Projected Changes in Maternal Heat Exposure During Early Pregnancy and the Associated Congenital Heart Defect Burden in the United States

Abstract

Background More intense and longer‐lasting heat events are expected in the United States as a consequence of climate change. This study aimed to project the potential changes in maternal heat exposure during early pregnancy (3–8 weeks post conception) and the associated burden of congenital heart defects ( CHD s) in the future. Methods and Results This study expanded on a prior nationwide case‐control study that evaluated the association between CHD s and maternal heat exposure during early pregnancy in summer and spring. We defined multiple indicators of heat exposure, and applied published odds ratios obtained for the matching season of the baseline (1995–2005) into the projection period (2025–2035) to estimate potential changes in CHD burden throughout the United States. Increases in maternal heat exposure were projected across the United States and to be larger in the summer. The Midwest will potentially have the highest increase in summer maternal exposure to excessively hot days (3.42; 95% CI, 2.99–3.88 per pregnancy), heat event frequency (0.52; 95% CI, 0.44–0.60) and heat event duration (1.73; 95% CI, 1.49–1.97). We also found large increases in specific CHD subtypes during spring, including a 34.0% (95% CI, 4.9%–70.8%) increase in conotruncal CHD in the South and a 38.6% (95% CI , 9.9%–75.1%) increase in atrial septal defect in the Northeast. Conclusions Projected increases in maternal heat exposure could result in an increased CHD burden in certain seasons and regions of the United States.

Taking the Heat: Potential Fetal Health Effects of Hot Temperatures

“…Several epidemiological studies over the past five years have reported associations between high temperatures and adverse pregnancy outcomes, including preterm birth, stillbirth, and low birth weight (LBW),3 , 4 as well as congenital heart defects 5. (At least two studies have also examined ambient temperature in relation to neural tube defects 6 , 7…”

“…Animal studies suggest that heat exposure during early pregnancy could interfere with normal protein synthesis through the production of heat-shock proteins 11. Disrupting protein homeostasis could lead to fetal cell damage, potentially altering fetal development 5. Previous research in the general (nonpregnant) population shows that circulating levels of markers of inflammation and oxidative stress are associated with ambient temperatures 12 , 13 , 14 , 15.…”

A Comprehensive Assessment of the Associations Between Season of Conception and Birth Defects, Texas, 1999–2015

“…Using a stringent analytic approach, 5% of birth defects were associated with season of conception. Because previous studies have focused on more common birth defects, such as cleft lip and palate, cardiac anomalies, and neural tube defects (NTDs), scant data are available for many anomalies [ 12 , 19 , 20 , 21 ]. Our findings provide evidence of increased prevalence of several such birth defects among offspring conceived in the summer relative to the winter.…”

“…High temperatures can increase ozone concentrations and trap pollutants closer to the ground [ 26 ]. Animal studies indicate that maternal heat exposure during early pregnancy may induce fetal cell death or malformations [ 19 , 27 ]. In support of this, Lin et al found increased odds of congenital heart disease for offspring of women who experienced more frequent or longer lasting extreme heat events during the spring or summer [ 20 ].…”

A predictive model of offspring congenital heart disease based on maternal risk factors during pregnancy: a hospital based case-control study in Nanchong City

“…Substantial epidemiological evidence associates the sustained presence of adverse healthy lifestyle factors with increased risk of CHD mortality 4 . However, few studies have been done to predict the risk of individual congenital malformations, including CHD 5 .…”