Air Pollution and Adverse Pregnancy Outcomes: What is the Role of Gender? A Systematic Review

Abstract

SAA5-O-05 Introduction: Gender differences in pregnancy outcomes, eg, low birth weight (LBW), preterm birth (PTB), and fetal growth retardation are well established. Recent studies on air pollution and adverse pregnancy outcomes suggest an increase in risk, albeit small. We undertook a systematic review to study the interaction between gender and air pollution on pregnancy outcomes. Methods: English language articles were retrieved from Medline, Embase, Science Citation Index, and other environmental databases using a comprehensive list of key words relating to gender, air pollution, and pregnancy outcomes (1966–2005). Studies were included if: Exposure measurements were well defined: personal monitoring, approximation from ambient levels, modelled estimates and proximity to pollution sources; Pollutants were specified; Effects on pregnancy outcomes were reported; Effect estimates were reported by gender. Studies were excluded if they included accidental or occupational exposures and multiple births. A tailored checklist based on Bracken's Guideline for Observational Studies, was used to assess methodologic quality. Quality was assessed based on the applicability of the findings and validity of the individual study results. We had concern about exposure measurements in 2 studies while some others did not adjust for socioeconomic status and maternal smoking. Overall the quality of the included studies was considered satisfactory. Results: A total of 11 studies, conducted between 1986 and 2003, were included. Of these, 4 evaluated LBW; one each evaluated very low birth weight (VLBW) and fetal growth, and 6 examined PTB. PTB studies were more homogeneous in terms of study design and analysis than the LBW studies. Female babies were at higher risk of LBW (AORs ranged from 1.07 to 1.62) and male babies were found to be at higher risk for PTB (AORs ranged from 1.11 to 1.20) from the adjusted logistic models. In addition, there was some evidence of an interaction between gender and air pollution for LBW when the highest and lowest exposure categories were compared separately for male and female babies. The risk of LBW, which is commonly high for female babies, was higher in males after accounting for interaction; however, the results were not statistically significant. Discussion and Conclusions: This review provides some limited evidence of an interaction between air pollution and gender on pregnancy outcomes. Any interactive effect should be interpreted with caution in light of study limitations, such as exposure misclassification, multiple comparisons, and residual confounding. Further studies using high quality datasets are needed to ascertain the effect.