Stillbirths and complications from preterm birth are two of the leading causes of neonatal deaths across the globe. Lower- to middle-income countries (LMICs) are experiencing some of the highest rates of these adverse birth outcomes. Research has suggested that environmental determinants, such as extreme heat, can increase the risk of preterm birth and stillbirth. Under climate change, extreme heat events have become more severe and frequent and are occurring in differential seasonal patterns. Little is known about how extreme heat affects the risk of preterm birth and stillbirth in LMICs. Thus, it is imperative to examine how exposure to extreme heat affects adverse birth outcomes in regions with some of the highest rates of preterm and stillbirths. Most of the evidence linking extreme heat and adverse birth outcomes has been generated from high-income countries (HICs) notably because measuring temperature in LMICs has proven challenging due to the scarcity of ground monitors. The paucity of health data has been an additional obstacle to study this relationship in LMICs. In this study, globally gridded meteorological data was linked with spatially and temporally resolved Demographic and Health Surveys (DHS) data on adverse birth outcomes. A global analysis of 14 LMICs was conducted per a pooled time-stratified case-crossover design with distributed-lag nonlinear models to ascertain the relationship between acute exposure to extreme heat and PTB and stillbirths. We notably found that experiencing higher maximum temperatures and smaller diurnal temperature range during the last week before birth increased the risk of preterm birth and stillbirth. This study is the first global assessment of extreme heat events and adverse birth outcomes and builds the evidence base for LMICs.

死产和早产并发症是全球新生儿死亡的两个主要原因。中低收入国家 (LMIC) 正在经历这些不良出生结果的最高比率。研究表明，极端高温等环境决定因素会增加早产和死产的风险。在气候变化下，极端高温事件变得更加严重和频繁，并以不同的季节模式发生。关于极端高温如何影响中低收入国家早产和死产的风险知之甚少。因此，在一些早产和死产率最高的地区，有必要研究暴露于极端高温如何影响不良分娩结果。大多数将极端高温与不良出生结果联系起来的证据都来自高收入国家 (HIC)，特别是因为由于地面监测器的稀缺，在 LMIC 中测量温度已被证明具有挑战性。缺乏健康数据一直是研究中低收入国家这种关系的另一个障碍。在这项研究中，全球网格化的气象数据与空间和时间分辨的人口和健康调查 (DHS) 有关不良出生结果的数据相关联。对 14 个 LMICs 进行了全球分析，采用时间分层病例交叉设计和分布式滞后非线性模型，以确定急性暴露于极热与 PTB 和死产之间的关系。我们特别发现，在出生前的最后一周经历较高的最高温度和较小的昼夜温度范围会增加早产和死产的风险。这项研究是对极端高温事件和不良出生结局的首次全球评估，并为 LMICs 建立了证据基础。