A comparison of the effects of the most commonly used tocolytic agents on maternal and fetal blood flow

OBJECTIVE: To investigate the effects of two tocolytics, nifedipine and magnesium sulfate, on Doppler indices in maternal and fetal vessels. MATERIALS AND METHODS: We recruited 100 pregnant women with preterm birth between 24-36 gestational weeks who were admitted to our tertiary center over a two-year period. Patients were allocated to nifedipine (n=49) and magnesium sulfate (n=51) groups and Doppler indices of umbilical, middle cerebral, uterine arteries, and ductus venosus were measured before and after tocolysis. RESULTS: There were no differences between the groups in terms of maternal age, gestational week, body mass indexes, cervical dilation, effacement at admission, birth weights and latency periods until birth. Nifedipine decreased resistance indexes in uterine arteries but magnesium sulfate increased resistance especially in the right uterine artery. Nifedipine significantly decreased systole to diastole and resistance index in the umbilical artery, magnesium sulfate increased systole to diastole and resistance index but this was not statistically significant. Nifedipine acted variably on resistance index and pulsatility index in the ductus venosus; however, magnesium sulfate increased resistance. Nifedipine decreased pulsatility index in the middle cerebral artery, contrary to magnesium sulfate with which it increased. CONCLUSION: Nifedipine had favorable effects on maternal and fetal vessel indexes but magnesium sulfate increased resistance. Despite the proposed neuroprotective benefits of magnesium sulfate, nifedipine seems to be a better and safer tocolytic agent than magnesium sulfate due to its positive beneficial effects on maternal and fetal vessels.