The Preterm Prediction study: Association between maternal body mass index and spontaneous and indicated preterm birth

Objective: The purpose of this Study was to evaluate the relationship between prepregnancy maternal body mass index and spontaneous preterm birth and indicated preterm birth. Study design: This was a secondary analysis of the Maternal-Fetal Medicine Units Network, Preterm Prediction Study. Patients were classified into categories that were based on their body mass index. Rates of indicated and spontaneous preterm birth were compared. Results: Five hundred ninety-seven (20.5%) of 2910 women were obese. Obese women had fewer spontaneous preterm births at < 37 weeks of gestation (6.2% vs 11.2%: P < .001) and at < 34 weeks of gestation (1.5% vs 3.5%; P = .012). Women with a body mass index of < 19 kg/m(2) had 16.6% spontaneous preterm birth. with a body mass index of 19 to 24.9 kg/m(2) had 11.3% Spontaneous preterm birth, with a body mass index of 25 to 29.9 kg/m(2) had 8.1% spontaneous preterm birth with a body mass index of 30 to 34.9 kg/m(2) had 7.1% spontaneous preterm birth, and with a body mass index of greater than or equal to 35 kg/m(2) had 5.2% spontaneous preterm, birth (P < .0001). Indicated delivery was responsible for an increasing proportion of preterm births with increasing body mass index (P = .001). Obese women had lower rates of cervical length < 25 min (5% vs 8%: P = .012). Multivariable regression analysis confirmed a lower rate of spontaneous preterm birth in obese in-avid women (odds ratio, 0.57: 95% CI 0.39-0.83. P = .003). Conclusion: Obesity before pregnancy is associated with a lower rate of spontaneous preterm birth. (C) 2005 Elsevier Inc. All rights reserved.