The Exposure Science Aspects of the Re-Envisioning of the (U.S.) National Library of Medicine's Toxicology and Environmental Health Resources

Abstract

Background/Objective: High ambient temperature is shown to influence birth outcomes, however, few studies have assessed heat’s effect during the fetal development period on congenital heart defects (CHDs), especially in transitional seasons. We examined and compared the associations between extreme heat and CHD phenotypes in summer and spring, assessed their geographical differences, and compared different heat indicators.Methods: We identified all 5,848 CHD cases and 5,742 controls (without major structural defects) from the National Birth Defects Prevention Study, a United States (U.S.) multicenter population-based case-control study. Extreme heat events (EHEs) were defined by using 95th (EHE95) or 90th (EHE90) percentile of daily maximum temperature and its frequency and duration during postconceptional weeks 3-8. We used a two-stage Bayesian hierarchical model to examine both regional and study-wide associations. Exposure odds ratios (ORs) were calculated using multivariate logistic regression analyses, while controlling for potential confounding factors.Results: Overall, we observed no consistent relationships between maternal EHE exposure and CHDs in most regions. However, we found that 3-11 days of EHE90 in both summer and spring was significantly associated with ventricular septal defects (VSDs) study-wide (ORs ranged: 2.17-3.24). EHE95 in spring were significantly associated with conotruncal defects and VSDs in the South (ORs: 1.23-1.78). Most EHE indicators in spring were significantly associated with increased septal defects (VSDs and atrial septal defects (ASDs)) in the Northeast.Conclusion: While generally null results were found, longer heat durations were associated with increased risks for VSDs and ASDs, mainly in the South and Northeastern U.S., as well as transitional months in spring when using multiple heat indicators. Further research is needed to confirm our findings.