Overweight and obesity in mothers and risk of preterm birth and low birth weight infants: systematic review and meta-analysesBMJ 2010; 341 doi: https://doi.org/10.1136/bmj.c3428 (Published 20 July 2010) Cite this as: BMJ 2010;341:c3428
- Sarah D McDonald, associate professor1,
- Zhen Han, associate professor2,
- Sohail Mulla, student3,
- Joseph Beyene, associate professor and senior scientist4
- on behalf of the Knowledge Synthesis Group
- 1McMaster University, Division of Maternal-Fetal Medicine, Departments of Obstetrics and Gynecology, Diagnostic Imaging, and Clinical Epidemiology and Biostatistics, Hamilton, ON, L8N 3Z5 Canada
- 2First Affiliated Hospital of Xi’an Jiao Tong University, Department of Obstetrics and Gynecology, Xi’an, Shaanxi Province, People’s Republic of China
- 3McMaster University, Faculty of Health Sciences
- 4University of Toronto, Research Institute of The Hospital for Sick Children and Dalla Lana School of Public Health, Toronto, ON, Canada
- Correspondence to: S D McDonald
- Accepted 7 April 2010
Objective To determine the relation between overweight and obesity in mothers and preterm birth and low birth weight in singleton pregnancies in developed and developing countries.
Design Systematic review and meta-analyses.
Data sources Medline and Embase from their inceptions, and reference lists of identified articles.
Study selection Studies including a reference group of women with normal body mass index that assessed the effect of overweight and obesity on two primary outcomes: preterm birth (before 37 weeks) and low birth weight (<2500 g).
Data extraction Two assessors independently reviewed titles, abstracts, and full articles, extracted data using a piloted data collection form, and assessed quality.
Data synthesis 84 studies (64 cohort and 20 case-control) were included, totalling 1 095 834 women. Although the overall risk of preterm birth was similar in overweight and obese women and women of normal weight, the risk of induced preterm birth was increased in overweight and obese women (relative risk 1.30, 95% confidence interval 1.23 to 1.37). Although overall the risk of having an infant of low birth weight was decreased in overweight and obese women (0.84, 0.75 to 0.95), the decrease was greater in developing countries than in developed countries (0.58, 0.47 to 0.71 v 0.90, 0.79 to 1.01). After accounting for publication bias, the apparent protective effect of overweight and obesity on low birth weight disappeared with the addition of imputed “missing” studies (0.95, 0.85 to 1.07), whereas the risk of preterm birth appeared significantly higher in overweight and obese women (1.24, 1.13 to 1.37).
Conclusions Overweight and obese women have increased risks of preterm birth and induced preterm birth and, after accounting for publication bias, appeared to have increased risks of preterm birth overall. The beneficial effects of maternal overweight and obesity on low birth weight were greater in developing countries and disappeared after accounting for publication bias.
We thank Elizabeth Uleryk, chief librarian at The Hospital for Sick Children, Toronto, Canada, for her help in developing the search strategy.
Members of Knowledge Synthesis Group on determinants of preterm birth/low birthweight: Prakesh Shah, associate professor, Department of Paediatrics, Mount Sinai Hospital and Department of Health Policy, Management and Evaluation, University of Toronto, Toronto, Canada; Arne Ohlsson, professor emeritus, Department of Paediatrics, Mount Sinai Hospital and Departments of Paediatrics, Obstetrics and Gynaecology, and Health Policy, Management and Evaluation, University of Toronto, Canada; Vibhuti Shah, associate professor, Department of Paediatrics, Mount Sinai Hospital and Department of Health Policy, Management and Evaluation, University of Toronto, Toronto, Canada; Kellie E Murphy, associate professor, Department of Obstetrics and Gynecology, Mount Sinai Hospital and University of Toronto, Canada; Sarah D McDonald, associate professor, Division of Maternal-Fetal Medicine, Departments of Obstetrics and Gynecology and Diagnostic Imaging, McMaster University, Hamilton, Canada; Eileen Hutton, associate professor, Department of Obstetrics and Gynecology, McMaster University, Hamilton, Canada; Christine Newburn-Cook, associate professor and associate dean of research, Faculty of Nursing, University of Alberta, Edmonton, Canada; Corine Frick, adjunct professor, Faculty of Nursing, University of Calgary, Calgary, Canada; Fran Scott, associate professor, Dalla Lana School of Public Health, University of Toronto and Toronto Public Health, Toronto, Canada; Victoria Allen, associate professor, Department of Obstetrics and Gynaecology, Dalhousie University, Halifax, Canada; and Joseph Beyene, associate professor and John D Cameron endowed chair in genetic epidemiology, McMaster University, Department of Clinical Epidemiology and Biostatistics.
Contributors: All authors conceived and designed the study, analysed and interpreted the data, critically revised the manuscript for important intellectual content, and approved the final versions. SDMcD had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. She drafted the manuscript and is guarantor.
Competing interests: All authors have completed the unified competing interest form and declare that: (1) this work was supported by a Canadian Institute of Health Research (CIHR) operating grant (No KRS 86242), that SDMcD is supported by a CIHR new investigator award, that ZH was supported by a state scholarship fund by the China Scholarship Council, and that JB is supported by a CIHR grant (No 84392); (2) SDMcD, ZH, SM, and JB have no relationships with any companies that might have an interest in the submitted work in the previous 3 years; (3) their spouses, partners, or children have no financial relationships that may be relevant to the submitted work; and (4) SDMcD, ZH, SM, and JB have no non-financial interests that may be relevant to the submitted work. CIHR and the China Scholarship Council had no role in analyses, writing of the report, interpretation of data or the decision to submit the manuscript.
Ethical approval: Not required.
Data sharing: No additional data available.
- Accepted 7 April 2010
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