Maternal body mass index and post-term birth: a systematic review and meta-analysis

N Heslehurst* (Corresponding Author), R Vieira, L Hayes, L Crowe, D Jones, S Robalino, E Slack, J Rankin

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

38 Citations (Scopus)
11 Downloads (Pure)


Post-term birth is a preventable cause of perinatal mortality and severe morbidity. This review examined the association between maternal body mass index (BMI) and post-term birth at ≥42 and ≥41 weeks' gestation. Five databases, reference lists and citations were searched from May to November 2015. Observational studies published in English since 1990 were included. Linear and nonlinear dose-response meta-analyses were conducted by using random effects models. Sensitivity analyses assessed robustness of the results. Meta-regression and sub-group meta-analyses explored heterogeneity. Obesity classes were defined as I (30.0-34.9 kg m-2 ), II (35.0-39.9 kg m-2 ) and III (≥40 kg m-2 ; IIIa 40.0-44.9 kg m-2 , IIIb ≥ 45.0 kg m-2 ). Searches identified 16,375 results, and 39 studies met the inclusion criteria (n = 4,143,700 births). A nonlinear association between maternal BMI and births ≥42 weeks was identified; odds ratios and 95% confidence intervals for obesity classes I-IIIb were 1.42 (1.27-1.58), 1.55 (1.37-1.75), 1.65 (1.44-1.87) and 1.75 (1.50-2.04) respectively. BMI was linearly associated with births ≥41 weeks: odds ratio is 1.13 (95% confidence interval 1.05-1.21) for each 5-unit increase in BMI. The strength of the association between BMI and post-term birth increases with increasing BMI. Odds are greatest for births ≥42 weeks among class III obesity. Targeted interventions to prevent the adverse outcomes associated with post-term birth should consider the difference in risk between obesity classes.

Original languageEnglish
Pages (from-to)293-308
Number of pages16
JournalObesity Reviews
Issue number3
Early online date13 Jan 2017
Publication statusPublished - Mar 2017

Bibliographical note

All authors contributed to the design of the research, acquisition of data and writing of the manuscript. NH and JR obtained funding. NH, RV and LH carried out the analysis. The authors would like to acknowledge Dr Helen Simpson at South Tees Hospitals NHS Foundation Trust and Dr Helene Brandon at Gateshead NHS Foundation Trust for their contribution to the clinical relevance and interpretation of this study. Dr Simpson and Dr Brandon are consultant obstetricians with a special interest in maternal obesity and risk management.

This research was part funded by a Medical Research Council and Newcastle University Faculty of Medical Sciences Doctoral Training award for ES. The funders had no role in design and conduct of the study, collection, management, analysis and interpretation of the data and preparation, review or approval of the manuscript.


  • Body Mass Index
  • Body Weight
  • Databases, Factual
  • Female
  • Gestational Age
  • Humans
  • Infant, Newborn
  • Infant, Postmature
  • Mothers
  • Non-Randomized Controlled Trials as Topic
  • Obesity
  • Observational Studies as Topic
  • Pregnancy
  • Pregnancy Complications
  • Socioeconomic Factors
  • Journal Article
  • Meta-Analysis
  • Review


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