Effect of water temperature on exercise-induced maternal hyperthermia on fetal development in rats

The objective of this study was to determine if water temperature influenced exercise-induced hyperthermia in swim-trained pregnant rats and the resulting fetal development. Pregnant Sprague-Dawley rats with 6 weeks pre-pregnancy training were exercised daily from day 1 to day 18 of gestation in water that was 34.6 +/- 0.4 degrees C (Cool Water Swimmers--CWS) or 37.6 +/- 0.1 degrees C (Warm Water Swimmers--WWS), for one hour/day. During this time period another group of pregnant rats was immersed to the neck in warm water (37.6 +/- 0.2 degrees C) (Warm Water Controls--WWC). On day 19 of gestation all animals were sacrificed and fetal development assessed. Maternal exercise in warm water elevated maternal body core temperature by 2.3 +/- 0.1 degrees C above resting values, with an increase in fetal abnormalities compared to the same exercise intensity in cool water. Fifty-eight percent of the abnormal fetuses and 60% of the resorption sites were found in the WWS group. Of the abnormalities determined, 65% were from the WWS group and 45% of these fetuses showed micrencephaly. Results suggest cool water may regulate maternal body temperature during swimming exercise and that swimming in warm water should be avoided during gestation because of potential teratogenic effects.