Heat exposure and adverse pregnancy outcomes: evidence from humans and other viviparous species

Recent studies reveal a connection between heat exposure during pregnancy and unfavorable birth outcomes in various species, including humans. Global warming is leading to more intense heatwaves, posing risks to maternal and fetal health worldwide. Multiple investigations have found associations between elevated temperatures during pregnancy and conditions such as preterm birth, low birthweight, and stillbirth.

The shared mechanisms behind these adverse outcomes are believed to involve maternal inflammation, dehydration, and alterations in placental function. The impact of heat exposure on pregnancy seems to vary depending on the stage of gestation and the specific species involved. In particular, exposure to high temperatures during the third trimester appears to elevate the risk of preterm birth and reduced birthweight.

A comprehensive review of 197 studies encompassing ten species, including humans, cows, sheep, pigs, goats, rats, mice, guinea pigs, lizards, and rabbits, has identified these consistent patterns and trends. Many researchers emphasize the role of the placenta in contributing to adverse outcomes, suggesting that heat exposure may disrupt placental physiology or cortisol signaling pathways.

Understanding the relationship between heat exposure and adverse birth outcomes, as well as the underlying mechanisms and timing, is crucial for developing public health policies and implementing strategies to protect pregnant individuals during periods of extreme heat.