Extreme obesity and risk of placental abruption.

BACKGROUND Data on extreme obesity and placental abruption are scarce. This study aimed to determine the association between pre-pregnancy weight and placental abruption and whether pregnancy weight gain impacts this risk. METHODS We used the Missouri maternally linked cohort files (years 1989-1997). Analyses were restricted to singleton live births (n = 461 729). Maternal body mass index (BMI) was classified as normal (18.5-24.9) (referent group), obese [Class 1 (30.0-34.9), Class 2 (35.0-39.9) and extreme or Class 3 (> or =40)]. Pregnancy weight gain categories included: < or =0.22 kg/week (low), 0.23-0.68 kg/week (moderate) and > or =0.69 kg/week (high). Adjusted odds ratios generated from generalized estimating equations for logistic regression models were used to approximate relative risks. RESULTS; Obese women were less likely to have placental abruption than normal weight women (adjusted odds ratio = 0.8, 95% confidence interval 0.7-0.9). The risk was similar regardless of severity of obesity. However, analyses stratified by weight gain during pregnancy indicated that reduced risk was limited to obese women with low or moderate weight gain during pregnancy, although the analyses by subclass of obesity were only statistically significant for women with moderate weight gain. Among women with moderate weight gain, the risk of placental abruption decreased with increasing BMI in a dose-dependent pattern (P < 0.01). CONCLUSIONS Obesity is associated with reduced risk for placental abruption when the weight gain during pregnancy is moderate. These findings underscore the need for further research on the role of nutritional status during pregnancy as a protective factor against placental abruption so that preventive strategies may be appropriately developed.