Air Pollution and Repeated Ultrasound Measurements of Fetal Growth in Mexico City.

Abstract

The possible adverse effect of ambient air pollution on various birth outcomes (e.g., weight, length of gestation) is a global public health concern. However, understanding of prenatal exposure to air pollutants and the process of intrauterine growth is limited. This dissertation addressed research gaps in this area by evaluating maternal air pollution exposure and fetal growth using a novel methodological approach. Overall, the objective of this dissertation was to assess exposure to ozone (O3) and particulate matter less than 2.5 micrometers in aerodynamic diameter (PM2.5) during the first trimester and growth trajectories of four fetal anthropometric parameters [head circumference (HC), biparietal diameter (BPD), abdominal circumference (AC), and femur length (FL)], within a Mexico City cohort of pregnant women. First, a systematic review of the epidemiological literature on maternal exposures to air pollutants and fetal growth, as assessed with data from ultrasound examination of fetal anthropometric parameters, revealed scant and limited research exploring in utero assessment of fetal growth related to prenatal air pollution exposure. Secondly, uncertainty related to the use of repeated ultrasound measurements of fetal parameters performed by multiple clinicians (the inter-observer variability) was found to be minimal, with intraclass correlation coefficients (ICCs) ≥ 0.995. Lastly, we explored differences in fetal anthropometric growth trajectories, estimated with fractional polynomial mixed-effects prediction models, with increased maternal first trimester air pollution exposure, estimated by spatial interpolation models of exposure assessment. Increased maternal exposure to air pollution in the first trimester was negatively associated with the growth of fetal anthropometric parameters at various periods of gestation; point estimates of effect varied by air pollutant and fetal parameter. Reductions of fetal parameter growth trajectories associated with increased air pollution exposure lend support to the continued review and enforcement of existing air pollution standards, and efforts to reduce exposure to pollution, especially among vulnerable populations.