The risk of perinatal mortality with each week of expectant management in obese pregnancies

Introduction: The risk of stillbirth associated with maternal obesity increases with gestational age; however, it is unclear if earlier delivery reduces the overall perinatal mortality rate. Our objective was to compare the risk of perinatal mortality associated with each additional week of expectant management to that of immediate delivery.

Methods: This was a retrospective cohort study of singleton non-anomalous births in Texas between 2006 and 2011. Analyses were stratified based on maternal pre-pregnancy BMI class. For each BMI class, we calculated the rate of neonatal death and stillbirth at each week of gestation from 34 to 41 weeks. A composite risk of perinatal mortality associated with 1 week of expectant management was estimated combining the stillbirth rate of the current week and the neonatal death rate of the following week. This was compared with the rate of neonatal death of the current week.

Results: After all exclusions, 2,149,771 births remained for analysis. In the normal weight group, stillbirth risk increased from 0.8 per 10,000 births at 34 weeks to 5.7 per 10,000 births at 42 weeks, whereas the neonatal death risk decreased from 76.5 per 10,000 births at 34 weeks to 30.4 per 10,000 births at 42 weeks, there were no differences between expectant management and delivery for any gestational week. In the obese group, stillbirth risk increased from 1.8 per 10,000 births at 34 weeks to 10.5 per 10,000 births at 42 weeks, whereas the neonatal death risk decreased from 67.7 per 10,000 births at 34 weeks to 26.2 per 10,000 births at 42 weeks, the perinatal mortality risk favored delivery at 39 weeks (RR: 1.17; 99% CI: 1.01–1.36) and not thereafter. In contrast, in the morbidly obese group, stillbirth risk increased from 8.8 per 10,000 births at 34 weeks to 83.7 per 10,000 births at 42 weeks, whereas the neonatal death risk decreased from 63.6 per 10,000 births at 34 weeks to 15.5 per 10,000 births at 42 weeks, the perinatal mortality risk favored delivery from 38 weeks (RR: 1.53; 99% CI: 1.16–2.02) through 41 weeks (RR: 5.39; 99% CI: 1.83–15.88).

Conclusion: The findings reported here suggest that delivery by 38 weeks in gestation minimizes perinatal mortality in pregnancies complicated by maternal morbid obesity.