Human fetal ductal flow velocity waveforms relative to behavioral states in normal term pregnancy.

In 16 normal pregnancies the relationship between the blood flow velocity waveform and fetal behavioral states at 37 to 38 weeks' gestation was studied. Whereas behavioral state independency was established for the acceleration time, peak flow velocity demonstrated a statistically significant reduction during active sleep, compared with quiet sleep. These data reflect reduced ductal flow and suggest a redistribution in the left-ventricular and right-ventricular output in favor of the left side of the heart during active sleep. Peak flow velocities in the fetal ductus arteriosus were independent of fetal heart rate.