Severe fetal supraventricular bradyarrhythmia without fetal hypoxia.

Cardiac anatomy and rhythm were evaluated in a fetus at 39 weeks' gestation in a pregnant woman referred because of severe fetal bradycardia with a persistent fetal heart rate of 50-60 beats per minute. M-mode echocardiograms revealed supraventricular bradyarrhythmia. Umbilical cord blood analysis did not, however, reveal fetal hypoxia. Diagnostic methods of fetal bradyarrhythmia are discussed, and the importance of differentiating bradyarrhythmia from bradycardia due to fetal hypoxia is emphasized.