Physical activity and heat stress shape water needs in pregnant endurance athletes.

Background and objectives: Pregnancy, heat stress, and physical activity (PA) are all known to independently increase human water requirements. We hypothesize that climate conditions and behavioral strategies interact to shape water needs in highly active pregnancies. Methodology: We recruited 20 female endurance runners who were pregnant (8-16 weeks gestational age; Results: Athletes maintained high WT from preconception through the end of pregnancy. PA was positively associated with WT among athletes for preconception and early pregnancy time periods but not for the third trimester. HI weakly moderated the relationship between PA and WT in predicting a more positive slope in hotter and more humid weather conditions. WT in athletes was higher than in nonathletes, but this difference attenuated during the third trimester, as nonathletes increased their WT. Conclusions and implications: Athletes experience higher WT with greater levels of PA, and this relationship is somewhat stronger in higher HI conditions. With the threat of climate change expected to exacerbate extreme heat conditions, evidence-based, global policies are required for particularly vulnerable populations.