The effect of maternal exercise on fetal heart rate

One hundred and ninety-three women with uncomplicated pregnancies and 44 with high-risk pregnancies participated in a 5-minute exercise stress test on a bicycle ergometer. All women were in the third trimester of pregnancy. Measurements of fetal heart rate were made at intervals of 2, 4, 6, 8, 10, 12, 16, 20, 25 and 30 minutes. Fetal heart rate was then compared in terms of maternal age, parity, consumption of cigarettes, exercise intensity, history of activity, cardiotocography score, maternal heart rate at rest, maternal heart rate after exercise, fetal sex and birth weight. In low-risk pregnancies an increase in fetal heart rate from 143 (124-171) beats per minute (bpm) to 148 (116-191) bpm was noted after exercise while, in the high-risk pregnancy group, a transient decrease from 148 (115-170) bpm to 141 (70-180) bpm was observed. There were also 10 cases of significant bradycardia in the high-risk pregnancy group. We conclude that the effect of maternal exercise on fetal heart rate is dependent on many variables. A fetal bradycardia following exercise is more likely to occur in high-risk pregnancies. The use of fetal heart rate variation with exercise could be a useful prognostic factor in pregnancy.