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

Margaret G Parker1*, Fengxiu Ouyang2, Colleen Pearson1, Matthew W Gillman34, Mandy B Belfort5, Xiumei Hong67, Guoying Wang67, Linda Heffner8, Barry Zuckerman1 and Xiaobin Wang67

Author Affiliations

1 Department of Pediatrics, Boston Medical Center, Boston University School of Medicine, Boston, USA

2 MOE-Shanghai Key Laboratory of Children’s Environmental Health, Xinhua Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China

3 Obesity Prevention Program, Department of Population Medicine, Harvard Medical School/Harvard Pilgrim Health Care Institute, Boston, USA

4 Department of Nutrition, Harvard School of Public Health, Boston, USA

5 Division of Newborn Medicine, Department of Pediatrics, Children’s Hospital Boston, Harvard Medical School, Boston, USA

6 Center on the Early Life Origins of Disease, Department of Population, Family and Reproductive Health, Johns Hopkins University Bloomberg School of Public Health, Baltimore, USA

7 Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, USA

8 Department of Obstetrics and Gynecology, Boston Medical Center, Boston University School of Medicine, Boston, USA

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BMC Pregnancy and Childbirth 2014, 14:153  doi:10.1186/1471-2393-14-153

Published: 30 April 2014



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.


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.


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]).


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.

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