Climate change poses important challenges to public health and for pregnant individuals. Exposure to heat during pregnancy could be particularly detrimental for the fetus and lead to negative birth outcomes such as low birth weight (LBW) very low birth weight (VLBW) and pre-term birth (PTB). The reason for this is that extreme heat might increase the mother’s body temperature outside the comfort zone for a prolonged time resulting in hyperthermia. Imbalances in the mother’s body temperature are consequential for the fetus as it heavily relies on the mother for its own thermoregulation.
Importantly, sociodemographic characteristics, such as the socioeconomic status (SES) of pregnant individuals, could determine disparities in exposure and vulnerability to heat. Higher SES individuals are more likely to be less exposed to heat as residing in greener areas of cities or because they own air conditioning. Moreover, when exposed to heat, they might be overall healthier or have access to critical social or medical support.
In their study, Risto Conte Keivabu and Marco Cozzani (European University Institute) focus on Spain to uncover the impact of heat on birth outcomes and the stratified effect of SES. They do so by leveraging data on temperature and birth outcomes from 1990 to 2016 in 50 provincial capitals covering more than 4 million live births. Their results show hot days (temperature above 32°C) negatively affect birth outcomes increasing the occurrence of VLBW and LBW, especially when exposure occurred early in the pregnancy. Importantly, they observe the effect to be stratified by SES. Low SES individuals are more likely to suffer from exposure to heat and deliver infants with LBW or VLBW. For example, the increase in the incidence of LBW with exposure to days above 32°C in the second trimester is of 0.085 percentage points for low SES individuals. Conversely, some High SES individuals show a negative coefficient with exposure to heat suggesting a decrease in risk, likely attributable to compensatory mechanisms.
Climate change makes these results particularly concerning. Health at birth is an important predictor of future life outcomes, such as educational attainment and income. Consequently, the SES gradient observed in the impact of heat could have implications on how climate change will shape socioeconomic inequalities in the future.