Association of extremes of prepregnancy BMI with the clinical presentations of preterm birth.

Abstract

The purpose of this study was to examine associations between the prepregnancy maternal body mass index (BMI) across the 3 clinical presentations of preterm birth (PTB). We conducted a retrospective cohort study of the records of 11,726 women. The World Health Organization International Classification was used to categorize BMI. The primary outcome of the study was PTB (<37 weeks' gestation) presenting as spontaneous preterm labor, preterm premature rupture of the membranes, or a medical indication. We used univariable and multivariable logistic regression analysis to analyze the data (P < .05). We found (1) a significant increase in the overall incidence of PTB at the extremes of BMI, (2) a higher risk for PTB from spontaneous preterm labor at the lower extremes (low plus moderate thinness) of BMI (adjusted odds ratio [aOR], 2.4; 95% confidence interval [CI], 1.4-4.2; P = .003), (3) a higher risk for preterm premature rupture of the membranes at the upper extremes (obese class II plus III) of BMI (aOR, 1.6; 95% CI, 1.1-2.3; P = .02), and (4) a higher risk for a medically indicated PTB at the lower (aOR, 2.8; 95% CI, 1.4-5.6; P = .004) and upper (aOR, 1.5; 95% CI, 1.1-2.2; P = .02) extreme of BMI. Women at the extremes of prepregnancy BMI are at risk for PTB.