Key result
Hydralazine and labetalol both lower maternal blood pressure, but exert opposing effects on umbilical artery pulsatility.
RCT (n=30)
Randomly allocated
Intravenous treatment with 10 mg of hydralazine or 100 mg of labetalol was randomly allocated to 30 hypertensive pregnant women. Umbilical artery flow velocity waveforms were recorded using a pulsed Doppler duplex scanner (ATL Mk V) and umbilical artery pulsatility index (PI) and fetal heart rate (FHR) were derived from these recordings. Maternal blood pressure decreased significantly after both drugs. Maternal pulse rate increased after hydralazine but did not change significantly after labetalol. FHR did not change significantly after hydralazine but decreased after labetalol. PI decreased after hydralazine and increased after labetalol--most fetuses showed little change but a few in each group showed large changes in PI, as did two of five additional patients studied. We attributed the decrease in PI in some fetuses after hydralazine to vasodilation, and the increase in PI in some fetuses after labetalol to vasoconstriction in the fetoplacental circulation, suggesting that fetal beta-blockade may occur after maternal treatment with labetalol.
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Harper et al. (1991) conducted an RCT in Hypertensive pregnancy (n=30). Intravenous hydralazine vs. Intravenous labetalol (100 mg) was evaluated on Maternal blood pressure, maternal pulse rate, fetal heart rate (FHR), and umbilical artery pulsatility index (PI). Intravenous hydralazine and labetalol both significantly decreased maternal blood pressure, but hydralazine decreased umbilical artery pulsatility index while labetalol increased it.
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