Fetal heart patterns. A study of the anencephalic fetus.

The anencephalic fetus is an interesting model for the study of the fetal heart rate (FHR). Such a fetus could serve as a model for the examination of the effect of "intracranial" pressure on the FHR, because its central nervous system (CNS) is directly exposed to intraamniotic pressure changes. The FHR was monitored in 10 anencephalic fetuses of normal, uncomplicated pregnancies and of gestational age between 35 and 42 weeks. Silent-pattern heart rate was observed in 6 of the monitored anencephalic fetuses. No other consistent heart rate pattern was obtained. A relatively high incidence of extreme early decelerations may be attributed to the exposure of the fetal CNS to direct pressure.