Fetal heart rates during maternal wakefulness and sleep.

This study was designed to provide normative data on fetal heart rate (FHR), FHR variability, accelerations, and decelerations during maternal sleep in the third trimester of pregnancy and to identify rhythmicity in FHR variability. Twenty-four polygraphic recordings were obtained in 16 pregnant women at 32 and 36 weeks' gestation. FHR parameters were not predictably influenced by maternal sleep states. Cyclic changes in FHR variability with median cycle length of 53 minutes were observed. Accelerations and decelerations occurred an average of 12.2 and 4 times per 100 minutes, respectively. Bradycardia and tachycardia persisting beyond 10 minutes were not seen. FHR variability ranged from marked to decreased within recordings of the same subject; this observation has implications for non-stress testing of the fetus.