Clinical bottom line

Risk of pre-eclampsia generally doubles with each 5-7 kg/sq metre increase in pre-pregnancy body mass index.

Background

Maternal obesity is an important risk factor for the development of pre-eclampsia. This paper conducts a systematic review to quantify the association between pre-pregnancy body mass index and risk of pre-eclampsia in order to better identify those at highest risk.

Reference

TE O'Brien et al. Maternal body mass index and the risk of preeclampsia: a systematic overview. Epidemiology 2003 14: 368-374.

Systematic review

Studies were identified through searches of MEDLINE, Embase (1980-2002) and references from review articles. English language cohort studies with at least 50 participants were included.

Results

Thirteen studies with 1,390,226 women were identified. Study size ranged from 281 to 878,680.

Five studies excluded women with chronic hypertension, four excluded women with diabetes mellitus and nine excluded women with multiple gestations.

Categories of body mass index varied between studies (within the range of <19 to >35 kg/sq metre). All but one study defined preeclampsia using established criteria, which includes a blood pressure of greater or equal to 140/90 mmHg or rise in systolic blood pressure of >30 mmHg or diastolic blood pressure of >15 mmHg after 20 weeks gestation.

The risk of preeclampsia typically doubled for each 5-7 kg/m2 increase in body mass index.

This risk was also observed in studies that excluded women with chronic hypertension, diabetes or multiple gestations.

Comment

The authors chose (a priori) not to calculate a summary risk estimate because categories of body mass index varied between studies. Nevertheless, considering all 43 categories of body mass index, the risk of preeclampsia rose by 0.54% (CI 0.27 to 0.80) for each 1 kg/sq metre increase in body mass index.