Objective To estimate the association between maternal body mass index (BMI) and risk of spontaneous preterm delivery (sPTD) and elective preterm delivery (ePTD) in singleton and multiple pregnancies.
Design Retrospective cohort study.
Setting Electronic records of all deliveries from 2009 through 2013 in a tertiary university hospital were abstracted for demographic and obstetrical information.
Participants A total of 38 528 deliveries were included. Participants with missing data were excluded from the study. BMI was calculated from the measurement of height and weight at the first prenatal visit and categorised. Sonographic confirmation of gestational age was standard.
Outcome measures Primary outcomes, sPTD and ePTD in singleton and multiple pregnancies, were evaluated by multinomial logistic regression analyses, stratified by parity, controlling for confounding variables.
Results Overall rate of PTD was 5.9%, from which 2.7% were sPTD and 3.2% ePTD. The rate of PTD was 50.4% in multiple pregnancies and 5.0% in singleton pregnancies. The risk of sPTD was increased in obese nulliparas (adjusted OR (aOR) 2.8, 95% CI 1.7 to 4.4) and underweight multiparas (aOR 2.2, 95% CI 1.3 to 3.8). The risk of ePTD was increased in underweight nulliparas (aOR 1.8; 95% CI 1.04 to 3.4) and severely obese multiparas (aOR 1.4, 95% CI 1.02 to 3.8).
Severe obesity increased the risk of both sPTD (aOR 1.4; 95% CI 1.01 to 2.1) and ePTD (aOR 1.4; 95% CI 1.1 to 1.8) in singleton pregnancies. Obesity did not influence the rate of either sPTD or ePTD in multiple pregnancies.
Conclusion Maternal obesity is an independent risk factor for PTD in singleton pregnancies but not in multiple pregnancies. Obesity and nulliparity increase the risk of sPTD, whereas obesity and multiparity increase the risk of ePTD.
- obesity in pregnancy
- iatrogenic preterm birth
- spontaneous preterm birth
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Part of this work was submitted as an abstract to the 63rd Annual Meeting of Society of Gynecologic Investigation 2016, Montreal, Canada.
Contributors AV and MT: conceived and designed the research; AV: analysed the data and wrote the manuscript with input from ND and MT; AM: prepared the initial data set, defined and classified the variables; SS: provided clinical governance and oversaw data collection. All authors provided feedback on the manuscript drafts and approved the final version.
Competing interests None declared.
Patient consent Detail has been removed from this case description/these case descriptions to ensure anonymity. The editors and reviewers have seen the detailed information available and are satisfied that the information backs up the case the authors are making.
Ethics approval Coombe Women and Infants University Hospital Research Ethics Committee (ref 004-013).
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement No additional data available.
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