Thermal response to submaximal exercise before, during and after pregnancy: a longitudinal study

Background: Heat stress in early pregnancy is known to have a teratogenic effect. Exercise produces excess heat and during pregnancy might therefore present a theoretical risk of malformations. Our aim was to assess the thermal response to exercise of healthy pregnant women in a longitudinal study. Methods: Fourteen women were examined before pregnancy, and followed five times during, and twice after pregnancy, using a submaximal bicycle test with a target heart rate of 85% of the predicted age-adjusted maximum. The main aim was to present reference values. Results: The temperature at submaximal work load declined continuously from preconception to postpartum levels (37.8°C vs. 36.9°C, p = 0.04). The difference between peak and basal core temperature fell from 0.6°C to 0.05°C at 29 and 36 weeks of gestation, reaching preconception levels at 24 weeks after delivery (0.8°C lower). Conclusion: During submaximal exercise the temperature response seemed to provide thermal protection for the embryo and the fetus.