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

## TL;DR

Pregnant endurance athletes have higher water needs due to physical activity and heat stress, which could impact policy for vulnerable populations.

## Contribution

This study quantifies how physical activity and heat stress interact to influence water turnover in pregnant athletes.

## Key findings

- Athletes had consistently high water turnover from preconception through pregnancy.
- Physical activity was positively linked to water turnover in early pregnancy but not in the third trimester.
- Higher heat index conditions slightly strengthened the relationship between physical activity and water turnover.

## Abstract

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.

We recruited 20 female endurance runners who were pregnant (8–16 weeks gestational age; n = 13) or planning to be pregnant (n = 7) for an observational, prospective cohort study. At three timepoints in the study (preconception, 8–16 weeks, and 32–35 weeks), we measured water turnover (WT) using the deuterium dilution and elimination technique, PA using ActiGraph wGT3X-BT accelerometers, and heat index (HI) using historical temperature and humidity data. We also compared athletes to nonathletes from a previously published study.

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.

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.