Ambient outdoor air pollutants and sex ratio of singletons born after in vitro fertilization: the effect of single blastocyst transfer.

OBJECTIVE

To evaluate the impact of air pollution on the sex ratio in singletons after IVF treatment and to evaluate the influence of the number of and the developmental stage of transferred embryos on the sex ratio.

DESIGN

Retrospective cohort study.

SETTING

University-affiliated IVF unit.

PATIENT(S): A total of 7,004 singletons born after fresh transfer or frozen-thawed embryo transfer (FET) between January 2013 and December 2017.

INTERVENTION(S): None.

MAIN OUTCOME MEASURE(S): Male-to-female ratio in live-born singletons.

RESULT(S): The estimated medians (interquartile range) of particle matter (PM)10, PM2.5, CO, NO2, O3, and SO2 at the IVF site were 51.4 (39.5-64.6), 27.7 (20.7-37.4), 0.62 (0.5-0.72), 32.5 (25.4-40.1), 79.6 (63.3-96.6), and 11.9 (9.3-15.9) μg/m3, respectively. Multivariate analysis indicated that SO2 was the only pollutant clearly associated with sex ratio. In singletons from single blastocyst transfer (SBT), as indicated by the generalized additive model, the SO2 concentration and sex ratio showed an inverted-U-shape association. In singletons after non-SBT, a monotonic decreasing in the sex ratio was observed with increased SO2 concentration. Compared with the referent category (SO2 < 7.57 μg/m3), the sex ratio at the 5th decile of SO2 (10.81-11.94 μg/m3) was increased by 2.1-fold (95% confidence interval [CI], 1.3-3.14) after adjusting covariates. In singletons born from non-SBT, the sex ratio significantly decreased only in the 9th (odds ratio = 0.69; 95% CI, 0.53-0.90) and 10th (OR = 0.74, 95% CI, 0.56-0.98) deciles.

CONCLUSION(S): Low concentrations of SO2 showed an association with increased sex ratio in singletons of SBT, while in singletons born from another ET system the sex ratios did not show an association at low concentrations of SO2.