Hira Fatima Syed, Khaliq Asif, Meherali Salima, Memon Zahid, Lassi Zohra S
Global Ecology, Partuyarta Ngadluku Wardli Kuu, College of Science and Engineering, Flinders University, Adelaide, SA, Australia.
College of Medicine and Public Health, Flinders University, Adelaide, SA, Australia.
Womens Health (Lond). 2025 Jan-Dec;21:17455057251341723. doi: 10.1177/17455057251341723. Epub 2025 Jun 5.
Exposure to extreme ambient temperatures during pregnancy, including both heat and cold, can lead to complications such as preterm births, low birth weight (LBW), and developmental anomalies. These exposures pose immediate health risks to both mother and child and may exacerbate health disparities across future generations.
Pakistan, with limited health resources, is particularly vulnerable to the impacts of extreme temperatures. This study aimed to quantify the association between heat and cold exposure and LBW in Pakistan.
Space-time-series study design.
We analysed 17,077 birth records from 10 datasets from the Multi-Indicator Cluster Surveys and 1 from the Pakistan Demographic and Health Surveys, covering monthly LBW cases from January 2008 to December 2017. These data were linked to monthly heat index estimates, derived from temperature and humidity, from Copernicus ERA5-Land, aggregated at the provincial level. We used a space-time-series study design with quasi-Poisson distributed lag nonlinear regression. Models were adjusted for long-term trends, seasonality, and socio-economic factors, including maternal education, wealth index and rural residence. We estimated the cumulative risk of LBW associated with heat and cold, individual lag effects and the attributable fraction of LBW cases due to temperature exposure.
LBW was reported in 26.02% ( = 4444) of total birth records. The overall exposure-response relationship indicated a positive association between LBW and extreme heat; however, the estimates were imprecise and included the null. At lag 0 (month of conception), there was evidence of increased risk during periods of moderate heat (90th percentile: relative risk (RR) 1.70; 95% confidence interval (CI): 1.01, 2.87) and extreme heat (99th percentile: RR 1.93; 95% CI: 1.00, 3.71). The heat-related attributable fraction for LBW ranged from 0.34 to 0.42 across provinces. In contrast, no association was found between LBW and cold exposure.
This study contributes to the existing body of evidence of the association between extreme temperatures and LBW, particularly from a low-resource, highly vulnerable country. Notably, we found a positive association between heat exposure and LBW during the first month of pregnancy (lag 0), suggesting that early gestation may be a critical period of vulnerability.
孕期暴露于极端环境温度，包括高温和低温，可导致早产、低出生体重（LBW）和发育异常等并发症。这些暴露对母婴均构成直接健康风险，并可能加剧未来几代人的健康差距。
巴基斯坦卫生资源有限，特别容易受到极端温度的影响。本研究旨在量化巴基斯坦高温和低温暴露与低出生体重之间的关联。
时空序列研究设计。
我们分析了来自多指标类集调查的10个数据集和巴基斯坦人口与健康调查的1个数据集中的17,077份出生记录，涵盖2008年1月至2017年12月的每月低出生体重病例。这些数据与根据哥白尼ERA5-Land的温度和湿度得出的省级汇总月度热指数估计值相关联。我们采用时空序列研究设计，使用准泊松分布滞后非线性回归。模型针对长期趋势、季节性和社会经济因素进行了调整，包括母亲教育程度、财富指数和农村居住情况。我们估计了与高温和低温相关的低出生体重累积风险、个体滞后效应以及因温度暴露导致的低出生体重病例归因比例。
在所有出生记录中，26.02%（n = 4444）报告为低出生体重。总体暴露 - 反应关系表明低出生体重与极端高温之间存在正相关；然而，估计值不准确且包括零值。在滞后0（受孕月份），有证据表明在中度高温时期（第90百分位数：相对风险（RR）1.70；95%置信区间（CI）：1.01，2.87）和极端高温时期（第99百分位数：RR 1.93；95% CI：1.00，3.71）风险增加。各省份因高温导致的低出生体重归因比例在0.34至0.42之间。相比之下，未发现低出生体重与低温暴露之间存在关联。
本研究为极端温度与低出生体重之间关联的现有证据做出了贡献，特别是来自资源匮乏、高度脆弱国家的证据。值得注意的是，我们发现怀孕第一个月（滞后0）高温暴露与低出生体重之间存在正相关，这表明妊娠早期可能是一个关键的脆弱期。
