Review
Obstetrics
Maternal obesity and risk of stillbirth: a metaanalysis

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We conducted this metaanalysis to summarize the available epidemiologic evidence on the relationship between maternal overweight and obesity and the risk of stillbirth. We identified studies from 3 sources: (1) a PubMed search of relevant articles that were published between January 1980 and September 2005, (2) reference lists of publications that were selected from the PubMed search, and (3) reference lists of review articles on obesity and maternal outcomes that were published between 2000 and 2005. We used a Bayesian random effects model to perform the metaanalysis and metaregression. Nine studies were included in the metaanalysis. The unadjusted odds ratios of a stillbirth were 1.47 (95% CI, 1.08-1.94) and 2.07 (95% CI, 1.59-2.74) among overweight and obese pregnant women, respectively, compared with normal-weight pregnant women. The metaregression analysis found no evidence that these estimates were affected by selected study characteristics. Maternal obesity is associated with an increased risk of stillbirth, although the mechanisms to explain this association are not clear.

Section snippets

Search process

Using recommendations from the Meta-analysis of Observational Studies in Epidemiology guidelines,6 we identified studies for possible inclusion in this analysis using 3 sources. First, we searched PubMed from January 1980 to September 2005 using the following criteria: overweight or obesity or body mass index (BMI) or weight gain AND pregnancy or prepregnancy AND risks or effects or complications. From this search, we retrieved the full text for abstracts that mentioned a relationship between

Results

Figure 1 shows the flow diagram of the literature search results. The PubMed search identified 7112 studies; 127 abstracts reported a finding on the relationship between maternal obesity and pregnancy complications from a case-control or cohort study; these articles were retrieved for detailed examination. Of the retrieved articles, 15 studies mentioned stillbirth, fetal death, or perinatal death as an outcome. After reviewing the reference lists of the 127 studies that were retrieved, we

Comment

Based on metaanalysis of the literature, we estimate that the risk of stillbirth is almost twice as high among obese pregnant women compared with normal-weight pregnant women. Because obesity is a modifiable risk with a substantial prevalence in the United States5 and other developed countries, the impact of reducing that exposure can be considerable.

A biologic pathway for the increased risk of stillbirth related to obesity has not been established, but several mechanisms have been proposed.

Acknowledgment

We thank Mark Klebanoff, MD, National Institute of Child Health and Human Development, National Institutes of Health, for his thoughtful review and helpful comments.

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    The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention.

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