Heatwaves are becoming more frequent and may acutely increase the risk of stillbirth, a rare and severe pregnancy outcome. Examine the association between multiple heatwave metrics and stillbirth in six U.S. states. Data were collected from fetal death and birth records in California (1996–2017), Florida (1991–2017), Georgia (1994–2017), Kansas (1991–2017), New Jersey (1991–2015), and Oregon (1991–2017). Cases were matched to controls 1:4 based on maternal race/ethnicity, maternal education, and county, and exposure windows were aligned (gestational week prior to stillbirth). County-level temperature data were obtained from Daymet and linked to cases and controls by residential county and the exposure window. Five heatwave metrics (1 categorical, 3 dichotomous, 1 continuous) were created using different combinations of the duration and intensity of hot days (mean daily temperature exceeding the county-specific 97.5th percentile) during the exposure window, as well as a continuous measure of mean temperature during the exposure window modeled using natural splines to allow for nonlinear associations. State-specific odds ratios (ORs) and 95% confidence intervals (CI) were estimated using conditional logistic regression models. State-specific results were pooled using a fixed-effects meta-analysis. In our data set of 140,428 stillbirths (553,928 live birth controls), three of the five heatwave metrics examined were not associated with stillbirth. However, four consecutive hot days during the previous week was associated with a 3% increase in stillbirth risk (CI: 1.01, 1.06), and a 1 °C average increase over the threshold was associated with a 10% increase in stillbirth risk (CI: 1.04, 1.17). In continuous temperature analyses, there was a slight increased risk of stillbirth associated with extremely hot temperatures (≥ 35 °C). Most heat wave definitions examined were not associated with acute changes in stillbirth risk; however, the most extreme heatwave durations and temperatures were associated with a modest increase in stillbirth risk.

中文翻译：

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美国六个州的热浪与死产之间存在密切关联


热浪变得越来越频繁，可能会急剧增加死产的风险，死产是一种罕见且严重的妊娠结局。检查美国六个州的多个热浪指标与死产之间的关联。数据收集自加利福尼亚州（1996-2017年）、佛罗里达州（1991-2017年）、佐治亚州（1994-2017年）、堪萨斯州（1991-2017年）、新泽西州（1991-2015年）和俄勒冈州（1991年）的胎儿死亡和出生记录–2017）。根据母亲种族/民族、母亲教育程度和县，将病例与对照进行 1:4 匹配，并调整暴露窗口（死产前的孕周）。县级温度数据从 Daymet 获得，并与居住县和暴露窗口的病例和对照相关联。使用暴露窗口期间炎热天气的持续时间和强度（平均每日温度超过县特定 97.5%）的不同组合以及连续测量，创建了五个热浪指标（1 个分类指标、3 个二分指标、1 个连续指标）使用自然样条建模的暴露窗口期间的平均温度，以允许非线性关联。使用条件逻辑回归模型估计州特定优势比 (OR) 和 95% 置信区间 (CI)。使用固定效应荟萃分析汇总各州的具体结果。在我们的 140,428 例死产（553,928 例活产控制）数据集中，检查的五个热浪指标中有 3 个与死产无关。然而，上周连续四天高温与死产风险增加 3% 相关（CI：1.01，1.06），超过阈值平均升高 1 °C 与死产风险增加 10% 相关（CI：1.01，1.06）。 ：1.04、1.17）。 在连续温度分析中，与极热温度（≥ 35 °C）相关的死产风险略有增加。大多数研究的热浪定义与死产风险的急剧变化无关；然而，最极端的热浪持续时间和温度与死产风险的适度增加有关。