Effect of Intravenous Tocolytics on Uteroplacental and Fetoplacental Doppler Flow Velocity Waveforms

Abstract

The vasodilatory effects of ritodrine hydrochloride and magnesium sulfate (MgSO₄) were investigated by analyzing fetoplacental and uteroplacental Doppler flow velocity waveforms (FVWs) obtained from pregnant women about to undergo external version for abnormal fetal lie. These healthy women were chosen for study because they were known to have uncomplicated pregnancies at 37-38 weeks gestation by a reliable last menstrual period and confirming ultrasound. Twenty patients were studied with continuous wave Doppler ultrasound immediately prior to and at least 30 min after intravenous infusion of 100 μ.g/min of ritodrine, and 20 patients were studied before and after the administration of a 6 g intravenous bolus of MgSO₄. No statistically significant alterations of maternal or fetal FVW systolic to diastolic (S/D) ratios were detected after administration of either ritodrine or MgSO₄. We conclude that the intravenous infusion of 100 μ.g/min of ritodrine hydrochloride or 6 g of MgSO₄ in normal healthy women at term has no effect on impedance to placental perfusion as measured by Doppler ultrasound.

Key Words:

• Doppler
• Ritodrine
• Magnesium sulfate