Doktorarbeit

The impact of in-utero exposure to ambient temperature on maternal health, infant health, and population composition

Abstract

Climate change is leading extreme heat episodes to increase in frequency, intensity, and duration, posing a threat to population health especially in low- and middle-income countries (LMICs). In this context, extreme heat has been linked to a range of adverse birth outcomes, pointing to the sensitivity of exposure during the prenatal period. With growing populations vulnerable to extreme heat, advancing our understanding of how extreme heat impacts maternal and infant health is urgent. However, several knowledge gaps persist. Little is known about the underlying mechanisms and critical temperature thresholds that link extreme heat and maternal and infant health outcomes, the implications that these relationships have for population composition, and the extent to which heat impacts lead to socially stratified responses. In addition, various methodological approaches have led to inconsistency in findings. In this thesis, I investigate the impact of in-utero exposure to ambient temperature on maternal health, infant health, and population composition. First, I present a comprehensive methodological framework that guides the statistical analysis of temperature impacts on births with a plausible causal identification strategy. I employ this framework rigorously in three applications, the first of which investigates the impact of temperature on antenatal care visits across 52 LMICs. Results show that extreme heat impacts health-related behavior, by reducing antenatal care visits particularly for mothers in Sub-Saharan Africa who already face significant barriers in accessing healthcare. The second application studies how in-utero temperature exposure affects the sex ratio at birth, as an indicator of population composition. Exploiting socio-cultural differences in son preferences norms, I show that extreme heat reduces male birth probability in Sub-Saharan Africa and India through male-biased pregnancy loss and reductions in induced sex-selective abortions of female offspring. The third application investigates a postnatal outcome, using a case study in Mali. Here, I develop a conceptual framework on biological and behavioral pathways and show that prenatal heat exposure reduces infant mortality, most likely through intensified prenatal selection of weaker offspring. Overall, this work underlines the multiple pathways through which human reproduction and health are sensitive to the environment. The findings from this thesis serve to inform policy and intervention in vulnerable populations to safeguard the health and wellbeing of mothers and infants and prevent widening health inequities in a warming climate.