[Association between prenatal exposure to PM_2.5 and fetal growth: a prospective cohort study]

Objective: To investigate the association of exposure to PM_2.5 and its constituents during pregnancy and fetal growth and to further identify critical windows of exposure for fetal growth. Methods: We included 4 089 mother-child pairs from the Jiangsu Birth Cohort Study between January 2016 and October 2019. Data of general characteristics, clinical information, daily average PM_2.5 exposure, and its constituents during pregnancy were collected. Fetal growth parameters, including head circumference (HC), abdominal circumference (AC), and femur length (FL), were measured by ultrasound after 20 weeks of gestation, and then estimated fetal weight (EFW) was calculated. Generalized linear mixed models were adopted to examine the associations of prenatal exposure to PM_2.5 and its constituents with fetal growth. Distributed lag nonlinear models were used to identify critical exposure windows for each outcome. Results: A 10 μg/m³ increase in PM_2.5 exposure during pregnancy was associated with a decrease of 0.025 (β=-0.025, 95%CI: -0.048- -0.001) in HC Z-score, 0.026 (β=-0.026, 95%CI: -0.049- -0.003) in AC Z-score, and 0.028 (β=-0.028, 95%CI:-0.052--0.004) in EFW Z-score, along with an increased risk of 8.5% (RR=1.085, 95%CI: 1.010-1.165) and 13.5% (RR=1.135, 95%CI: 1.016-1.268) for undergrowth of HC and EFW, respectively. Regarding PM_2.5 constituents, prenatal exposure to black carbon, organic matter, nitrate, sulfate (SO₄^2-) and ammonium consistently correlated with decreased HC Z-score. SO₄^2- exposure was also associated with decreased FL Z-scores. In addition, we found that gestational weeks 2-5 were critical windows for HC, weeks 4-13 and 19-40 for AC, weeks 4-13 and 23-37 for FL, and weeks 4-12 and 20-40 for EFW. Conclusions: Our findings demonstrated that exposure to PM_2.5 and its constituents during pregnancy could adversely affect fetal growth and the critical windows for different fetal growth parameters are not completely consistent.