Maternal body mass index, height, and risks of preeclampsia

There is an association between maternal body mass index (BMI) and preeclampsia, but if BMI has an effect on preeclampsia of all severities is debated. If there is an association between maternal height and preeclampsia of all severities is unknown.

In this population-based cohort study including 503,179 nulliparous women, we estimated risks of preeclampsia of different severity in short (<164 cm) and tall (≥172 cm) women, using women of average height (164-171 cm) as reference, and in underweight (BMI: ≤18.4kg/m(2)), overweight (BMI: 25.0-29.9 kg/m(2)), obese class I (BMI: 30.0-34.9kg/m(2)) and obese class II-III (BMI: ≥35.0 kg/m(2)) women, using women with normal weight (BMI: 18.5-24.9kg/m(2)) as reference. Severity of preeclampsia was classified as early (<32 weeks), moderately early (32-36 weeks), and late (≥37 weeks) preeclampsia, or severe preeclampsia and mild to moderate preeclampsia, as defined by diagnostic codes.

Short women had increased risks of all types of preeclampsia, but especially of early disease (adjusted odds ratio (OR) 1.3; 95% confidence interval (CI) 1.2-1.5). The risks of all preeclampsia types increased with BMI, but seemed higher for milder than more severe types of preeclampsia. Obesity class II-III was associated with a four-fold increased risk of mild to moderate preeclampsia (adjusted OR 4.0; 95% CI 3.7-4.4).

A short maternal stature and a high BMI increase risks of preeclampsia of all severities. The associations seem especially strong between short stature and severe types of preeclampsia, and high BMI and mild types of preeclampsia.