and LGA birth weight was robust in both normal-weight and overweight or obese women Notably, excess weight gain as early as the first trimester results in an increased risk for LGA birth weight. We hypothesize that interventions to limit excess gestational weight gain may need to occur preconception or early in pregnancy to reduce the prevalence of LGA neonates. Macrosomic neonates of diabetic mothers have higher body fat compared with nondiabetic control neonates of similar weight and length,12 and this increased adiposity may predispose to obesity, diabetes, and cardiovascular disease later in life.13–16 Therefore, effective strategies to reduce the risk for LGA birth weight may have beneficial long-term effects on the offspring of women with type 1 diabetes.

Our findings are consistent with prior studies, which have shown that excess gestational weight gain is associated with an increased risk for LGA birth weight in women with gestational diabetes17 or type 2 diabetes.18 However, the mechanisms linking excess gestational weight gain to LGA birth weight are incompletely understood. Increased body fat in patients with type 2 diabetes is associated with higher levels of proinflammatory adipocytokines, ectopic fat stores, dyslipidemia, insulin resistance, oxidative stress, and hypofibrinolysis or procoagulation,1 but additional studies are needed to understand the physiologic adaptations in pregnancies complicated by type 1 diabetes and obesity or excess gestational weight gain. Hypertriglyceridemia is an established risk factor for LGA birth weight in pregnancies complicated by gestational diabetes,19 but the effect of dyslipidemia on fetal growth in pregnancies with type 1 diabetes is unknown. There are some similarities in placental gene expression relating to fatty acid transport and activation between women with gestational diabetes and type 1 diabetes,20 suggesting that there may be common pathways to fetal overgrowth in pregnancies complicated by type 1 diabetes and other forms of diabetes.

Pregnant women are counseled regarding the importance of good glycemic control, and the observed reduction in HbA1c levels across gestation suggests that this counseling was effective. More troubling is that rates of LGA were similar between women who achieved a mean HbA1c less than 6.5% and those who did not, indicating that mechanisms other than suboptimal glucose control contribute to fetal overgrowth in women with type 1 diabetes. Weight gain is a common problem with intensive insulin regimens, and this weight gain has significant metabolic effects outside of pregnancy including elevations in serum lipids, blood pressure, and abdominal obesity.5,21 This constellation of lipid abnormalities, abdominal obesity, and hypertension is similar to the central obesity–insulin resistance syndrome that is characteristic of type 2 diabetes and highlights the possibility of metabolic deterioration associated with excess weight gain in pregnant patients with type 1 diabetes. Gestational weight gain also has long-term effects on women with type 1 diabetes. Cyganek et al22 observed that women with type 1 diabetes who experienced a pregnancy weighed 2.5 kg more than their prepregnancy baseline after a median of 20 months postpartum. This long-term weight retention may have significant effects on both glycemic control and risk for cardiovascular disease, particularly for women affected by both obesity and type 1 diabetes.

The retrospective nature of this cohort study and the relatively modest sample size lacked statistical power to adequately examine the association between excess gestational weight gain and rare outcomes such as shoulder dystocia or birth trauma. Our cohort included a small number of patients with underweight BMI or inadequate weight gain, so we were unable to assess the relationship between these factors and adverse pregnancy outcomes. Women in our study were mostly white and there were few women with significant vascular disease; therefore, our results may not be generalizable to all pregnancies complicated by type 1 diabetes.

Maintaining maternal weight gain within the Institute of Medicine guidelines based on prepregnancy BMI may reduce the risk of LGA birth weight in women with type 1 diabetes. Although there are few data demonstrating how to manage weight gain in this population, intensive patient education regarding weight gain goals may be most effective if it starts preconceptionally and continues early in gestation with regular reinforcement throughout pregnancy.23,24 Future studies into the metabolic adaptations associated with excess weight gain will also identify the optimal dietary and medical targets to reduce the risk for fetal overgrowth, which may have long-term benefits for women with type 1 diabetes and their offspring.

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