Fetal heart rate responses to maternal exercise, increased maternal temperature and maternal circadian variation

Summary Maternal exercise resulted in an increase in fetal heart rate and variability in normal fetuses. In small fetuses there was a variable response, with four of 20 fetuses having sharp decelerations in heart rate with maternal exercise. A rise in maternal core temperature resulted, in all cases, in a rise in maternal heart rate. In normal fetuses the fetal heart rate also rose by on average 12·2 beats per min per degree Celsius. In small for dates fetuses there was no significant change in mean fetal heart rate, with three of 11 fetuses having decelerations in heart rate with increased maternal temperature. Circadian variation seen in fetal heart rates was similar to that occurring in the mother (r = 0·49, P < 0·05). There was no demonstrable circadian variation in neonatal heart rate (r= -0.24). This suggests that the fetal heart rate variation is extrinsic in origin.