Prepregnancy body mass index and the risk of preeclampsia: a meta-analysis of cohort studies

Background: Prepregnancy maternal obesity is an important risk factor for the development of preeclampsia. However, the reports on the incidence of preeclampsia in women with low body mass index (BMI) are controversial. Methods: We searched PubMed up to April 2014 and identified 35 cohort studies reporting an odds ratio (OR) as a common measure for the association between prepregnancy BMI and the risk of preeclampsia. We used a random-effects model to calculate the combined risk estimates due to heterogeneity and also evaluated a potential curve linear association using restricted cubic splines (RCS). Sensitivity meta-regression and subgroup analyses were conducted to explore the possible explanation for heterogeneity. Results: Women with a low BMI compared to those within normal range had 28% lower risk of developing preeclampsia (pooled OR = 0.72, 95% CI 0.66-0.78, p < 0.001). The pooled OR for overweight and obese women were 1.64 (95% CI 1.54-1.76) and 2.86 (95% CI 2.56-3.19), respectively. Specifically, one unit increase in prepregnancy BMI yields a 0.432% (95% CI 0.224-0.640) increase in the prevalence of preeclampsia by restricted cubic spline function. Maternal age, parity, multi-fetal pregnancy, sample size and the source of BMI were not significantly associated with risk estimates on meta-regression and subgroup analyses. Sensitivity analysis revealed that the pooled ORs are stable. Conclusion: Our finding suggested that low prepregnancy maternal BMI was associated with decreased risk of preeclampsia, whereas overweight and obese women had increased risk to the development of preeclampsia.