HIGH Horizons - Long term heat exposure during pregnancy and effects on perinatal health: Data analysis protocol, codes and R scripts

The data analysis protocol and scripts are supporting documents to repeat the analysis of the effects of heat exposure during pregnancy on perinatal health for any other country, following the same harmonised procedures as in "Bao M, Nobile F, Koureas M, Bottini I, Fomenko E, Brimicombe C, Tirado V, Mouchtouri V, Hadjichristodoulou C, Ljungman P, Chersich M, Jackson D, Luchters S, Stephansson O, Stafoggia M, de Bont J. Trimester-specific exposure to multiple heat indicators and adverse birth outcomes across four European countries. Environmental Research, Volume 96, 2026. https://doi.org/10.1016/j.envres.2026.124092". Data needed to repeat the analysis: Heat exposure data: Minimally: 2-m air temperature Other heat metrics: WBGT, UTCI and Heat Index Birth registry at national/subnational levem OR health facility data Minimally needed: data of birth, residential address of the mother or place of delivery Health outcome data: preterm birth (PTB), stillbirth (SB), small for gestational age (SGA), and large for gestational age (LGA). Findings from the publication referred to above: Our study included singleton births from multiple national and region registries across Europe: Sweden (2014-2019), Belgium (2012-2022), Italy (Lazio Region) (2001-2019), and Greece (1999-2021). We obtained 2-m air temperature, Universal Thermal Climate Index (UTCI), Wet Bulb Globe Temperature (WBGT), and Heat Index data from the ERA5 reanalysis dataset. Our study outcomes were preterm birth (PTB), stillbirth (SB), small for gestational age (SGA), and large for gestational age (LGA). Cox proportional hazard models, with gestational age as the underlying time scale, were applied to evaluate trimester-specific associations between multiple heat indicators and adverse birth outcomes. Country-specific estimates were then combined through meta-analyses. In total, 4,924,422 mother-child pairs were included in the analysis. An increase inmean temperature from the 75th to the 99th percentile in the third trimester was associated with PTB (HR = 1.51, 95% CI: 1.34-1.71), SB (HR = 1.54, 95% CI: 1.44-1.65), SGA (HR = 1.16, 95% CI: 1.11-1.20), and LGA (HR = 1.12, 95% CI: 1.07-1.17). Comparable associations were observed across heat indicators and countries foreach trimester. Our findings suggest that the third trimester is a critical exposure window of vulnerability for heat during pregnancy. The comparable effect estimatesamong heat indicators highlight the usefulness of mean air temperature in Europe.