1. Background

As global temperatures continue to rise, it is becoming increasingly important to understand how heat exposure may affect vulnerable populations such as pregnant mothers and their offspring.  While multiple studies have linked heat exposure during pregnancy and adverse birth outcomes such as preterm birth, low birth weight and embryo loss, underlying mechanisms and critical windows of exposure are not yet fully understood. 

1. Methods

To address this, we conducted a scoping review on heat exposure and pregnancy outcomes across viviparous species, to identify common mechanisms and any critical windows of exposure. We examined temperature-, temporal- and species- specific patterns across 197 studies and ten species (human, cow, sheep, pig, goat, rat, mouse, guinea pig, lizard and rabbit).

1. Results

 Across species, heat exposure was associated with adverse birth outcomes. A third of included human studies identified the third-trimester exposure as a potential critical window for preterm birth, and about a fifth identified it as a potential critical window for low birth weight. Studies additionally emphasise placental involvement in adverse outcomes and point to potential aberrations in placental physiology or cortisol signalling pathways, however mechanistic evidence remains limited in humans due to experimental constraints.

1. Conclusion

Overall, this review highlights that heat exposure increases risk of adverse birth outcomes across studies, and taxa, while additionally identifying gaps in our understanding if the biological mechanisms. Improving our understanding of these mechanisms and critical windows of exposure will be vital for mitigating the effects of climate change on pregnancy.