The association of obesity with stillbirth

Abstract

Because antepartum testing is recommended at 34 weeks if pre-pregnancy BMI is ≥40 kg/m2 (class III obesity) or at 37 weeks if it is 35≤BMI< 40 kg/m2 (class II obesity), our aim was to determine the rate of stillbirth with maternal obesity at varying strata. This was a retrospective cohort study of patients with optimally dated, non-anomalous singleton pregnancies delivering at a single academic center between 1 Jan 2013 and 30 Apr 2022. BMI at first prenatal visit was used a proxy for pre-pregnancy BMI. Pregnancies complicated by chronic hypertension, gestational or overt diabetes treated with insulin were excluded as were aneuploidy or growth restriction. Antepartum testing was not available to patients without medical or fetal complications, regardless of BMI. In patients with class III obesity who reached 34 weeks gestation, the rate of stillbirth was calculated at 34 0/7-36 6/7, 37 0/7-38 6/7, and >39 weeks. In those with class II obesity who reached 37 weeks, the rate of stillbirth was calculated at 37 0/7-38 6/7 and >39 weeks. Rates of stillbirth were then compared between normal weight cohort (18.5≤BMI< 25) at these gestational age epochs. Cox proportional regression hazard models were used to estimate the risk of stillbirth in relation to BMI. There were 3060 patients with class III obesity, 5049 patients with class II obesity, and 17555 patients with normal BMI examined. Compared with patients with normal BMI, stillbirth rate was significantly increased beyond 39 weeks in class III obesity (P=0.021, hazard ratio 3.67 with 95% CI 1.07 to 12.56), but not prior to this gestational age. No significant increased risk of stillbirth was identified in class II obesity at term. In our population, we found an increased risk of stillbirth in class III obesity beyond 39 weeks. We did not observe an increased risk prior to this gestational age in class III obesity nor significant risk at term in those with class II obesity. Our findings warrant further investigation into the necessity of antepartum testing in patients with class II and III obesity.