Uterine and fetal flow velocity waveforms in hypertensive pregnancy: the effect of a single dose of nifedipine.

The short-term effect of 20 mg of oral nifedipine on maternal and fetal hemodynamics was investigated in 12 women with pregnancy-induced hypertension. Within an hour after nifedipine, the mean arterial blood pressure fell by 17% and there was a slight increase in maternal heart rate. There was also a decrease in the systolic/diastolic (S/D) ratio in the flow velocity waveform in the uterine artery in seven subjects, whereas the S/D ratio was unaffected in five subjects. Lack of change in the S/D ratio was associated with a less optimal pregnancy outcome: The neonates were delivered earlier, the rate of cesarean delivery was higher, and the newborns were smaller. No changes were observed in the fetal heart rate pattern or in the umbilical or middle cerebral artery flow velocity waveforms after nifedipine in hypertensive pregnancies.