Medical Research Council Unit The Gambia at London School of Hygiene and Tropical Medicine, Fajara, The Gambia.
Centre on Climate Change and Planetary Health, London School of Hygiene and Tropical Medicine, London, UK.
BJOG. 2024 Apr;131(5):623-631. doi: 10.1111/1471-0528.17622. Epub 2023 Jul 28.
Exposure to extreme heat in pregnancy increases the risk of stillbirth. Progress in reducing stillbirth rates has stalled, and populations are increasingly exposed to high temperatures and climate events that may further undermine health strategies. This narrative review summarises the current clinical and epidemiological evidence of the impact of maternal heat exposure on stillbirth risk. Out of 20 studies, 19 found an association between heat and stillbirth risk. Recent studies based in low- to middle-income countries and tropical settings add to the existing literature to demonstrate that all populations are at risk. Additionally, both short-term heat exposure and whole-pregnancy heat exposure increase the risk of stillbirth. A definitive threshold of effect has not been identified, as most studies define exposure as above the 90th centile of the usual temperature for that population. Therefore, the association between heat and stillbirth has been found with exposures from as low as >12.64°C up to >46.4°C. The pathophysiological pathways by which maternal heat exposure may lead to stillbirth, based on human and animal studies, include both placental and embryonic or fetal impacts. Although evidence gaps remain and further research is needed to characterise these mechanistic pathways in more detail, preliminary evidence suggests epigenetic changes, alteration in imprinted genes, congenital abnormalities, reduction in placental blood flow, size and function all play a part. Finally, we explore this topic from a public health perspective; we discuss and evaluate the current public health guidance on minimising the risk of extreme heat in the community. There is limited pregnancy-specific guidance within heatwave planning, and no evidence-based interventions have been established to prevent poor pregnancy outcomes. We highlight priority research questions to move forward in the field and specifically note the urgent need for evidence-based interventions that are sustainable.
孕期暴露于极端高温会增加胎儿死亡的风险。降低胎儿死亡率的进展已经停滞不前，而人群越来越多地暴露在高温和气候事件中，这可能会进一步破坏健康策略。本叙述性综述总结了目前关于母体热暴露对胎儿死亡风险影响的临床和流行病学证据。在 20 项研究中，有 19 项发现热暴露与胎儿死亡风险之间存在关联。最近在中低收入国家和热带地区进行的研究增加了现有文献，证明所有人群都有风险。此外，短期热暴露和整个孕期热暴露都会增加胎儿死亡的风险。由于大多数研究将暴露定义为高于该人群通常温度的第 90 百分位数，因此尚未确定明确的效应阈值。因此，已经发现热与胎儿死亡之间的关联与暴露程度有关，从低至>12.64°C 到高至>46.4°C。基于人体和动物研究，母体热暴露可能导致胎儿死亡的病理生理途径包括胎盘和胚胎或胎儿的影响。尽管仍然存在证据差距，并且需要进一步研究来更详细地描述这些机制途径，但初步证据表明，表观遗传变化、印记基因改变、先天性异常、胎盘血流量减少、大小和功能降低都起作用。最后，我们从公共卫生的角度探讨这个话题；我们讨论并评估了目前关于在社区中尽量减少极端高温风险的公共卫生指南。在热浪规划中，针对妊娠的具体指导有限，并且尚未建立预防不良妊娠结局的基于证据的干预措施。我们强调了该领域的优先研究问题，并特别指出需要基于证据的、可持续的干预措施。
