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

Abstract

Links between heat exposure and congenital anomalies have not been explored in detail despite animal data and other strands of evidence that indicate such links are likely. We reviewed articles on heat and congenital anomalies from PubMed and Web of Science, screening 14,880 titles and abstracts in duplicate for articles on environmental heat exposure during pregnancy and congenital anomalies. Thirteen studies were included. Most studies were in North America (8) or the Middle East (3). Methodological diversity was considerable, including in temperature measurement, gestational windows of exposure, and range of defects studied. Associations were detected between heat exposure and congenital cardiac anomalies in three of six studies, with point estimates highest for atrial septal defects. Two studies with null findings used self-reported temperature exposures. Hypospadias, congenital cataracts, renal agenesis/hypoplasia, spina bifida, and craniofacial defects were also linked with heat exposure. Effects generally increased with duration and intensity of heat exposure. However, some neural tube defects, gastroschisis, anopthalmia/microphthalmia and congenital hypothyroidism were less frequent at higher temperatures. While findings are heterogenous, the evidence raises important concerns about heat exposure and birth defects. Some heterogeneity may be explained by biases in reproductive epidemiology. Pooled analyses of heat impacts using registers of congenital anomalies are a high priority.

Effect of Elevated Ambient Temperature on Maternal, Foetal, and Neonatal Outcomes: A Scoping Review

“…Available evidence suggests that elevated temperature increases some types of congenital anomalies, such as congenital heart defects and neural tube defects [14,42,47,48]. Consistent with the recent systematic review findings on the effects of high temperatures on congenital anomalies [98], our scoping review also observed that the evidence was strongest for congenital heart defects. However, the susceptible exposure window period for congenital anomalies was less clear.…”

“…Furthermore, this scoping review found that the current knowledge of temperaturerelated adverse maternal, foetal, and neonatal effects is dominated by findings from the USA, China, Canada, and some European countries. Additionally, consistent with other systematic reviews [98,100], minimal studies were conducted in lower-middle-income countries and low-income countries. Therefore, we do not know the effect of heat on adverse pregnancy and birth outcomes in low-income countries.…”

“…However, the susceptible exposure window period for congenital anomalies was less clear. Still, most studies (5 out of 6 studies) investigated the impact of heat on the first few weeks of pregnancy because the first trimester of pregnancy was considered the critical period of organogenesis [98]. However, due to the methodological diversity and the limited number of studies on each type of congenital anomaly, further research is required to conclude exposure relationships and susceptible windows for heat-associated congenital anomalies.…”

“…To date, only one meta-analysis was conducted on this topic, focusing on the high-temperature associations on PTB, LBW, and stillbirth, and found that evidence was most consistent and effect size largest for PTB and stillbirths [20]. In addition, two systematic reviews were conducted on GDM [97] and congenital anomalies [98] recently.Consistently with our scoping review, both of these systematic reviews highlighted that the low number of studies, statistical heterogeneity, and methodological diversity limits the possibility of conducting a meta-analysis to quantify the connection between temperature and the outcomes examined. Similarly, pooling the results of other outcomes mentioned in this scoping review is not feasible due to the considerable variation in study designs, sample size, temperature metrics, exposure windows, and heatwave definitions used to estimate the effect size: another gap identified in this review.…”

The importance of body core temperature evaluation in balneotherapy

“…Adopting such an approach ensures that each characteristic of the patient is taken into consideration when planning treatment. BCT monitoring is important in order to prevent and reduce the risks that may occur due to heat applications in certain conditions such as pregnancy, pediatric ages, diseases affecting thermoregulatory autonomic pathways, and drug use (Leyk et al 2019;Vaidyanathan et al 2020;Haghighi et al 2021). Current balneotherapy practices involve uncertainties, for example, how to manage adverse effects from heat in pregnant patients.…”