Association Between Prepregnancy Body Mass Index and Severe Maternal Morbidity

Several studies have shown that overweight and obesity are associated with adverse neonatal outcomes including preterm birth, severe congenital anomalies, and infant death. While some studies show an association between maternal obesity and pregnancy complications such as preeclampsia, thromboembolism, and cesarean delivery, less is known about the association between body mass index (BMI) and life-threatening maternal morbidity. This retrospective cohort study aimed to analyze the association between prepregnancy BMI and severe maternal morbidity (SMM). Information on all singleton births in Washington State was collected between 2004 and 2013 and included maternal and infant characteristics and labor course. The primary outcome measured was SMM or mortality, defined as a composite outcome of life-threatening conditions, conditions leading to serious sequelae, complications leading to intensive care unit admission, and maternal death during hospitalization for childbirth. Statistical tools included sensitivity analyses for confounder adjustment, and logistic regression analyses were used to determine adjusted odds ratios (aORs) and 95% confidence intervals (CIs) for the association between maternal morbidity or mortality and BMI. Obesity was separated into 3 classes by BMI: class 1 (30.0-34.9 kg/m(2)), class 2 (35.0-39.9 kg/m(2)), and class 3 (>= 40.0 kg/m(2)). A total of 743,660 women were deemed eligible and included in the study group. Underweight women (3.2%) and those with normal BMI (47.5%) included a high proportion of Hispanic and nulliparous women. Obese women (13.1% class 1, 6.2% class 2, 4.2% class 3) had a higher rate of preexisting diabetes, chronic hypertension, cesarean and previous cesarean delivery, prior infant death, small for gestational age, labor induction, hypertension in pregnancy, and gestational diabetes. Women with normal BMI had the lowest rate of SMM or mortality (143.2 per 10,000), whereas women with class 3 obesity had the highest rate (202.9 per 10,000). Compared with the normal BMI sample, rates of SMM were significantly higher among underweight (OR, 1.2; 95% CI, 1.0-1.3), overweight (OR, 1.1; 95% CI, 1.1-1.2), and obese women (for women with class 1 obesity: OR, 1.1 [95% CI, 1.1-1.2]; for women with class 2 obesity: OR, 1.2 [95% CI, 1.1-1.3]; and for women with class 3 obesity: OR, 1.4 [95% CI, 1.3-1.5]). Adjusting for higher-than and lower-than-recommended amount of weight gain during pregnancy did not significantly change the associations between BMI and SMM or mortality. The study shows that, at least among pregnant women in Washington State, a low or high BMI compared with a normal prepregnancy BMI is significantly associated with a higher rate of SMM or mortality. Rates of SMM and mortality showed a dose-response pattern among women with above normal prepregnancy BMI.