Maternal and Fetal Blood Flow Velocity Waveforms in Patients With Preterm Labor: Effect of Tocolytics

The effect of tocolytics on systolic to diastolic (S/D) ratios used to assess downstream vascular resistance and obtained from umbilical and uterine velocity waveforms has not been studied to date. Continuous-wave Doppler studies were performed on the umbilical and uterine arteries of 60 consecutive patients with the diagnosis of preterm labor. Forty patients receiving intravenous magnesium sulfate and 20 patients receiving intravenous ritodrine tocolysis underwent Doppler studies before therapy, during incremental therapy, and four hours post-therapy. There was a statistically significant (P