Fetal heart rate variability as an indicator of fetal status.

Numerous studies have shown the clinical usefulness of monitoring fetal heart rate (FHR) variability. Among the disorders associated with decreased FHR variability during labor are fetal asphyxia and acidosis and subsequent distress in the newborn. Among the factors that influence FHR variability are maternal fever, fetal immaturity, so-called fetal sleep, fetal tachycardia, and drug administration to the mother. The nonstress test, which analyzes FHR variability and accelerations of heart rate with fetal movements, may be as useful as the oxytocin challenge test for assessing FHR variability. Doppler ultrasonic cardiography exaggerates the amount of FHR variability. FHR patterns associated with progressive loss of beat-to-beat variability in the absence of maternal drug intake necessitate intervention.