Single dose of nifedipine in normotensive pregnancy: nifedipine concentrations, hemodynamic responses, and uterine and fetal flow velocity waveforms.

The short-term effect of 20 mg of oral nifedipine on maternal and fetal hemodynamics was investigated in ten healthy, normotensive women at 38 weeks' gestation admitted to the hospital for elective cesarean delivery. Within 1 hour after nifedipine administration, mean arterial pressure had decreased by 10% and a slight increase was observed in maternal heart rate. A statistically significant (P less than .01) decrease in the systolic-diastolic ratio was found in the flow velocity waveform from the uterine artery, but no change was seen in that from the arcuate artery. No changes were observed in the fetal heart rate pattern or in umbilical or thoracic aortic flow velocity waveforms. Nifedipine concentrations in the mother had no correlation with maternal or fetal hemodynamic responses. At delivery 2.5 hours after nifedipine ingestion, the umbilical venous-maternal ratio of nifedipine concentrations was 0.76.