LONGITUDINAL EVALUATION OF UTEROPLACENTAL AND UMBILICAL BLOOD-FLOW CHANGES IN NORMAL EARLY-PREGNANCY

The hemodynamic changes in the uteroplacental circulation and the umbi lical artery were evaluated in normal pregnancy from 8 to 14 weeks' ge station. A 6-9-MHz broad-band transvaginal sonographic transducer comb ined with pulsed color Doppler was used to scan 37 healthy volunteer p regnant women at weekly intervals. Vascular impedance to blood flow in all examined vessels decreased significantly throughout the first ges tational trimester. Resistance to pow was highest in the main uterine artery and decreased towards the spiral artery. When the flow velocity waveform patterns of the arteries under investigation were analyzed, specific changes were observed. The diastolic notch was present in the spiral artery flow velocity waveform in all cases until 10 weeks' ges tation. From then, the diastolic notch disappeared progressively and w as absent in 100% of cases at 13 weeks. The diastolic notch in the arc uate artery disappeared within 2 weeks of its disappearance in the spi ral artery. We could not detect intervillous blood flow during the fir st 12 weeks. From then on, intervillous pow was observed in most pregn ancies, reaching 100% at 14 weeks' gestation. These changes reflect th e growth and development of the uteroplacental circulation. The absenc e of detectable intervillous Pow during most of the first trimester co nfirms the concept that, during the first 3 months of gestation, blood flow to the intervillous space is inhibited by trophoblastic plugs.