Ambient Air Pollution and Risk of Pregnancy Loss among Women Undergoing Assisted Reproduction

Abstract

TPS 742: Adverse birth outcomes 1, Exhibition Hall, Ground floor, August 27, 2019, 3:00 PM - 4:30 PM Background/Aim: Accumulating evidence suggests that air pollution increases pregnancy loss; however, most previous studies have focused on spontaneous pregnancies where the date of conception and implantation is unknown. Methods: We included 275 women (345 human chorionic gonadotropin (hCG)-confirmed pregnancies) undergoing assisted reproduction at a New England fertility center. We estimated daily nitrogen dioxide (NO2), ozone (O3), fine particulate matter <2.5 µm (PM2.5), and black carbon (BC) exposures using validated spatiotemporal models from first positive hCG test until day of failure or live birth. Air pollution exposures were averaged over the past week and the whole pregnancy. Adjusted Cox proportional hazards models were used to model time to pregnancy loss (post-implantation days) to estimate hazard ratios (HRs) corresponding to an interquartile range (IQR) increase in pollutant concentration. We tested for violation of proportional hazards by considering an interaction between post-implantation days (<30 days vs. ≥30 days) and air pollution. Results: The incidence of pregnancy loss was 29% (n=99) with a median (IQR) time to loss of 21 (11, 30) days post-implantation. Average past week exposures to NO2, O3, PM2.5, and BC were not associated with time to pregnancy loss. Overall pregnancy exposure to NO2 was not associated with pregnancy loss; however, there was a statistically significant interaction with time (p-for-interaction=0.01). Specifically, an IQR increase in exposure to NO2 was positively associated with pregnancy loss after 30 days (HR=1.23, 95% CI: 1.09, 1.41), but not in the first 30 days post-implantation (HR=0.84, 95% CI: 0.66, 1.08). Overall pregnancy exposure to O3, PM2.5, and BC were not associated with pregnancy loss regardless of timing. Models evaluating joint effects of all pollutants yielded similar findings. Conclusion: Higher exposure to NO2 during pregnancy was associated with increased risk of pregnancy loss after 30 days post-implantation. Timing of exposure to pregnancy loss is important to consider.