BACKGROUND/OBJECTIVE Few studies have assessed the effect of ambient heat during the fetal development period on congenital heart defects (CHDs), especially in transitional seasons. We examined and compared the associations between extreme heat and CHD phenotypes in summer and spring, assessed their geographical differences, and compared different heat indicators. METHODS We identified 5848 CHD cases and 5742 controls (without major structural defects) from the National Birth Defects Prevention Study, a US multicenter, population-based case-control study. Extreme heat events (EHEs) were defined by using the 95th (EHE95) or 90th (EHE90) percentile of daily maximum temperature and its frequency and duration during postconceptional weeks 3-8. We used a two-stage Bayesian hierarchical model to examine both regional and study-wide associations. Exposure odds ratios (ORs) were calculated using multivariate logistic regression analyses, while controlling for potential confounding factors. RESULTS Overall, we observed no significant relationships between maternal EHE exposure and CHDs in most regions during summer. However, we found that 3-11 days of EHE90 during summer and spring was significantly associated with ventricular septal defects (VSDs) study-wide (ORs ranged: 2.17-3.24). EHE95 in spring was significantly associated with conotruncal defects and VSDs in the South (ORs: 1.23-1.78). Most EHE indicators in spring were significantly associated with increased septal defects (both VSDs and atrial septal defects (ASDs)) in the Northeast. CONCLUSION While generally null results were found, long duration of unseasonable heat was associated with the increased risks for VSDs and ASDs, mainly in South and Northeast of the US. Further research to confirm our findings is needed.

中文翻译：

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夏季和春季早孕期间孕妇的环境热量暴露以及先天性心脏缺陷-一项基于美国人口的大型病例对照研究。

背景/目的很少有研究评估胎儿发育期间环境热量对先天性心脏缺陷（CHD）的影响，尤其是在过渡季节。我们检查并比较了夏季和春季极端热量与冠心病表型之间的关联，评估了它们的地理差异，并比较了不同的热量指标。方法我们从美国多中心，基于人群的病例对照研究《国家出生缺陷预防研究》中鉴定出5848例CHD病例和5742例对照（无重大结构缺陷）。极端热事件（EHE）的定义是在受孕后第3-8周使用每日最高温度的第95个（EHE95）或第90个（EHE90）百分数以及其频率和持续时间。我们使用了两阶段贝叶斯分层模型来检查区域和研究范围的关联。使用多元逻辑回归分析计算暴露比值比（OR），同时控制潜在的混杂因素。结果总体而言，我们观察到夏季大多数地区的孕妇EHE暴露与冠心病之间无显着相关性。但是，我们发现在整个夏季和春季，EHE90的3-11天与室间隔缺损（VSD）显着相关（OR范围为2.17-3.24）。春季的EHE95与南方的圆锥体轮缺损和VSD显着相关（OR：1.23-1.78）。春季大多数EHE指标与东北地区的间隔缺损增加（VSD和房间隔缺损（ASD））显着相关。结论虽然通常没有发现任何结果，但长期不合时宜的热量会增加VSD和ASD的风险，主要在美国南部和东北部。需要进一步的研究以确认我们的发现。