The effect of prenatal temperature and PM2.5 exposure on birthweight: weekly windows of exposure throughout the pregnancy

Abstract

BACKGROUND AND AIM: Birthweight is a strong predictor of normal growth, healthy development, and survival. Several studies have found associations between temperature, fine particulate matter (PM2.5), and birth weight. However, the relevant timing of exposures varies between studies and is yet unclear. Therefore, we assessed the difference in term birthweight (TBW) associated with weekly exposure to temperature and PM2.5 throughout 37 weeks of gestation. METHODS: We included all singleton live term births in Massachusetts, U.S between 2004 and 2015 (n=712,438). Weekly PM2.5 and temperature predictions were estimated on a 1 km grid from satellite-based models. We utilized a distributed lag nonlinear model (DLNM) to estimate the difference in TBW associated with weekly exposures to PM2.5 and temperature simultaneously from the last menstrual period to 37 weeks of gestation. RESULTS:We found a nonlinear association with temperature exposure. We observed positive differences in TBW associated with rises of colder temperatures (2.6g increase, 95% CI 0.1g; 5.1g, for one ºC increase from -4 ºC) and negative difference in TBW associated with rises of warmer temperatures (7.9g decrease, 95% CI -11.2g; -4.6g, for one ºC increase from 23 ºC). Temperature effects were larger in the first and final weeks of gestation. We observed a negative difference in TBW associated with PM2.5 exposure. Overall, one µg/m3 increase in prenatal exposure was associated with 3.9g lower TBW (95% CI -5.0g; -2.9g). PM2.5 effects were larger in the final weeks of gestation. CONCLUSIONS:We found heat and PM2.5 exposure to be related to lower TBW. Our findings suggest that women are more susceptible to both exposures towards the end of pregnancy. Susceptibility to heat was higher in the initial weeks of pregnancy as well. These critical windows of susceptibility can be communicated to pregnant women during routine prenatal visits to increase awareness and target interventions to reduce exposures. KEYWORDS: birthweight, temperature, air pollution, birth outcomes