The effects of the tocolytics atosiban and nifedipine on fetal movements, heart rate and blood flow

Background. The choice of first-line tocolytic agent is a topic of worldwide debate. The oxytocin receptor antagonist atosiban and the calcium antagonist nifedipine appear to be effective in postponing delivery. However, information is lacking on their possible effects on the fetal biophysical profile. Objective. To study the direct fetal effects of tocolysis with atosiban or nifedipine combined with a course of betamethasone. Method. We performed a randomised controlled study including women with preterm labour requiring tocolytic treatment. Primary outcome measures were the effects on fetal heart rate (FHR) and its variation. Secondary endpoints were the effects on fetal movement and blood flow (pulsatility index-PI) of the umbilical (UA) and medial cerebral arteries (MCA). Results. One-hour recordings of FHR and fetal movements were made on each of five successive days (days 0-4). Fetal blood flow velocity patterns were studied daily by Doppler ultrasound. Baseline characteristics of 31 women who had not delivered at day 0 and needed no escape tocolysis did not differ between the study groups. Multilevel analysis showed no significant effect of either tocolytic on FHR and movement parameters over the 5-day study period. The use of tocolytics also did not significantly alter the time courses of PI-values for UA (p-0.37) and MCA (p-0.62). Conclusion. This study demonstrates for the first time the direct effects of atosiban on fetal movement, heart rate and blood flow. Tocolysis with either atosiban or nifedipine combined with betamethasone administration appears to have no direct fetal adverse effects.