Prepregnancy body mass index as an independent risk factor for pregnancy-induced hypertension

Background: Pregnancy-induced hypertension (PIH) plays a major role in the perinatal outcome for mother and neonate. With the rising prevalence of obesity, the role of prepregnancy body mass index (BMI) as an independent risk factor for PIH and a target for preconception care is important to explore. Methods: We completed a retrospective cohort study of 16,582 women who received obstetrical care at a regional medical center and delivered a singleton pregnancy between 2003 and 2006. Clinical data were derived from the electronic medical record. Logistic regression was used to explore the association of demographic characteristics and medical risk factors with the outcome of PIH. Results: Diagnoses of chronic hypertension, prepregnancy diabetes, and gestational diabetes were more likely in women with increasing prepregnancy maternal BMI (p<0.0001). The odds of PIH also increased with BMI, ranging from an odds ratio (OR) of 1.99 (95% confidence interval [CI] 1.73-2.31) for overweight women through OR 4.26 (95% CI 3.37-5.38) for those with a BMI of ≥40kg/m ². Other risk factors for PIH included chronic hypertension (OR 6.57, 95% CI 5.43-7.95), nulliparity (OR 1.89, 95% CI 1.69-2.12), prepregnancy diabetes (OR 2.05, 95% CI 1.33-3.17), and gestational diabetes (OR 1.28, 95% CI 1.04-1.58). The presence of chronic hypertension modified the association between obesity and PIH; for women with chronic hypertension, obesity was not associated with PIH (adjusted OR [aOR] 1.39, 95% CI 0.77-2.50 for BMI 30-34.9; aOR 0.98, 95% CI 0.52-1.87 for BMI 35-39.9; and aOR 1.33, 95% CI 0.73-2.43 for BMI ≥40kg/m²) compared with women with a BMI in the normal range. Conclusions: The risk of PIH rises with maternal prepregnancy BMI independent of other obesity-associated comorbidity. Women with chronic hypertension carry the greatest risk of PIH but incur no obesity-associated increase in risk.