Risk of Congenital Heart Defects after Ambient Heat Exposure Early in Pregnancy

Abstract

Background: Congenital heart defects may be environmentally related, but the association with elevated ambient temperature has received little attention.

Objectives: We studied the relationship between outdoor heat during the first trimester of pregnancy and risk of congenital heart defects.

Methods: We carried out a retrospective cohort study of 704,209 fetuses between 2 and 8 weeks postconception from April to September in Quebec, Canada, 1988-2012. We calculated the prevalence of congenital heart defects at birth according to the number of days women were exposed to maximum temperature ≥ 30°C. In log-binomial regression models, we estimated prevalence ratios (PR) and 95% confidence intervals (CI) for the relationship of temperature with seven critical and eight noncritical heart defects, adjusted for pregnancy characteristics.

Results: Prevalence of congenital heart defects was 979.5 per 100,000 for 10 days or more of temperature ≥ 30°C compared with 878.9 per 100,000 for 0 days of exposure. Temperature was more precisely associated with noncritical than critical defects, which had lower prevalence. Fetuses exposed to 15 days of temperature ≥ 30°C between 2 and 8 weeks postconception had 1.06 times the risk of critical defects (95% CI: 0.67, 1.67) and 1.12 times the risk of noncritical defects (95% CI: 0.98, 1.29) relative to 0 days. Associations were higher for atrial septal defects (PR 1.37, 95% CI: 1.10, 1.70) than for other noncritical defects. For atrial septal defects, associations with elevated temperatures began the 3rd week postconception.

Conclusions: Extreme heat exposure during the first trimester may be associated with noncritical heart defects, especially of the atrial septum. Citation: Auger N, Fraser WD, Sauve R, Bilodeau-Bertrand M, Kosatsky T. 2017. Risk of congenital heart defects after ambient heat exposure early in pregnancy. Environ Health Perspect 125:8-14; http://dx.doi.org/10.1289/EHP171.

Figure 1

Association between ambient temperature 2–8 weeks postconception and congenital heart defects, Quebec, April through September, 1988–2012. Note: Prevalence ratio (bold central line) and 95% CI (light outer bands) for number of days with maximum temperature ≥ 30°C between weeks 2 and 8 postconception, relative to 0 days, adjusted for maternal age, comorbidity, parity, multiple birth, socioeconomic area deprivation, month and period of conception, and humidity.

Figure 2

Association between ambient temperature 2–8 weeks postconception and critical heart defects, Quebec, April through September, 1988–2012. Note: Prevalence ratio (bold central line) and 95% CI (light outer bands) for number of days with maximum temperature ≥ 30°C between weeks 2 and 8 postconception, relative to 0 days, adjusted for maternal age, comorbidity, parity, multiple birth, socioeconomic area deprivation, month and period of conception, and humidity.

Figure 3

Association between ambient temperature 2–8 weeks postconception and noncritical heart defects, Quebec, April through September, 1988–2012. Note: Prevalence ratio (bold central line) and 95% CI (light outer bands) for number of days with maximum temperature ≥ 30°C between weeks 2 and 8 postconception, relative to 0 days, adjusted for maternal age, comorbidity, parity, multiple birth, socioeconomic area deprivation, month and period of conception, and humidity.

Figure 4

Association between maximum weekly temperature 2–8 weeks postconception and congenital heart defects, Quebec, April through September, 1988–2012. Note: Prevalence ratio (bold central line) and 95% confidence interval (light outer bands) for maximum temperature during each week postconception, relative to 20°C, adjusted for maternal age, comorbidity, parity, multiple birth, socioeconomic area deprivation, month and period of conception, and humidity. Associations at weeks 3, 5, and 7 are not shown to conserve space, but reflect the same trend.