Although e-cigarette aerosol contains similar toxicants to combustible cigarettes, few studies have examined the association between e-cigarettes and fecundability. We assessed the association between e-cigarettes and fecundability, overall and by combustible cigarette smoking history, in a cohort of 4,586 North American women (21-45 years) enrolled 2017-2020 in Pregnancy Study Online (PRESTO), a web-based prospective preconception study. Women reported current and former e-cigarette use, and completed bimonthly follow-up questionnaires until self-reported pregnancy or censoring. Fecundability ratios (FRs) and 95% confidence intervals (CIs) were calculated using proportional probabilities models, controlling for potential confounders. Overall, 17% of women had ever used e-cigarettes and 4% were current users. Compared with never use of e-cigarettes, current e-cigarette use was associated with slightly lower fecundability (FR: 0.84, 95% CI: 0.67, 1.06). Compared with current non-users of e-cigarettes and combustible cigarettes, FRs were 0.83 (95% CI: 0.54, 1.29) for current dual-users of e-cigarettes and cigarettes, 0.91 (95% CI: 0.70, 1.18) for current e-cigarette users who were non-smokers, and 1.01 (95% CI: 0.85, 1.20) for current cigarette smokers who were not e-cigarette users. Current e-cigarette use was associated with slightly reduced fecundability, but estimates of its independent and joint associations with combustible cigarette smoking were inconsistent and imprecise.
