Associations between fine particulate matter, extreme heat events and congenital heart defects
Previous research report associations between prenatal air pollution and the occurrence of congenital heart defects (CHD) in offspring. Extreme heat events (EHE) may modify the effect of air pollution on CHD risk during pregnancy. The objective of this research was to estimate the joint effect of exposure to fine particulate matter (PM2.5) and EHE during pregnancy on CHD occurrence.
Using data from the National Birth Defects Prevention Study, a large, multi-site population-based case-control study, exposure to PM2.5 and EHEs were assigned using the monitors closest to the maternal residential location in early pregnancy for each of the 4074 controls and 2632 CHD cases. Daily PM2.5 data from the closest monitor reporting to the Environmental Protection Agency’s Air Quality System, was averaged across weeks 3-8 post-conception. Using maximum ambient temperature data from the closest monitor reporting to the National Center for Atmospheric Research, the presence of an EHE was defined as ambient temperature in the upper 95th centile for at least two consecutive days. Interaction between PM2.5 exposure and EHE was assessed on both the multiplicative and additive scales using logistic regression models adjusted for maternal age, ethnicity, education and average humidity. Relative excess risks due to interaction (RERI) were calculated.
There was some evidence of a stronger relationship between PM2.5 and ventricular septal defects among women who experienced an EHE (odds ratio 2.14 95% confidence interval 1.19, 3.38); however the opposite was observed for right ventricular outflow tract obstructions and conotruncal defects. There is some suggestion that these relationships are stronger among women whose early pregnancies occur during the warmer seasons and in warmer climate regions of the United States.
This study did not provide substantial evidence of interaction between prenatal exposure to EHEs and PM2.5 and CHD occurrence in offspring.