Background

Extreme temperatures may lead to adverse pregnancy and birth outcomes, including low birthweight. Studies on the impact of temperature on birthweight have been inconclusive due to methodological challenges related to operationalizing temperature exposure, the definitions of exposure windows, accounting for gestational age, and a limited geographic scope.

Methods

We combined data on individual-level term live births (N≈15 million births) from urban areas in Brazil, Chile, and Mexico from 2010 to 2015 from the SALURBAL study (Urban Health in Latin America) with high-resolution daily air temperature data and computed average ambient temperature for every month of gestation for each newborn. Associations between full-term birthweight and average temperature during gestation were analyzed using multi-level distributed lag non-linear models that adjusted for newborn’s sex, season of conception, and calendar year of child’s birth; controlled for maternal age, education, partnership status, presence of previous births, and climate zone; and included a random term for the sub-city of mother’s residence.

Findings

Higher temperatures during the entire gestation are associated with lower birthweight, particularly in Mexico and Brazil. The cumulative effect of temperature on birthweight is mostly driven by exposure to higher temperatures during months 7–9 of gestation. Higher maternal education can attenuate the temperature-birthweight associations.

Interpretation

Our work shows that climate-health impacts are likely to be context- and place-specific and warrants research on temperature and birthweight in diverse climates to adequately anticipate global climate change. Given the high societal cost of suboptimal birthweight, public health efforts should be aimed at diminishing the detrimental effect of higher temperatures on birthweight.

Funding

The Wellcome Trust.

中文翻译：

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拉丁美洲城市的环境温度和足月出生体重

背景

极端温度可能导致不良妊娠和分娩结果，包括低出生体重。由于与操作温度暴露、暴露窗口的定义、考虑胎龄和有限的地理范围相关的方法学挑战，关于温度对出生体重影响的研究尚无定论。

方法

我们将来自 SALURBAL 研究（拉丁美洲的城市健康）的 2010 年至 2015 年巴西、智利和墨西哥城市地区的个体水平足月活产（N≈1500 万新生儿）数据与高分辨率的每日气温数据相结合并计算每个新生儿每个月的平均环境温度。使用针对新生儿性别、受孕季节和孩子出生日历年进行调整的多层次分布滞后非线性模型分析了足月出生体重与妊娠期平均体温之间的关联；受孕产妇年龄、教育程度、伴侣状况、是否有过生育和气候区的控制；并包括一个随机术语，用于母亲居住的子城市。

发现

整个妊娠期间较高的温度与较低的出生体重有关，尤其是在墨西哥和巴西。温度对出生体重的累积影响主要是由于在妊娠 7-9 个月内暴露于较高的温度。较高的孕产妇教育可以减弱体温-出生体重的关联。

解释

我们的工作表明，气候健康影响可能因环境和地点而异，因此需要对不同气候下的温度和出生体重进行研究，以充分预测全球气候变化。鉴于次优出生体重的高社会成本，公共卫生工作应旨在减少高温对出生体重的不利影响。

资金

威康信托。