AIR POLLUTION AND REPEATED ULTRASOUND MEASURES OF FETAL GROWTH IN MEXICO CITY

Abstract

Background and Aims: Fetal growth may be affected by maternal air pollution exposure. Among a cohort of pregnant women in Mexico City, we obtained repeated fetal biometry ultrasound data to examine associations between maternal air pollution exposure in early pregnancy and changes in fetal growth. Methods: Information on factors known to impair fetal growth was collected by physical exams and questionnaires in 2010. Repeated ultrasound scans during gestation were performed to measure biometric parameters of the developing fetus [head circumference (HC), abdominal circumference (AC), femur length (FL), and biparietal diameter (BPD)]. Gestational age was estimated from these ultrasound measurements. Using 2009-2010 air pollution data from the city’s atmospheric monitoring network, first trimester citywide averages of PM2.5 were calculated for each individual. We applied linear regression to calculate individual-specific slopes for the four growth parameters. These slopes were used as the outcome in four multivariate linear models with predictors being individual-specific first trimester concentrations of PM2.5; mother’s age and education, and fetal sex. Results: Data were analyzed for 42 women. The average (SD) rates of increase (centimeters/gestational week (cm/wk) for fetal parameters (HC, AC, FL, and BPD) were: 1.01 (0.08), 1.04 (.12), 0.25 (0.02), and 0.28 (0.03) respectively. Point estimates for the association were positive for both HC (.083 cm/wk, p = 0.17, per 10 µg/m3 increment in exposure) and FL (.014 cm/wk, p = 0.43) . Reductions of -.005 cm/wk for BPD (p = 0.82) and -.170 cm/wk for AC (p = .06) per 10 µg/m3 were observed. Conclusions: Fetal parameters may respond to maternal air pollution exposures uniquely, and this response may vary by pollutant and timing of gestational exposure. This analysis of repeated ultrasound measures and first trimester PM2.5 concentrations supports the need for further work examining changes in fetal parameters associated withother pollutant exposures.