The impact of extreme temperatures on birth outcomes in the Netherlands: a nationwide population-based study

BackgroundClimate projections predict an increased frequency and intensity of extreme weather events, such as extreme temperatures, prompting concerns about their impact on early-life health and health disparities. This study aimed to investigate the causal impact of in-utero exposure to extreme temperatures on birth outcomes and effect heterogeneity across levels of socioeconomic status (SES). MethodsWe obtained data on singleton births that occurred between 2003 and 2017 from the Dutch perinatal registry (N=2 472 352). Exposure was calculated as the number of days during the gestational period in which the mean temperature fell into each of mutually exclusive bins, with the 8-12 {degrees}C bin used as reference. To identify a causal effect, we exploited the unpredictability of daily temperature fluctuations while accounting for seasonal and underlying trends. Effect heterogeneity was assessed across levels of household income, neighbourhood SES, and maternal education. ResultsIn-utero exposure to an additional hot day (mean temperature > 20 {degrees}C), relative to the reference range, led to increased odds of low birth weight (LBW) (OR[95%CI]= 1.007 [1.005, 1.009]), small for gestational age (SGA) (OR[95%CI]= 1.004 [1.003, 1.005]), and preterm birth (PTB) (OR[95%CI]= 1.006 [1.005, 1.007]). Exposure during the second trimester to an additional cold day (< -4 {degrees}C) led to increased odds of LBW and PTB. The observed effects were the most detrimental for births in low-SES households. ConclusionsIn-utero exposure to extreme temperature has a detrimental impact on birth outcomes in the Netherlands. Projected increases in extreme temperatures may further exacerbate health disparities in early life.