Effect of acute hypoxia on human fetal heart rate. The significance of increased heart rate variability.

The fetal heart rate response to acute hypoxemia was observed during an accidental drop in oxygen concentration inspired by the mother in labor. There was a marked increase in FHR variability in the early stage of hypoxia and also during the recovery phase. While an increase in fetal heart variability is generally considered to be a normal physiological event, it may also indicate a state of fetal hypoxemia associated with an intact fetal circulation, and should be treated with caution during labor.