Maternal BMI and preterm birth: A systematic review of the literature with meta-analysis

Abstract

Objectives. To examine the association between high prepregnancy maternal body mass index (BMI) and the risk of preterm birth (PTB).

Methods. A systematic review of the literature. We included cohorts and case-control studies published since 1968 that examined the association between BMI and PTB of all types, spontaneous (s), elective and with ruptured membranes (PPROM) in three gestational age categories: general (<37 weeks), moderate (32–36 weeks) and very (<32 weeks) PTB.

Results. 20,401 citations were screened and 39 studies (1,788,633 women) were included. Preobese (BMI, 25–29.9) and obese I (BMI, 30–34.9) women have a reduced risk for sPTB: AOR = 0.85 (95% CI: 0.80–0.92) and 0.83 (95% CI: 0.75–0.92), respectively. Their risk for moderate PTB was 1.20 (95% CI: 1.04–1.38) and 1.60 (95% CI: 1.32–1.94), respectively. Obese II women (BMI, 35–40) have an increased risk for PTB in general (AOR = 1.33, 95% CI: 1.12–1.57) moderate (AOR = 2.43, 95% CI: 1.46–4.05) and very PTB (AOR = 1.96, 95% CI: 1.66–2.31). Obese III women (BMI > 40) have an even higher risk for very PTB (AOR = 2.27, 95%CI: 1.76–2.94). High BMI does not modify the risk for PPROM and increases the risk for elective PTB.

Conclusions. High maternal BMI may have different effects on different types of PTB.

Keywords:

• Body mass index
• obesity
• premature birth
• preterm labor
• overweight
• adiposity
• literature review
• meta-analysis

Acknowledgements

The authors are grateful to the following authors for providing additional information and data from their original studies: doctors Haim A. Abenhaim, Patricia Dietz, V. Marsoosi, Ellen Aagaard Nøhr, Kimberly O'Brien, Suezanne T. Orr, Alayne Ronnenberg, Laura Schieve, Vitool Lohsoonthorn and Zahra Yekta. The authors thank Cayce Owens for providing demographic details of the Nashville, TN cohort.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.