751: The risk of stillbirth at term and timing of delivery in obese women

Abstract

The proportion of obesity in women of reproductive age has been increasing throughout the years. Previous studies have shown that a high body mass index (BMI) is an independent risk factor for stillbirth. The purpose of this study was to determine if obese women should receive early induction of labour to decrease the risk of stillbirth in this population. We conducted a retrospective population-based cohort study using the United States’ Center for Disease Control and Prevention’s Period Linked Birth-Infant Death and Fetal Death data. The study population included all singleton, term or post-term births with a recorded pre-pregnancy BMI that occurred between 2014 and 2017, inclusively. The rate of stillbirths in each BMI class was calculated at each gestational week from 37 weeks and onwards. Of the total of 12,750,751 births in our cohort that met study criteria, 46.77% were to women with a normal weight (BMI=18.5-24.9 kg/m2), 26.94% were to women who were classified as overweight (BMI = 25-29.9 kg/m2), 14.52% were to women in obesity class I (BMI = 30.0-34.9 kg/m2), 6.96% in obesity class II (BMI = 35.0-39.9 kg/m2) and 4.82% in obesity class III (BMI ≥40.0 kg/m2). There were 15,162 cases of term stillbirths over the period of 4 years, for an overall rate of 11.89/10,000 births. Rates of stillbirth appeared to be relatively constant over the study period. As compared to women with a normal BMI, there was a higher rate of stillbirth at each gestational age from 37 weeks among women who were overweight and obese with a dose dependant relationship with respect to BMI. In particular, among morbidly obese women with a BMI of ≥40.0 kg/m2, there was a significant increase in the rate of stillbirth between 39 and 40 weeks. As of 37 weeks of gestation, the rates of stillbirths among women with a high BMI, particularly above 40kg/m2, is considerably greater than for women with a normal BMI. Consideration should be given to early induction among these women as of 37 weeks to reduce the increased risk of stillbirth.