Prepregnancy body mass index and the occurrence of severe hypertensive disorders of pregnancy

Background: Prepregnancy overweight is a risk factor for mild preeclampsia and mild transient hypertension of pregnancy. Its association with severe subtypes of these disorders has received less attention. Methods: To assess the association of prepregnancy body mass index (BMI) with severe and mild preeclampsia and transient hypertension of pregnancy, we used data from a 1958-1964 prospective cohort study of 38,188 pregnant women receiving care at 12 U.S. hospitals. Results: There was a monotonic, dose-response relation between prepregnancy BMI and risk of both severe and mild preeclampsia, as well as the risk of severe and mild transient hypertension of pregnancy. Compared with white women with a BMI of 20, the odds ratios for severe preeclampsia at BMI values of 25 and 30 in white women were 1.7 (95% confidence interval = 1.1-2.5) and 3.4 (2.1-5.6), respectively, and 2.1 (1.4-3.2) and 3.2 (2.1-5.0) in black women. The effect of BMI on risk of severe preeclampsia was similar to its effect on mild disease. Compared with the same referent, odds ratios for severe transient hypertension of pregnancy at BMI values of 25 and 30 in white women were 3.6 (2.0-6.5) and 8.8 (4.4-18), respectively, and 3.0 (1.6-5.8) and 4.9 (2.5-9.6) in black women. Overweight was a stronger risk factor for severe than for mild transient hypertension. Conclusions: Incidence of both mild and severe hypertensive disorders of pregnancy rises with increasing BMI. Escalating obesity rates may increase pregnancy hypertensive disorders and ensuing perinatal morbidity.