A population‐based case–control study of the association between weather‐related extreme heat events and orofacial clefts

Abstract

Background Limited epidemiologic research exists on the association between weather‐related extreme heat events (EHEs) and orofacial clefts (OFCs). We estimated the associations between maternal exposure to EHEs in the summer season and OFCs in offspring and investigated the potential modifying effect of body mass index on these associations. Methods We conducted a population‐based case–control study among mothers who participated in the National Birth Defects Prevention Study for whom at least 1 day of their first two post‐conception months occurred during summer. Cases were live‐born infants, stillbirths, and induced terminations with OFCs; controls were live‐born infants without major birth defects. We defined EHEs using the 95th and the 90th percentiles of the daily maximum universal apparent temperature distribution. We used unconditional logistic regression with Firth's penalized likelihood method to estimate adjusted odds ratios and 95% confidence intervals, controlling for maternal sociodemographic and anthropometric variables. Results We observed no association between maternal exposure to EHEs and OFCs overall, although prolonged duration of EHEs may increase the risk of OFCs in some study sites located in the Southeast climate region. Analyses by subtypes of OFCs revealed no associations with EHEs. Modifying effect by BMI was not observed. Conclusions We did not find a significantly increased risk of OFCs associated with maternal exposure to EHEs during the relevant window of embryogenesis. Future studies should account for maternal indoor and outdoor activities and for characteristics such as hydration and use of air conditioning that could modify the effect of EHEs on pregnant women.

Impacts of High Environmental Temperatures on Congenital Anomalies: A Systematic Review

“…The search in the mapping review identified 14,880 articles after removal of duplicate records ( Figure 1 ). Overall, 2273 articles were classified as “heat-exposure studies or heat adaptation studies”, and 175 of these were selected for full text screening, with 13 eligible for this review [ 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ]. A meta-analysis was not conducted due to considerable methodological diversity, statistical heterogeneity and the limited number of studies on each congenital defect.…”

“…The studies were published between 1991 and 2018 and covered births that took place in the period 1982 to 2015. In total, six studies reported on cardiac defects [ 22 , 25 , 28 , 30 , 32 , 33 ], three on neural tube defects [ 24 , 31 , 33 ], two on orofacial cleft or cranial defects [ 33 , 34 ], two on hypothyroidism [ 23 , 27 ], and one each on ocular anomalies [ 33 ], renal anomaly [ 33 ], hypospadias [ 29 ], musculoskeletal defects [ 33 ] and any lethal anomaly [ 26 ]. One paper covered multiple outcomes covering six organ systems [ 33 ].…”

“…In a sub-analysis stratified by ethnic group, however, cleft lip with or without cleft palate was 3.02 fold more common among the Hispanic population after heatwave exposure (95% CI = 1.44, 6.33), while no associations were noted in non-Hispanic groups [ 33 ]. A study in eight US states involving 907 cases reported null findings, with point estimates ranging from 0.45 to 1.43, and no discernable patterns in the findings [ 34 ].…”

A population-based case–control study of the association between weather-related extreme heat events and low birthweight

“…However, in the instance where maternal due date was not available, then date of last menstrual period was used by adding 14 d to date of last menses. 16 Birth records were merged with daily weather data, and three exposure indicators were developed: EHE (yes/no), EHE duration, and EHE frequency. We used two definitions for EHE to determine duration and severity: 1) at least three consecutive days with maximum temperature ≥32.2°C/90°F (EHE90), and 2) two consecutive days of temperature ≥97th percentile of the distribution of the maximum temperature for the summer season (EHE97).…”

“…We used two definitions for EHE to determine duration and severity: 1) at least three consecutive days with maximum temperature ≥32.2°C/90°F (EHE90), and 2) two consecutive days of temperature ≥97th percentile of the distribution of the maximum temperature for the summer season (EHE97). 16 Exposure to EHE90 or EHE97 was defined as exposed.…”