Does the effect of air pollution on pregnancy outcomes differ by gender? A systematic review

Gender is known to influence pregnancy outcomes. Recent studies have reported an association between air pollution exposure and adverse pregnancy outcomes, but gender differences have not been considered. In order to assess the current evidence of the interactive effects between gender and air pollution on pregnancy outcomes we undertook a systematic literature review. Using a comprehensive list of keywords, English language articles published between 1966 and 2005 were retrieved from major databases. Additional information on gender was obtained from the study authors. Studies were included if they contained well-defined measurements of ambient air pollutants, investigated pregnancy outcomes and reported estimates by gender. In total 11 studies were included. The quality of the studies was assessed using the framework in Systematic Reviews in Health Care Meta-analysis in context and Bracken's Guidelines. Of the 11 studies, four evaluated low birth weight (LBW); one each evaluated very low birth weight and fetal growth and six examined preterm birth (PTB). Females were at higher risk of LBW: adjusted odds ratios (AOR) ranged from 1.07 to 1.62. Males were at higher risk for PTB: AORs ranged from 1.11 to 1.20. In addition, there was some evidence to suggest that the effect of air pollution on LBW is differential by gender; however, the evidence was available only from four studies. This is the first systematic review to consider gender effect. Further high quality studies are needed to establish whether these findings prevail.