Fetal breathing movements and maternal exercise.

Earlier statements that fetal breathing movements (FBM) are sensitive to changes in the fetal homeostasis prompted the study of the effect of maternal exercise on FBM and fetal heart rate. Forty women in the last trimester of gestation were subjected to a work load (80 W) for 5 min on a bed ergometer cycle; in 30 of them FBM were recorded by A-mode ultrasound, and in 10, the fetal heart rate was monitored by continuous ultrasound. Maternal blood pressure, pulse rate, blood pH and pCO2, and transcutaneous pO2 were also followed. The FBM showed a transient marked increase in incidence immediately after the end of the exercise. No changes in basal level or in baseline variability of the fetal heart rate were found in the recovery period after work. Some possible causes of the observed FBM alterations are discussed. The findings imply that, after this particular form of stress, FBM are a more sensitive indicator of the physiological state of the fetus than the fetal heart rate.