Increased risk of placental abruption in underweight women.

We sought to determine if there is a relationship between prepregnancy underweight status and placental abruption. We utilized the Missouri maternally linked cohort data files covering the period 1989 through 1997. We estimated the association between prepregnancy underweight subtypes and placental abruption using adjusted odds ratios. Subanalyses were performed to determine whether the amount of weight gained during pregnancy could modify the association. A total of 439,235 singleton pregnancies with 3696 abruptions were analyzed. Underweight mothers had a 40% greater likelihood for placental abruption (odds ratio 1.4; 95% confidence interval 1.3 to 1.5). The risk increased with ascending severity of underweight status (p for trend <0.01). There was a trend toward decreased risk for placental abruption among underweight women with adequate weight gain in pregnancy. Prepregnancy maternal underweight status is associated with placental abruption. This risk may be reduced with adequate weight gain during pregnancy.