Ambient ozone exposure during preconception and gestation periods and birth weight: when is the critical window?

Abstract

Background: Prenatal exposure to ozone has been associated with lower birth weight. Yet few studies have included the preconception period. Moreover, the critical window of prenatal ozone exposure remains unclear. We aim to examine the association of ambient ozone exposure during preconception and gestation periods with birth weight, and to identify critical exposure windows.Methods: The study included 102 pregnant women at admission for delivery in Anzhen Hospital from July to December 2017 in Beijing, China. We collected information on participants’ demographics, health habits, residential address, and living environment. If participants worked before and/or during pregnancy, work addresses and duration at work on typical workdays were asked. Bi-weekly average ambient ozone levels were estimated for home and work addresses using a validated land use regression model. We weighted the time (hours) at home and work to estimate participants’ ozone exposure levels from 3 months before conception to the end of pregnancy. Birth weight, gestational age, sex, and maternal prenatal care history were extracted from medical records. We used distributed lag non-linear models to examine the association of monthly average ozone exposure with sex- and gestational age-adjusted birth weight z score and to identify critical exposure windows.Results: After adjusting for maternal age, pre-pregnancy body mass index, ethnicity, family income, and season of birth, two critical windows were identified: Birth weight z score was 0.18 (95% confidence interval [CI]: -0.35, -0.01) lower with each 10 ug/m3 increases of ozone exposure during 2 months before conception, and 0.12 (95% CI: -0.23, -0.01) lower with exposures during the 5th month of pregnancy. No statistically significant association was observed during other months in the preconception and gestation periods.Conclusions: High levels of ambient ozone exposures during two months before conception and around 5th months of gestation may be associated with lower birth weight.