| pubmed-article:8365511 | pubmed:abstractText | A cross-sectional transvaginal color and pulsed Doppler study was performed on 95 normal singleton pregnancies to establish blood flow characteristics of maternal and placental components of circulation. During the pregnancy, vascular impedance to blood flow decreases from the main uterine artery to the spiral arteries in the maternal component of uteroplacental circulation. In the placental component of circulation, vascular impedance decreases from the umbilical artery to the fetal arteries within placenta-intraplacental arterioles. At the same time, in both components of uteroplacental circulation, an increase of blood flow velocity with gestational aging was observed. There was no significant drop of vascular impedance of blood flow or increase of blood flow velocity around the 12th or 14th gestational week, which should prove the hypothesis of 'opening' of spiral arteries which have tips plugged with trophoblast tissue. | lld:pubmed |
