Assessment of Maternal Nifedipine as a Tocolytic Agent on the Doppler Indices of Uterine and Fetal Umbilical and Middle Cerebral Arteries

Abstract

Objective: This study was designed to assess the effects of maternal nifedipine administration on blood flow resistance in uterine, umbilical and fetal middle cerebral arteries by evaluating resistance index (RI) and pulsatility index (PI).
Patients and Methods: This was a prospective, observational, analytic cohort study performed in 50 pregnant women undergoing nifedipine tocolysis, all women with a singleton pregnancy between 24 and 34 weeks of gestation, each subject acting as her own control. Doppler assessment of uterine, umbilical and fetal middle cerebral (MCA) arteries was performed before and 24 h and 72 h after an initial 20 mg oral dose, which was repeated at 20 min intervals if contractions failed to diminish up to a total maximum dose of 60 mg. The maintenance dose consisted of 20 mg orally every 6 h. We analyzed whether there was a time effect and compared values at the different time-points.
Results: The research showed that the UtA-RI has increased significantly after 24 h and after 72 h of nifedipine administration (0 h=0.53; 24 h=0.56; 72 h=0.55; p=0.002, p=0.015 respectively). The MCA-RI had decreased significantly after 24 h (p=0.003) of tocolysis returning to baseline after 72 h (0 h=0.75; 24 h=0.73; 72 h=0.74; p=0.150). The MCA-PI had decreased significantly after 24 h (P=0.024) of tocolysis returning to baseline between 24 h and 72 h (0 h=1.85; 24 h=1.75; 72 h=1.79; p=0.204), with no differences in UtA-PI or in the umbilical arteries Doppler (RI & PI) or in the MCA to umbilical artery ratio.
Conclusions: Nifedipine tocolysis is associated with a reduction in RI and PI in the MCA, and an increase in RI in uterine arteries after 24 h but returning to baseline within 72 h, with no long-term effect on fetomaternal circulation in pregnant women at risk of preterm delivery.