Objective: To determine the effects of environmental tobacco smoke (ETS) exposure on birth outcomes.
Design: A systematic review and meta-analysis was performed in accordance with MOOSE guidelines. MEDLINE, EMBASE, CINAHL and LILACS (up to October 2007), were searched and also reviews and reference lists from publications, with no language restrictions. Pooled mean differences and odds ratios (ORs) with 95% confidence intervals were estimated using data extracted from papers, based on random effect models.
Setting: Comparative epidemiological studies.
Patients: Pregnant women or women who have given birth.
Exposures: Maternal exposure to ETS during pregnancy.
Main outcome measures: Mean birth weight and proportion of premature infants.
Results: 58 studies were included; 53 used cohort designs, 23 ascertaining ETS exposure prospectively and 30 retrospectively; 5 used case–control designs. In prospective studies, ETS exposure was associated with a 33 g (95% CI 16 to 51) reduction in mean birth weight, and in retrospective studies a 40 g (95% CI 26 to 54) reduction. ETS exposure was also associated with an increased risk of low birth weight (birth weight <2500 g; prospective studies: OR 1.32, 95% CI 1.07 to 1.63; retrospective studies: OR 1.22, 95% CI 1.08 to 1.37). The risk of small for gestational age (<10th centile) birth was significantly associated with ETS exposure only in retrospective studies (OR 1.21, 95% CI 1.06 to 1.37). There was no effect of ETS exposure on gestational age.
Conclusions: Exposure of non-smoking pregnant women to ETS reduces mean birth weight by 33 g or more, and increases the risk of birth weight below 2500 g by 22%, but has no clear effect on gestation or the risk of being small for gestational age.
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Contributors: JL-B participated in the conception, design, identifying studies, data collection, study selection, data extraction, analysis, and interpretation of the data; in the writing of the protocol, drafting and revising the article. AS, JB and TC participated in the conception, design, study selection, data extraction, and interpretation of the data; in the writing the protocol, in drafting the article and revising it critically for important intellectual content, and approved the final version to be published.
Funding: This study was internally funded by the University of Nottingham. The sponsor had no role in the study design; in the collection, analysis, and interpretation of data; in the writing of the report; and in the decision to submit the paper for publication.
Competing interests: None declared.