Poor air quality index on the day of embryo transfer may decrease the rate of embryo transfer success

The objective of this retrospective cohort study was to evaluate whether air quality index (AQI) on the day of embryo transfer (ET) is associated with differences in clinical pregnancy rates (CPR). The study included all patients who underwent either fresh or frozen embryo transfer between June 1 - July 31, 2023 at a single academic fertility centre in New York. During this time, smoke originating from wildfires in Eastern Canada caused significant air pollution in New York. Patients who underwent single euploid embryo transfer were included and analysed separately. The main outcome measure was clinical pregnancy rate (CPR). Secondary outcomes included biochemical pregnancy rate, miscarriage rate, ectopic pregnancy rate, and live birth rate (LBR). Outcomes after ET were compared between three groups stratified by AQI category as defined by the EPA: Good: 0-50, Moderate: 51-100, and Unhealthy: >100. Chi square analyses were used to compare outcomes between groups. There were 190 ETs performed: 142 (74%) when the AQI was Good, 37 (19.5%) when the AQI was Moderate, and 11 (5.8%) when the AQI was Unhealthy. Higher CPRs were observed for ETs performed when AQI was Good vs. Unhealthy (62.0% vs. 27.3%, p = 0.02) and when Moderate vs. Unhealthy (64.9% vs. 27.3%, p = 0.03). There were 127 single euploid embryo transfers (SETs) performed: 96 (75.6%) when the AQI was Good, 23 (18.1%) when the AQI was Moderate, and 8 (6.3%) when the AQI was Unhealthy. Higher CPRs were observed when AQI was Good vs. Unhealthy (70.8% vs. 37.5%, p = 0.052,) although this was not statistically significant. The CPR was not significantly different for SET when AQI was Moderate vs. Unhealthy (69.6% vs. 37.5%, p = 0.11). While the LBR was lower when AQI was Unhealthy, statistical significance was not reached (p = 0.21 for the whole cohort and p = 0.28 for SET). This study found that poor air quality on the day of ET is associated with a decreased CPR. Embryo transfers performed when the AQI is Unhealthy results in decreased CPRs compared to ETs performed when the AQI is Good and Moderate.