Prepregnancy body mass index and risk of preterm birth: Association heterogeneity by preterm subgroups

Margaret G. Parker, Fengxiu Ouyang, Colleen Pearson, Matthew W. Gillman, Mandy B. Belfort, Xiumei Hong, Guoying Wang, Linda Heffner, Barry Zuckerman, Xiaobin Wang

Research output: Contribution to journalArticle


Background: To evaluate the association between prepregnancy body mass index (BMI) is associated with early vs. late and medically-induced vs. spontaneous preterm birth (PTB) subtypes.Methods: Using data from the Boston Birth Cohort, we examined associations of prepregnancy BMI with 189 early (<34 completed weeks) and 277 late (34-36 completed weeks) medically-induced PTBs and 320 early and 610 late spontaneous PTBs vs. 3281 term births (37-44 weeks) in multinomial regression. To assess for mediation by important pregnancy complications, we performed sequential models with and without hypertensive disorders of pregnancy, chorioamnionitis, and gestational diabetes.Results: Prevalence of prepregnancy obesity (BMI ≥ 30.0 kg/m2) was 28% among mothers with medically-induced PTBs, 18% among mothers with spontaneous PTBs, and 18% among mothers with term births (p = <0.001). After adjustment for demographic and known risk factors for PTB, prepregnancy obesity was associated with higher odds of both early [OR 1.78 (1.19, 2.66)] and late [OR 1.49 (1.09, 2.04)] medically-induced PTB. These effect estimates were attenuated with inclusion of hypertensive disorders of pregnancy and gestational diabetes. For spontaneous deliveries, prepregnancy obesity was associated with decreased odds of PTB (0.76 [0.58, 0.98]) and underweight was nearly associated with increased odds of PTB (1.46 [0.99, 2.16]).Conclusion: Prepregnancy obesity is associated with higher risk of medically-induced, but not spontaneous PTB. Hypertensive disorders of pregnancy and gestational diabetes appear to partially explain the association between prepregnancy obesity and early and late medically-induced PTB.

Original languageEnglish (US)
Article number153
JournalBMC pregnancy and childbirth
Issue number1
StatePublished - Apr 30 2014


  • Late preterm birth
  • Maternal obesity
  • Medically-induced preterm birth
  • Prepregnancy BMI
  • Spontaneous preterm birth

ASJC Scopus subject areas

  • Obstetrics and Gynecology

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