OBJECTIVES: In fetuses with a single umbilical artery the entire blood flow to the placenta is transported through the common and internal iliac arteries from the side of the single artery, whereas the pelvic vessels from the side of the missing artery do not participate in the fetoplacental circulation. The aim of this study was to investigate the effect of gestational age on pelvic arterial blood flow in fetuses with single umbilical artery. DESIGN: In 15 fetuses with a single umbilical artery (SUA), common iliac artery flow velocity waveforms were studied longitudinally using high resolution colour Doppler ultrasonography at three gestational ages: 18 to 20 weeks, 28 to 30 weeks, and 35 to 37 weeks. The pulsatility index was measured in each common iliac artery and mixed model analysis of variance was used to examine the effect of gestational age and side. RESULTS: There was a highly significant difference in pulsatility index between common iliac arteries at all gestational ages, the values always being higher on the side that did not participate in the fetoplacental circulation (P < 0.001). For increasing gestation, the pulsatility index fell significantly in the SUA side but remained high in the non-SUA side (P < 0.001). CONCLUSIONS: This study shows that the asymmetry in the pelvic arterial blood flow in fetuses with SUA increases as pregnancy progresses, consistent with decreasing vascular resistance in the placenta and increasing resistance in the lower extremities.
OBJECTIVES: In fetuses with a single umbilical artery the entire blood flow to the placenta is transported through the common and internal iliac arteries from the side of the single artery, whereas the pelvic vessels from the side of the missing artery do not participate in the fetoplacental circulation. The aim of this study was to investigate the effect of gestational age on pelvic arterial blood flow in fetuses with single umbilical artery. DESIGN: In 15 fetuses with a single umbilical artery (SUA), common iliac artery flow velocity waveforms were studied longitudinally using high resolution colour Doppler ultrasonography at three gestational ages: 18 to 20 weeks, 28 to 30 weeks, and 35 to 37 weeks. The pulsatility index was measured in each common iliac artery and mixed model analysis of variance was used to examine the effect of gestational age and side. RESULTS: There was a highly significant difference in pulsatility index between common iliac arteries at all gestational ages, the values always being higher on the side that did not participate in the fetoplacental circulation (P < 0.001). For increasing gestation, the pulsatility index fell significantly in the SUA side but remained high in the non-SUA side (P < 0.001). CONCLUSIONS: This study shows that the asymmetry in the pelvic arterial blood flow in fetuses with SUA increases as pregnancy progresses, consistent with decreasing vascular resistance in the placenta and increasing resistance in the lower extremities.