Associations between prenatal exposure to ambient temperature and birthweight small-for-gestational-age: an...

Previous studies on prenatal ambient temperature and birth weight revealed significant associations, with the direction of the effect varying across studies. However, they excluded preterm births and were limited in examining critical windows of exposure. We addressed these limitations by analyzing ~130,000 term and preterm births at Soroka Hospital in Southern Israel (2004-2019). Weekly temperature exposure was estimated based on maternal residence, using a spatiotemporal model, and its association with Small for Gestational Age (SGA, birth weight < 10^th percentile) was assessed. We conducted a two-stage analysis: (1) stratifying the cohort by gestation length and using distributed lag models to estimate temperature-SGA associations across pregnancy weeks, and (2) integrating these results into a weighted mean estimate. Overall, higher temperatures were weakly associated with a lower risk of SGA, with significant associations starting from the third trimester, reaching 0.93 (95% CI: 0.88-0.98) and 1.08 (95% CI: 1.01-1.16) for exposure to 38°C and 2°C, respectively, at 40 weeks, particularly in the Arab sub-population. In early preterm births, mid-pregnancy exposure to higher temperatures was strongly linked to increased SGA risk. The association varies across gestation lengths, with distinct critical windows, which underscore the importance of preterm inclusion when studying prenatal exposure and birth outcomes.