Effects of magnesium sulfate on preterm fetal cerebral blood flow using doppler analysis: A randomized controlled trial

Objective: To estimate the effects of maternal administration of magnesium sulfate on the fetal middle cerebral artery using Doppler. Methods: This is a single-center ancillary study done in conjunction with a randomized, double-masked, placebo-controlled trial in 20 centers. Women at imminent risk of preterm delivery (n=2,241) were allocated randomly to receive magnesium sulfate or placebo. Doppler measurements of the fetal middle cerebral artery were obtained before blinded study-drug administration and subsequently at 1-, 2-, 3-, and 4-hour intervals. Parameters studied included time-average velocity, peak systolic velocity, vessel diameter, heart rate, and calculated blood volume flow. A random-effects model with repeated-measures design was used for analysis. Results: A total of 38 fetuses were studied: 18 received magnesium sulfate and 20 received placebo. Peak systolic velocity was significantly related to gestational age (P<.001). There were no differences between the study groups for middle cerebral artery peak systolic velocity, average velocity, vessel diameter, or calculated volume flow. However, fetal heart rate significantly decreased after treatment with magnesium sulfate. CONCLUSION: Magnesium sulfate had no significant effects on fetal cerebral blood flow analyzed using Doppler. The only parameter in the fetal cerebral circulation significantly modified by magnesium sulfate was the heart rate. The significance of this heart-rate change, vis-à-vis the neuroprotective effects of magnesium sulfate, is unknown.