Fig. 1.

Overview of births and preterm births, course of ambient temperature, the city of Hamburg with the meteorological station,and schematic overview of the experimental design of the analysis, utilizing data from the registry and PRINCE study. (a) Total number of births (grey bars, left Y axis) and percentage of preterm births (solid black line, right Y axis) per year, documented at the University Medical Centre Hamburg-Eppendorf between 1999 and 2021. (b) Average maximum temperature between March and September in Hamburg, Germany during the period 1999–2021 (black line) and heat map depicting the increase in maximum ambient temperatures. Insert: course of average maximum temperature increase (March–September) per year between 1936 and 1998. The colour codes of the heat maps depict the deviation from the mean for each year. (c) The city of Hamburg with the exact location of the University Medical Centre Hamburg-Eppendorf and the federal meteorological monitoring station. Grey circles represent varying distances from the monitoring station. Percentages indicate the residential addresses of registry study participants. (d) Overview of the study design and schematic depiction of the methodological work flow of the two main analyses.