Objective
The Institute of Medicine (IOM) does not provide recommendations for gestational weight gain (GWG) specific to women with pregestational diabetes. We aimed to assess the impact of GWG outside the IOM recommendations on perinatal outcomes.
Study Design
We performed a retrospective cohort study of all singletons with pregestational diabetes from 2008 through 2013. Women were classified as GWG within, less than, or greater than IOM recommendations for body mass index per week of pregnancy. Maternal outcomes examined were cesarean delivery, preeclampsia, and percentage of visits with glycemic control (>50% blood sugars at goal). Neonatal outcomes were birthweight, small for gestational age (<10th percentile), large for gestational age (LGA) (>90th percentile), macrosomia (>4000 g), preterm delivery (<37 weeks), and birth injury (shoulder dystocia, fracture, brachial plexus injury, cephalohematoma). Groups were compared using analysis of variance and χ 2 test, as appropriate. Backwards stepwise logistic regression was used to adjust for confounding factors.
Results
Of 340 subjects, 37 (10.9%) were within, 64 (18.8%) less than, and 239 (70.3%) greater than IOM recommendations. The incidence of cesarean delivery, preeclampsia, glycemic control, preterm delivery, and birth injury were not significantly different between GWG groups. The incidence of LGA and macrosomia increased as GWG category increased (adjusted odds ratio [AOR], 3.08; 95% confidence interval [CI], 1.13–8.39 and AOR, 4.02; 95% CI, 1.16–13.9, respectively) without decreasing the incidence of small for gestational age (AOR, 0.34; 95% CI, 0.10–1.19). Increases in the risk in LGA and macrosomia were not explained by differences in glycemic control by GWG groups.
Conclusion
Women with pregestational diabetes mellitus should be counseled to gain within the IOM recommendations to avoid LGA and macrosomic newborns.
Pregestational diabetes complicates 1% of all pregnancies in the United States. The number of pregnancies complicated by diabetes is increasing ; the age-adjusted rate of pregestational diabetes doubled from 1996 through 2010. Furthermore, currently one half of pregnant women are overweight or obese and obesity increases the lifetime risk of diabetes by as much as 74% for women.
Pregestational diabetes increases the risk for preeclampsia, primary cesarean, fetal anomalies, macrosomia, preterm delivery (PTD), stillbirth, and growth restriction. Maternal glycemic control can reduce the risk of these complications. Given the association among obesity, weight gain, and insulin resistance, gestational weight gain (GWG) in this population may contribute to adverse maternal and neonatal outcomes.
The Institute of Medicine (IOM) has developed guidelines for GWG to target an ideal birthweight. However, these guidelines were developed in a healthy population and no specific guidelines were created for special populations such as pregestational diabetics. GWG is directly linked to birthweight, which is in turn linked to mode of delivery and neonatal outcomes. Therefore, it is essential to evaluate these guidelines as this patient population continues to expand.
Consequently, we aimed to evaluate the effect of GWG in pregestational diabetics outside the IOM guidelines on perinatal outcomes. We predicted a high proportion of women will gain more than IOM recommendations and that these women will have more large-for-gestational-age (LGA) neonates with a higher risk of cesarean delivery, preeclampsia, PTD, and birth injury.
Materials and Methods
This was a retrospective cohort study of all singleton pregnancies at a tertiary care center complicated by pregestational diabetes from 2008 through 2013. The study period was determined by the years when the complete electronic medical record was available for reliable data collection. Institutional review board approval was obtained from the University of Alabama at Birmingham.
Subjects were identified by a diagnosis of pregestational diabetes in our searchable electronic medical records. Subjects who reported a diagnosis of diabetes prior to pregnancy were considered to have pregestational diabetes; women diagnosed with diabetes at any point during pregnancy (even at early gestational ages) were not included in this study. Trained chart abstractors completed standardized chart abstraction forms and the principal investigator reviewed >3% of all abstracted charts. Data collected included maternal demographics, medical and obstetrical history, diabetes diagnosis and care, prenatal blood sugar logs, medication use, labor and delivery events, and neonatal outcomes. Chart abstractors reviewed each patient’s blood sugar logs for each visit and determined the number of values recorded, the number of values above goal for each visit, and the number of blood sugars <60 mg/dL. All women were managed under the supervision of maternal-fetal medicine specialists. Per institutional protocol, patients met with a nutritional counselor and diabetic educator at their initial visit and as needed throughout their pregnancy. Also per institutional protocol, patients were seen every 1-2 weeks and adjustments were made to insulin regimen when either >50% of the fasting or 50% of the postprandial blood sugars were elevated. Patients with <3 fasting or 7 postprandial blood sugars recorded were assumed to have poor control. Subjects were excluded for incomplete body mass index (BMI) data, last weight measured >14 days before delivery, major maternal comorbidity unrelated to diabetes mellitus (eg, systemic lupus erythematosus, maternal cardiac disease, HIV), late prenatal care (>26 weeks at first prenatal visit), and any fetal anomalies.
GWG per week of the second and third trimesters was calculated as: (last measured weight minus prepregnancy weight) divided by (gestational age at delivery minus 13), assuming a 0.5-2 kg weight gain in the first trimester. Women were classified as GWG within, less than, or greater than the IOM recommendations for prepregnancy BMI. Prepregnancy BMI was determined by patient report of prepregnancy weight, which has been established as a validated method of obtaining biometric data. Per week of pregnancy in second and third trimesters, the IOM recommends underweight women (BMI <18.5 kg/m 2 ) gain 0.44-0.58 kg/wk, normal-weight women (BMI 18.5-24.9 kg/m 2 ) gain 0.35-0.50 kg/wk, overweight women (BMI 25.0-29.9 kg/m 2 ) gain 0.23-0.33 kg/wk, and obese women (BMI ≥30 kg/m 2 ) gain 0.17-0.27 kg/wk.
Maternal outcomes examined were mode of delivery, preeclampsia, and percentage of visits with glycemic control. To assess the impact of GWG on glycemic control, we assessed patient blood sugar logs. For each visit, a patient was considered to have glycemic control if ≥50% of blood sugars were at goal. To account for variations in the number of visits each patient has during pregnancy, we calculated the percentage of visits with glycemic control by dividing the number of visits with glycemic control by the total number of visits. Neonatal outcomes examined were birthweight, small for gestational age (SGA) (<10th percentile on Alexander standard), LGA (>90th percentile on Alexander standard), macrosomia (>4000 g), PTD (<37 weeks), gestational age at delivery, birth injury (defined as shoulder dystocia as documented by the delivery physician; fracture of the clavicle, humerus, or skull; brachial plexus injury; and cephalohematoma), and neonatal length of stay.
A secondary analysis was performed to measure the impact of GWG on the adverse maternal and neonatal outcomes stratified by type of diabetes (type 1 or type 2 diabetes) and by obesity. Type 1 and type 2 diabetics were determined by history in the medical record. Women exclusively treated with oral agents were determined to be type 2 diabetics. If the subjects’ type was never documented, they were labeled as an unknown type and excluded from the secondary analysis.
Normal distribution of continuous variables was tested using the Kolmogorov-Smirnov test and by visually assessing the histograms. The characteristics and outcomes of subjects gaining within, less than, or greater than the IOM recommendations were compared using analysis of variance or Kruskal-Wallis test and χ 2 test for trend, as appropriate. Clinically relevant covariates for initial inclusion in multivariable statistical models were selected using results of the stratified analyses and factors were removed in a backward stepwise fashion based on significant changes in the exposure adjusted odds ratio or significant differences between hierarchical models using likelihood ratio test. Confounding factors considered include age, race, parity, prior mode of delivery, hypertension, and tobacco use. All analyses were completed using Stata SE, version 11.2 (StataCorp, College Station, TX).
Results
Of 597 women identified with pregestational diabetes, 340 were included in the analysis (62 excluded for major medical problems unrelated to diabetes, 51 excluded for congenital malformations, 9 excluded for late prenatal care, 30 missing prepregnancy BMI, and 105 with missing final weight or weight >14 days prior to delivery). Of these 340 women, 37 (10.9%) gained within the IOM recommendations; 64 (18.8%), less than IOM recommendations; and 239 (70.3%), more than the IOM recommendations. Maternal characteristics according to GWG group are shown in Table 1 . Women in each GWG category were similar with regards to maternal age, race, insurance type, chronic hypertension, prior cesarean delivery, parity, White’s classification, and type of medication regimen. Women gaining less than the IOM recommendations had a higher prepregnancy BMI compared to the within and more than IOM recommendations groups ( P = .021) ( Table 1 ).
| Characteristic | Less than IOM Guidelines, n = 64 | Within IOM guidelines, n = 37 | Above IOM guidelines, n = 239 | P value |
|---|---|---|---|---|
| Age, y | 29.8 ± 6.3 | 27.6 ± 6.6 | 29.6 ± 6.1 | .16 |
| Nulliparous | 28 (43.8) | 13 (35.1) | 92 (38.5) | .65 |
| Race | ||||
| White | 14 (21.9) | 10 (27.0) | 81 (33.9) | .26 |
| Black | 47 (73.4) | 26 (70.3) | 133 (55.6) | |
| Hispanic | 3 (4.7) | 1 (2.7) | 20 (8.4) | |
| Government insurance | 43 (67.2) | 25 (67.6) | 162 (67.8) | .88 |
| Smoking | 15 (23.4) | 10 (27.0) | 51 (21.3) | .72 |
| Prior cesarean delivery | 13 (20.3) | 11 (29.7) | 68 (28.5) | .40 |
| cHTN | 29 (45.3) | 11 (29.7) | 96 (40.2) | .30 |
| White classification | ||||
| B | 21 (32.8) | 11 (29.7) | 63 (26.4) | .43 |
| C | 9 (14.1) | 9 (24.3) | 44 (18.4) | |
| D | 31 (48.4) | 12 (32.4) | 107 (44.8) | |
| R, F, RF | 3 (4.7) | 5 (13.5) | 25 (10.5) | |
| Diabetes type | ||||
| 1 | 14 (21.9) | 14 (37.8) | 68 (28.5) | .39 |
| 2 | 48 (75.0) | 22 (59.5) | 167 (69.9) | |
| Unknown | 2 (3.1) | 1 (2.7) | 2 (0.8) | |
| Type 1 diabetes mellitus insulin pump use | 5 (7.8) | 4 (10.8) | 24 (10.0) | .84 |
| Prepregnancy BMI, kg/m 2 | 37.5 ± 9.8 | 33.8 ± 10.4 | 33.9 ± 9.0 | .021 |
| Prepregnancy BMI category | ||||
| Underweight | 1 (1.6) | 0 (0) | 1 (0.4) | .07 |
| Normal | 5 (7.8) | 10 (27.0) | 28 (11.7) | |
| Overweight | 10 (15.6) | 7 (18.9) | 54 (22.6) | |
| Obese | 48 (75.0) | 20 (54.1) | 156 (65.3) | |
| Gestational weight gain, kg | 0.27 ± 5.9 | 7.2 ± 2.0 | 17.74 ± 9.6 | < .01 |
| Oral medication used during pregnancy (with or without insulin) a | 14 (21.9) | 14 (37.8) | 61 (25.5) | .20 |
| Oral medication only (no insulin) a | 7 (11.3) | 5 (13.4) | 18 (7.8) | .39 |
a Oral medications used were either glyburide or metformin, approximately evenly divided.
Mode of delivery and glycemic control were not significantly different between GWG groups ( Table 2 ). The risk of preeclampsia was not significantly different between GWG groups. As GWG category increased, the risks of LGA and macrosomia increased without a concomitant significant decrease in the incidence of SGA. These results remained statistically significant after controlling for chronic hypertension, type 1 vs type 2 diabetes, and prepregnancy BMI ( Table 3 ).
| Variable | Less than IOM guidelines, n = 64 | Within IOM guidelines, n = 37 (reference group) | Above IOM guidelines, n = 239 | P value (trend) |
|---|---|---|---|---|
| Maternal | ||||
| Mode of delivery | ||||
| Spontaneous | 28 (43.8) | 19 (51.4) | 88 (36.8) | |
| Operative vaginal a | 3 (4.7) | 0 | 10 (4.2) | |
| Cesarean | 33 (51.6) | 18 (48.7) | 141 (59.0) | .33 |
| Preeclampsia | 15 (23.4) | 12 (32.4) | 73 (30.5) | .49 |
| Visits with blood sugar controlled, % | 31.8 ± 28.9 | 28.9 ± 26.8 | 29.7 ± 26.7 | .92 |
| Neonatal | ||||
| Birthweight, g | 2787 ± 990 | 3198 ± 734 | 3296 ± 1109 | < .01 |
| SGA | 5 (7.8) | 4 (10.8) | 13 (5.4) | .41 |
| LGA | 5 (7.8) | 6 (16.2) | 72 (30.1) | < .01 |
| Macrosomia | 4 (6.3) | 4 (10.8) | 56 (23.4) | < .01 |
| PTD | 30 (46.9) | 10 (27.0) | 92 (38.5) | .14 |
| Gestational age at delivery, wk | 35.5 ± 4.6 | 37.4 ± 2.2 | 36.4 ± 4.0 | .24 |
| Birth injury b | 7/60 (11.7) | 3/36 (8.3) | 17/222 (7.7) | .61 |
| Neonatal length of stay, d | 9.1 ± 14.5 | 4.9 ± 7.7 | 7.6 ± 12.1 | .27 |
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