Individual and joint effect of indoor air pollution index and ambient particulate matter on fetal growth: A prospective cohort study

Background: Limited studies have examined the effect of prenatal exposure to particulate matter with diameter of <2.5 μm (PM2.5) and <1 μm (PM1) on fetal growth using ultrasound measurements with inconsistent results. No study has evaluated the joint effect of the indoor air pollution index and ambient particulate matter on fetal growth. Methods: We conducted a prospective birth cohort study in Beijing, China in 2018, including 4319 pregnant women. We estimated prenatal PM2.5 and PM1 exposure using a machine-learning method and calculated the indoor air pollution index based on individual interviews. Gender-and gestational age-Adjusted Z-score of the abdominal circumference (AC), head circumference (HC), femur length (FL) and estimated fetal weight (EFW) was calculated and then undergrowth was defined. A generalized estimating equation was used to evaluate the individual and joint effect of indoor air pollution index, PM2.5 and PM1 on fetal Z-score and undergrowth parameters. Results: One unit increase in the indoor air pollution index was associated with-0.044 (95% CI:-0.087,-0.001) and-0.050 (95% CI:-0.094,-0.006) decrease in the AC and HC Z-scores, respectively. PM1 and PM2.5 were associated with decreased AC, HC, FL and EFW Z-scores, and higher risk of undergrowth. Compared with exposure to lower PM1 (≤ median) and no indoor air pollution, those exposed to higher PM1 (> median) and indoor air pollution had decreased EFW Z-scores (β =-0.152, 95% CI:-0.230,-0.073) and higher risk of EFW undergrowth (RR = 1.651, 95% CI: 1.106, 2.464). Indoor air pollution and ambient PM2.5 exposure had a similar joint effect on the Z-scores and undergrowth parameters of fetal growth. Conclusions: This study suggested that indoor air pollution and ambient PM exposure had individual and joint negative effects on fetal growth.