Single Dose of Labetalol in Normotensive Pregnancy: Effects on Maternal Hemodynamics and Uterine and Fetal Flow Velocity Waveforms

Abstract

The short-term effect of 0.8 mg/kg of intravenous bolus of labetalol upon maternal and fetal hemodynamics was investigated in 10 healthy women at 38 weeks of gestation admitted to the hospital for elective cesarean section. The maximum effect occurred within 35 min after labetalol. At that point, the mean arterial pressure had decreased by 16%, and a slight decrease was observed in maternal heart rate. As to the flow velocity waveforms, no significant change was found in mean systolic/diastolic (S/D) ratio of uterine artery, umbilical artery or fetal middle cerebral artery. However, in 2 subjects with a large decrease in blood pressure also the uterine artery S/D ratio decreased.

Single dose of labetalol in hypertensive pregnancy: Effects on maternal hemodynamics and uterine and fetal flow velocity waveforms

“…The antihypertensive effect of labetalol in the hypertensive subjects was clear: the nadir of BP occurred 30 -35 minutes after labetalol infusion. In a study with normotensive subjects the drop in BP followed the same time course [7]. The mean drop in MAP was 18% which agrees with previous studies with the same dose of labetalol [5,11] and also with our previous study with normotensive subjects [7].…”

“…In a study with normotensive subjects the drop in BP followed the same time course [7]. The mean drop in MAP was 18% which agrees with previous studies with the same dose of labetalol [5,11] and also with our previous study with normotensive subjects [7]. The antihypertensive effect remained measurable for more than one hour.…”

Maternal and fetal haemodynamic effects of nifedipine in normotensive pregnant women

“…Nifedipine readily crosses the placenta with a maternal/ fetal plasma ratio of 0.93. 3 Despite significant changes in maternal haemodynamics we could not demonstrate any changes in the uterine, umbilical or middle cerebral pulsatility indices or time-averaged maximum velocities. This suggests that nifedipine has no effect on the uteroplacental or fetal circulation but the limitations of both measurements in reflecting total blood flow should be noted.…”

“…2,9 Another study observed a significant decrease in uterine artery resistance but without changes in the arcuate or umbilical artery Doppler flows. 3 The absence of changes in the uterine circulation is remarkable considering the substantial maternal afterload reduction. It indicates that in healthy normotensive pregnancy without signs of placental insufficiency, trophoblast invasion has lowered downstream resistance to such an extent that nifedipine is unable to further reduce uterine resistance, despite its potency to reduce the systemic resistance.…”

“…1 Nifedipine does not seem to affect blood pressure significantly in normotensive pregnant women, despite high-dose regimens. [1][2][3][4] Nevertheless, there are some concerns on its safety. 5,6 Rare but serious maternal cardiopulmonary and fetal complications have been reported in both humans and animals after tocolysis with calcium channel blockers.…”