Timing of delivery in obese women and risk of stillbirth

Increased body mass index (BMI) is an independent risk factor for stillbirth. The purpose of this study was to determine an optimal time of delivery at term in obese women in order to decrease the risk of stillbirth in this population.

We conducted a retrospective population-based cohort study using the CDC's Period Linked Birth-Infant Death and Fetal Death data. The study population included all singleton, term births with a recorded pre-pregnancy BMI that occurred between 2014 and 2017. Unconditional logistic regression analyses were used to estimate the risk of stillbirth in each BMI class at each gestational week from 37 weeks and onwards comparing with births to normal-weight women at 41 weeks.

Of 12,742,980 births in our cohort, 46.8% were to women with a normal BMI, 26.9% were to women who were classified as overweight, 14.5% were to women in obesity class I, 7.3% in obesity class II, and 4.8% in obesity class III. Within each BMI class, the risk of stillbirth increased with gestational age, with the most pronounced rises in risk occurring at later gestational ages. In a dose-response relationship, the risk of stillbirth exceeded that of a normal BMI pregnancy at 41 weeks at the following gestational age and BMI category: obese class 1 at 39 weeks (OR 1.15 95% CI 1.00-1.31), obese class II at 38 weeks (OR 1.21 95% CI 1.04-1.41) and obese class III at 37 weeks (OR 1.30 95% CI 1.11-1.52).

Compared to women with a normal BMI at 41 weeks, there was a higher risk of stillbirth at term in women with each increase in BMI class. Consideration should be given to early induction among these women to reduce the risk of stillbirth.