Abstract

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. We searched MEDLINE, EMBASE, CINAHL, and LILACS (up to October 2007), and reviews and reference lists from publications, with no language restrictions. We estimated pooled mean differences and odds ratios (OR) with 95% confidence intervals (CI) 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 birthweight and proportion of premature infants.

Results: 58 studies were included; 53 used cohort designs, 23 ascertaining ETS exposure prospectively and 30 retrospectively. Five used case-control designs. In prospective studies, ETS exposure was associated with a 33g reduction (95% CI 16g, 51g) in mean birthweight, and in retrospective studies a 40g reduction (95% CI 26g, 54g). ETS exposure was also associated with an increased risk of low birthweight (birthweight<2,500g; prospective studies: OR 1.32, 95% CI 1.07, 1.63; retrospective studies: OR 1.22, 95% CI 1.08, 1.37). The risk of small-for-gestational age (SGA, <10th centile) birth was significantly associated with ETS exposure only in retrospective studies (OR 1.21, 95% CI 1.06, 1.37). There was no effect of ETS exposure on gestational age.

Conclusions: Exposure of non-smoking pregnant women to ETS reduces mean birthweight by 33g or more, and increases the risk of birth below 2,500g by 22%, but has no clear effect on gestation or the risk of being small-for-gestational-age.