Ambient air pollution on fecundity and live birth in women undergoing assisted reproductive technology in the Yangtze River Delta of China.

BACKGROUND

Ambient air pollution has adverse effects on the reproductive system. However, inconsistent conclusions were reached from different studies with regard to air pollutants and pregnancy outcomes, especially the livebirth rate in assisted reproductive technology (ART) in different windows of exposure.

METHODS

A retrospective cohort study was conducted on 12,665 women who underwent first fresh or frozen embryo transfer cycle in the Yangtze River Delta of China. Daily average levels of six air pollutants in four different periods were obtained: Period 1 and 2: 90 days or one year prior to oocyte retrieval; Period 3 and 4: the day of oocyte retrieval or one year prior to oocyte retrieval to the day of serum hCG test or to the end of the pregnancy. A multiple logistic regression model was used to investigate the association between air pollutant exposure and pregnancy outcomes. Stratified analyses were conducted to explore potential modifier effects.

RESULTS

The one year exposure window (Period 2) before oocyte retrieval had a more evident negative association with pregnancy outcomes. Each IQR increase in ambient PM (OR: 0.89, 95% CI: 0.84-0.93), PM (OR: 0.82, 95% CI: 0.77-0.87), SO (OR: 0.87, 95% CI: 0.83-0.91) and CO (OR: 0.91, 95% CI: 0.87-0.96) was associated with a respective 11%, 18%, 13% and 9% decrease in the likelihood of live birth. In entire exposure window of Period 4, all air pollutants except for O were associated with a decreased likelihood of live birth. Stratified analyses showed that women undergoing frozen embryo transfer cycles, especially those with two embryos transferred, were more vulnerable to air pollutant exposure.

CONCLUSION

This study indicates a negative association between air pollutant exposure before oocyte retrieval and livebirth rate in ART. The adverse impact was more evident in one year exposure compared to three-month refresh cycle of the gametes. Additional protection from air pollution should be undertaken at least one year before ART, particularly for those with frozen embryo transfer cycles.