48-hours administration of nifedipine in spontaneous preterm labor - Doppler blood flow assessment of placental and fetal circulation

OBJECTIVES: The aims were to assess the placental and fetal circulation during nifedipine tocolysis within the first 48 hours of therapy. METHODS: Placental and fetal circulation was assessed in Doppler ultrasound examination prior to nifedipine administration and then after 24 and 48 hours. Maternal heart rate and PI in uterine arteries were evaluated as well as FHR, RI and PI of UA and MCA. E/A-wave ratio for A-V valves, MPI and SF were calculated for both ventricles independently. To determine changes over time in all study variable analysis of variance (ANOVA) for repeated measurements followed by Tukey-Kramer's multiple comparison test was used. The effects of additional clinical covariates were checked. RESULTS: Uterine and umbilical blood flow patterns were not altered significantly during administration of nifedypine tocolysis. While MCA Doppler indicies such as RI and PI were unchanged, the evaluation of MCA PSV revealed a transient significant decrease after 24 hours. A resolution of this distraction was observed within the following 24 hours. No significant changes were observed in direct fetal cardiac function parameters calculated separately for both ventricles. CONCLUSIONS: The decrease of MCA PSV after 24 hours of treatment was isolated and transient hemodynamic distraction observed during treatment. Neither fetal cardiac parameters nor other Doppler indices were changed. Therefore oral administration of nifedipine seems not to alter uterine nor fetal arterial blood flow pattern seriously. As significant changes were observed by different authors, further studies should be performed to verify the optimal total dose of nifedipine and its influence on hemodynamic conditions.