Fetal heart rate response to sustained recreational exercise

We aimed to test the hypotheses that fetal heart rate increases during and after sustained exercise and that the magnitude of the increases is related to gestational age and the duration, intensity, and type of exercise.

Maternal oxygen uptake and fetal heart rate were monitored in 120 regularly exercising women in association with routine 20-minute workouts between 16 and 39 weeks' gestation.

In 97% of the studies fetal heart rate increased during and after exercise. This was significant at all gestational ages and with all forms of exercise with an overall increase of 15 +/- 11 beats.min-1 at 60% +/- 12% of maximal aerobic capacity (mean +/- SD). The magnitude increased with gestational age (10 +/- 8 to 20 +/- 11 beats.min-1), exercise intensity (8 +/- 7 to 21 +/- 13 beats.min-1), and exercise duration (8 +/- 4 to 16 +/- 7 beats.min-1).

We concluded that the hypothesis is correct and speculate that these changes represent a maturing fetal response to a reduction in Po2.