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Meta-Analysis
. 2010 Jul 20:341:c3428.
doi: 10.1136/bmj.c3428.

Overweight and obesity in mothers and risk of preterm birth and low birth weight infants: systematic review and meta-analyses

Sarah D McDonald  1 , Zhen Han, Sohail Mulla, Joseph Beyene; Knowledge Synthesis Group
Collaborators, Affiliations
Meta-Analysis

Overweight and obesity in mothers and risk of preterm birth and low birth weight infants: systematic review and meta-analyses

Sarah D McDonald et al. BMJ. .

Abstract

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.

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Conflict of interest statement

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.

Figures

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Fig 1 Study selection process
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Fig 2 Forest plot of risk of preterm birth before 37 weeks in overweight and obese women compared with women of normal weight in cohort studies. BMI=body mass index
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Fig 3 Forest plot of risk of induced preterm birth before 37 weeks in overweight and obese women compared with women of normal weight in cohort studies. BMI=body mass index
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Fig 4 Forest plot of risk of having an infant of low birth weight (<2500 g) in overweight and obese women compared with women of normal weight in cohort studies. BMI=body mass index
See this image and copyright information in PMC

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