The Effects of Heat Stress on the Ovary, Follicles and Oocytes: A Systematic Review†.

Climate change is driving significant environmental changes with profound implications for human health, including fertility. Although the detrimental effects of heat on spermatogenesis are well-documented, the impact of elevated temperatures on ovaries and female fertility remains less explored. This systematic review evaluates the effects of elevated temperature exposures (heat stress, HS) on the ovary, follicles, and oocytes across a range of mammalian species. Drawing from both in vivo and in vitro studies, we synthesize findings that show HS can impair ovarian function by disrupting reproductive hormone profiles, reducing ovarian size and weight, altering ovarian histology, and inducing autophagy. At the cellular level, HS leads to increased granulosa cell apoptosis, impaired folliculogenesis, and decreased oocyte quality and developmental competence. However, inconsistencies across studies highlight the influence of experimental variation, including differences in species, timing, intensity, and duration of HS exposure. While many studies report detrimental effects, a few suggest possible adaptive responses under certain conditions. Finally, we review emerging interventions, including antioxidants, hormone supplementation, and bioactive compounds, that aim to counteract HS-related reproductive damage. Despite progress, further research is urgently needed to define conserved molecular pathways, optimize experimental models, and inform clinical strategies to protect fertility and reproductive lifespan in a warming world.