Effect of maternal betamethasone on fetal and uteroplacental blood flow velocity waveforms.

Abstract
OBJECTIVES:
To investigate the effects of antenatal betamethasone on fetal and uteroplacental hemodynamics.

METHODS:
The study comprised 33 women with singleton high-risk pregnancies (23-33 weeks; 27 pregnancies < 30 weeks) not in labor, but at risk for preterm delivery based on fetal or maternal indications. They were treated with two doses of 12 mg betamethasone intramuscularly 24 h apart to enhance fetal lung maturity. Flow velocity waveforms were recorded with Doppler ultrasound from the umbilical artery, the fetal middle cerebral artery, the ductus venosus and both maternal uterine arteries, once before and twice after betamethasone administration.

RESULTS:
Twenty-one (64%) women delivered within 4 days, nine (27%) women within 5-7 days and three (9%) within 8-15 days after the first dose of betamethasone. Two days after betamethasone, a decrease in pulsatility index was found in the umbilical artery (P = 0.0002) and ductus venosus (P = 0.003). Changes in the umbilical artery waveform from reversed to absent, and from absent to positive diastolic flow, were noted in 12 of 15 cases (P < 0.01). After 4 days, umbilical artery and ductus venosus velocity waveforms in the undelivered fetuses either returned to the type of waveform observed before treatment or showed further deterioration. No significant effects of betamethasone were observed in the fetal middle cerebral artery and uteroplacental circulation.

CONCLUSIONS:
Maternal antenatal betamethasone resulted in a significant transient change in the velocity waveform and a decrease in the pulsatility index in the umbilical artery and ductus venosus, but did not influence uteroplacental circulation. These findings indicate a direct effect of betamethasone on fetal circulation