Prenatal exposure to extreme temperatures and neonatal health in Lausanne 1909 to 1912

BackgroundExtreme temperatures are increasingly recognized as risk factors for maternal and neonatal health, but historical evidence remains scarce. This study investigates the association between prenatal exposure to extreme heat and cold and neonatal health outcomes in Lausanne, Switzerland, during 1909-1913, including the exceptional 1911 heatwave. Data & MethodsWe digitized and linked daily minimum and maximum temperature data from the Champs-de-lAir weather station with 2,000 maternity records from Lausannes hospital (1909-1913). Continuous outcomes included birth weight, gestational age, placenta weight, birth length, and head circumference; binary outcomes were low birth weight (LBW, <2,500g) and preterm birth (PTB, <37 weeks). Daily mean temperature exposure was averaged over whole pregnancies and trimesters. Associations were estimated using generalized linear models for continuous outcomes and Cox proportional hazards for binary outcomes, adjusting for maternal and seasonal covariates. ResultsInfants exposed to extreme heat (>90th percentile) or cold (<10th percentile) throughout pregnancy had consistently poorer outcomes compared with moderate exposure. Whole-pregnancy exposure to the 95th percentile temperature was associated with -211g lower mean birth weight and -1.1 weeks shorter gestation relative to median exposure. Cold exposure was linked to increased LBW risk but less strongly to shortened gestation. In unadjusted analyses, LBW prevalence was 25% under high-temperature exposure versus 10% at moderate levels; PTB prevalence was 26% versus 9%. Stillbirth and early neonatal mortality rates were also higher at temperature extremes. Effects were strongest for third-trimester exposure and more pronounced for heat than for cold. ConclusionThis study provides rare historical evidence that both heat and cold during pregnancy adversely affected neonatal health in early 20th-century Switzerland, with heat exposure during the 1911 heatwave particularly detrimental. These findings underline that vulnerability of pregnant women and newborns to temperature extremes might be a long-standing phenomenon.