Identifying critical windows and sex-specific effects of periconceptional exposure to fine particulate matter and temperature on fetal growth trajectories: A longitudinal birth cohort study.

The periconceptional windows of susceptibility, sex-specific differences, and joint effects of air pollution and ambient temperature on fetal growth trajectories (FGTs) remain inadequately characterized. We enrolled 1,273 pregnant women from the Ma'anshan Early Birth Cohort. FGTs were constructed using group-based trajectory modeling (GBTM) based on serial ultrasound measurements of biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), femur length (FL), and estimated fetal weight (EFW). Multinomial logistic regression was used to assess the associations between PM2.5 and temperature during exposure windows and FGTs. Distributed lag nonlinear models (DLNMs) were applied to identify periconceptional windows for week-specific associations with slow growth trajectories. Sex-stratified analyses were conducted. Joint effects were evaluated using the relative excess odds (REOI) and attributable proportion (AP). Each 5 μg/m3 increase in PM2.5 exposure was associated with higher odds of slow BPDZ trajectory during preconception (RRR: 1.076, 95% CI: 1.008-1.149), early pregnancy (RRR: 1.173, 95% CI: 1.026-1.341), and the periconceptional period (RRR: 1.114, 95% CI: 1.018-1.219). Heat exposure ( > 95th percentile) was inversely associated with the odds of slow ACZ and BPDZ trajectories during weeks -2 to 13 and weeks -13 to 6, respectively. Similarly, cold exposure ( < 5th percentile) was inversely associated with the odds of slow trajectories, particularly for ACZ during early pregnancy and BPDZ during gestational weeks 6-15. The associations of PM2.5 and temperature exposures with slow trajectories were more pronounced among female fetuses compared to males. Our findings suggest that week-specific windows of susceptibility for intrauterine fetal growth to ambient PM2.5, heat, and cold exposures occur primarily during the periconceptional period. Reducing PM2.5 exposure during the preconception and early pregnancy periods may help protect fetal growth, whereas the associations observed for heat and cold exposure should be interpreted cautiously and warrant further investigation.