Traffic-related air pollution and fetal growth in Eastern Massachusetts, USA

Abstract

Background and Aim: Previous studies have examined the association between prenatal nitrogen dioxide (NO2) —a traffic emissions tracer— and fetal growth based on ultrasound measures during pregnancy. Yet, most have used exposure assessment methods with low temporal resolution, which limits the identification of critical exposure windows given that pregnancy occurs over a relatively short period. Here, we used NO2 data estimated from a high-resolution spatiotemporal model to examine the association between weekly NO2 exposure during pregnancy and fetal growth in a Massachusetts-based cohort. Methods: We used data from 9,446 singleton births at Beth Israel Deaconess Medical Center in 2011-2016. Fetal growth parameters included birth weight, and ultrasound measures of biparietal diameter (BPD), head circumference (HC), femur length, and abdominal circumference. Ultrasound parameters were classified into three distinct gestational periods: 16-23 weeks, 24-31 weeks, and 32+ weeks. We used distributed lag models to estimate the time-varying association between weekly NO2 exposure and fetal growth. All models were adjusted for sociodemographic characteristics, time trends, particulate matter less than 2.5 microns (PM2.5), and temperature. Results: We found that higher NO2 was negatively associated with all fetal growth parameters. The critical window differed depending on the fetal growth parameter and when it was assessed, with associations particularly strong for head parameters. For example, for BPD and HC measured after week 32, the critical exposure window appeared to be around weeks 15-25; a 10-ppb higher NO2 exposure sustained from conception to the time of measurement was associated with a lower mean z-score of -0.26 (95% CI: -0.39, -0.13) and -0.13 (95% CI: -0.25, 0.00) for BPD and HC, respectively. Conclusions: Higher NO2 was associated with smaller fetal growth measures. We identified several critical exposure windows that varied by parameter and timing of measurement. Keywords: air pollution, traffic, nitrogen dioxide, fetal growth, ultrasound, pregnancy, critical window