Auger Nathalie, Naimi Ashley I, Smargiassi Audrey, Lo Ernest, Kosatsky Tom
From the aInstitut national de santé publique du Québec, Montreal, Quebec, Canada; bResearch Centre of the University of Montreal Hospital Centre, Montreal, Quebec, Canada; cDepartment of Epidemiology, Biostatistics and Occupational Health, McGill University, Montreal, Quebec, Canada; dDepartment of Environmental and Occupational Health, University of Montreal, Quebec, Canada; and eBritish Columbia Centre for Disease Control, Vancouver, British Columbia, Canada.
Epidemiology. 2014 May;25(3):344-50. doi: 10.1097/EDE.0000000000000074.
The relationship between ambient temperature and risk of delivery is poorly understood. We examined the association between heat and risk of delivery among preterm and term pregnancies with the use of a time-to-event design to minimize bias from seasonal variation in conception rates.
We used data on 206,929 term and 12,390 preterm singleton live births for Montreal, Canada, from June through September, 1981-2010. The exposure variables were (1) maximum daily temperatures in the week preceding birth and (2) number of consecutive days with temperatures of 32°C or above during the preceding week. We estimated hazards of delivery among preterm (<37 gestational weeks), early-term (37-38 weeks), and full-term (≥39 weeks) pregnancies for both exposures in Cox regression models, adjusting for maternal characteristics. Sensitivity analyses were carried out adjusting for markers of air pollution.
Maximum temperatures reached at least 32°C during the preceding week for 19,829 births (9.0%). Relative to a maximum of 20°C, the hazard of delivery within term was 4% higher for maximum temperatures of 32°C or higher, but no association was found for preterm delivery. Associations were stronger with early-term than with full-term delivery. Extreme heat episodes with 4 to 7 days of maximum temperature of at least 32°C were associated with a 27% greater hazard of delivery among early-term pregnancies relative to other days.
High ambient temperature and extreme heat episodes may trigger earlier delivery among term births.
环境温度与分娩风险之间的关系尚不清楚。我们采用事件发生时间设计，以尽量减少受孕率季节性变化带来的偏倚，研究了高温与早产和足月妊娠分娩风险之间的关联。
我们使用了1981年至2010年6月至9月加拿大蒙特利尔市206,929例足月单胎活产和12,390例早产单胎活产的数据。暴露变量为：（1）出生前一周的每日最高气温；（2）前一周内气温达到32°C及以上的连续天数。我们在Cox回归模型中估计了早产（孕周<37周）、早期足月产（37-38周）和足月产（孕周≥39周）妊娠中两种暴露情况下的分娩风险，并对产妇特征进行了调整。还进行了敏感性分析，对空气污染指标进行了调整。
19,829例分娩（9.0%）的前一周最高气温至少达到32°C。相对于最高气温20°C，最高气温达到32°C及以上时，足月分娩风险高出4%，但未发现与早产有相关性。早期足月产的相关性比足月产更强。最高气温至少为32°C持续4至7天的极端高温事件与早期足月产妊娠的分娩风险比其他日子高27%相关。
高环境温度和极端高温事件可能会引发足月分娩提前。
