Obesity may be a risk factor for stillbirth during pregnancy

1. Pregnant individuals with obesity according to their body mass index (BMI) had an increased risk for stillbirth when compared to pregnant individuals with a normal BMI

Evidence Rating Level: 2 (Good) 

While obesity has been shown to be a risk factor for stillbirths, there may be conflating factors contributing to these findings. Among pregnant people with obesity, advancing gestational age was associated with increased hazard ratios (HRs). A retrospective cohort study was undertaken to examine the effects of additional factors compared to obesity in pregnant people alone as a risk factor for stillbirths. The Better Outcomes Registry and Network (BORN) provided data for antenatal, intrapartum, postpartum, and neonatal outcomes for births that occurred after 20 weeks’ gestation in Ontario, Canada. To understand the relationship between prepregnancy body mass index (BMI) class and stillbirth, multivariable Cox proportional hazard regression analysis was used as it was able to control for possible confounding variables. Logistic regression was also used to examine odds ratios (ORs) and 95% confidence intervals (CIs) for stillbirths. For the analysis, obstetrical complications were treated independently from maternal characteristics. Mediator analyses were used to examine the effects of BMI on stillbirths. The results were modeled to examine whether maternal obesity was the sole risk factor for stillbirth. The data pool for this study included 681 178 births that occurred between 2012 and 2018, of which 1956 were stillbirths. There was an association between Class I obesity and an increased occurrence of stillbirth (adjusted hazard ratio [HR] 1.55, 95% confidence interval [CI] 1.35–1.78). However, class III obesity was associated with an even higher incidence (adjusted HR 1.80, 95% CI 1.44–2.24), and class II with the highest incidence of stillbirths (adjusted HR 2.17, 95% CI 1.83–2.57). Compared to those with a normal BMI, those with obesity as their only risk factor had an increase chance of stillbirth past 37 weeks’ gestation as found by plotting point estimated for odds ratios. Pregnant people experiencing obesity, especially the highest classes, have an increased risk of stillbirths when compared to pregnant people with a normal BMI. This risk further increases with advancing gestational age. Overall, there was a higher risk of stillbirths associated with maternal obesity even after adjusting for prevalent risk factors in this community. 

Click to read the study in CMAJ

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