Mounting evidence indicates air pollution (AP) is adversely associated with birth outcomes, but few studies characterize the association with fecundity. We evaluated the association between long-term ambient AP and outcomes in women undergoing in vitro fertilization (IVF). This study takes advantage the known date of pregnancy attempt in IVF and investigates if type of infertility acts as a modifier of the AP-live birth association. Clinical data on women initiating their 1st autologous IVF cycle in 2012-13 were obtained from four US clinics. Annual average exposure prior to IVF start were estimated at residential address using a national spatial model that used land use regression and universal kriging to estimate particulate matter ≤2.5 (PM2.5), PM10, and nitrogen dioxide (NO2). Modified Poisson regression was used to measure the association between AP and fertilization, pregnancy, pregnancy loss, and live birth. Additive effect modification (EM) of AP and live birth by type of infertility (diminished ovarian reserve (DOR), male, ovulation, tubal) was evaluated using relative excess risk due to interaction (RERI). Higher exposure to PM2.5, by IQR-unit, was associated with a lower likelihood of live birth (RR:0.96, 95%CI:0.90-1.02) and higher likelihood of pregnancy loss (RR:1.09, 95%CI: 0.93-1.26). Results were similar for PM10 and NO2. RERI analysis resulted in negative values, indicating lower likelihood of live birth with EM on an additive scale comparing high AP and DOR (PM2.5,PM10,NO2, all p<0.01) or high AP and male infertility (PM2.5,PM10,NO2, all p<0.001) with low AP and no DOR or male factor, respectively. Despite suggestive but uncertain findings for the association between AP and IVF outcomes, we found an indication of synergistic effects of AP and DOR or male infertility on the likelihood of live birth in women undergoing IVF. This suggests that DOR and male infertility should be further explored in future research evaluating effect of AP on fecundity.