Residential proximity to major roads and fecundability in a preconception cohort

Background: Emerging evidence from animal and human studies indicates that exposure to traffic-related air pollution may adversely affect fertility. Methods: Among 7,342 female pregnancy planners from the United States and 1,448 from Canada, we examined the association between residential proximity to major roads and fecundability, the per-cycle probability of conception. From 2013 to 2019, women 21-45 years old who were trying to conceive without fertility treatment completed an online baseline questionnaire and follow-up questionnaires every 8 weeks for up to 12 months or until pregnancy. We geocoded residential addresses reported at baseline and during follow-up, and calculated distance to nearest major roads and length of major roads within buffers of 50, 100, 300, and 400 meters around the residence as proxies for traffic-related air pollution. We used proportional probabilities regression models to estimate fecundability ratios (FRs) and 95% confidence intervals (CIs), adjusting for individual- and neighborhood-level characteristics. Results: In the United States, the FR comparing women who lived <50 meters with those who lived <greater than or equal to>400 meters from the closest major road was 0.88 (95% CI = 0.80, 0.98). The association among Canadian women was similar in magnitude, but less precise (FR = 0.93; 95% CI = 0.74, 1.16). Likewise, length of major roads within buffers of 50 and 100 meters was associated with lower fecundability in both countries; associations were attenuated within larger buffers. Conclusions: These results are consistent with the hypothesis that traffic-related air pollution or other near-road exposures may adversely affect fecundability.