Alterations in maternal-fetal Doppler flow velocity waveforms in preterm labor patients undergoing magnesium sulfate tocolysis.

OBJECTIVE

To evaluate the effects of magnesium on fetal hemodynamics in mothers treated with magnesium sulfate for preterm labor.

METHODS

Twenty women who presented to the Carolinas Medical Center in preterm labor between 24-35 weeks' gestation were enrolled in the study. Pulsed-wave Doppler measurements were made from the fetal middle cerebral artery, the fetal umbilical artery, and the maternal uterine arteries before the initiation of magnesium sulfate tocolysis and during its intravenous administration. Baseline measurements were compared with intra-therapy measurements using paired t tests.

RESULTS

During the administration of magnesium sulfate, the fetal middle cerebral artery diastolic blood flow velocity decreased significantly (P = .05) and the maternal uterine artery diastolic blood flow velocity increased significantly (P = .01). There were no significant changes in the umbilical artery diastolic blood flow measurements. These findings remained the same after adjusting for gestational age, estimated fetal weight, frequency of contractions, serum magnesium level at the time of the intra-therapy Doppler study, and maternal blood pressure.

CONCLUSION

The alterations in fetal hemodynamics during magnesium sulfate administration suggest a physiologic normalization process related to the stressed preterm infant and the preterm labor process itself.