The effects of maternal exercise on fetal heart rate and movement patterns.

The aim of this study was to investigate the effects of maternal exercise on fetal movement and heart rate patterns. Twelve healthy women at 29-32 weeks of pregnancy performed a (sub)maximal bicycle exercise test, reaching 53-99% (median 82%) of their maximal increase in heart rate (MIHR). Fetal heart rate (FHR) and its variation and fetal body and breathing movements were recorded for 1 h before and after the exercise and also on a control day. After exercise, FHR was higher for 30 min and FHR variation reduced for 20 min as compared with pre-exercise levels (P < 0.01). Fetal body movements were reduced for the first 5 min following exercise (P < 0.05). In two cases, fetal bradycardia was observed (at 89 and 99% MIHR) followed by a considerable reduction in FHR variation and absence of body and breathing movements for 20 min. In the other 10 fetuses fetal breathing activity was increased for the first 5 min after exercise (P < 0.05). FHR (and to a lesser extent breathing movements) increased with increasing level of maternal exercise, but decreased when the % MIHR exceeded approximately 90%. Body movements were negatively correlated with the % MIHR (P < 0.05). In conclusion, moderate to heavy maternal exercise clearly affects the human fetus with signs of transient fetal impairment after heavy exercise.