DOPPLER ULTRASOUND OF THE UTEROPLACENTAL AND FETOPLACENTAL CIRCULATIONS - PLACENTAL LOCATION, NORMAL VALUES AND REFERENCE CURVES

Aim: Doppler ultrasound assessment of blood flow velocity waveforms fr om the maternal and fetal sides of the placenta in normal pregnancies, taking into consideration placental location, in order to establish n ormal values and reference curves. Method: A cross sectional study of uneventful singleton pregnancies with gestational ages from 18 to 41 w eeks and later on healthy newborns was performed by continuous-wave-Do ppler ultrasound. Doppler flow signals from the uterine artery or the corresponding ascending branch and the umbilical arteries were analyse d using the resistance index RI. The RI-values from the uterine circul ation were classified according to the proximity of the placenta. Norm al values and reference curves were established on the basis of centil es. Results: After consideration of exclusion criteria, 757 pregnancie s remained for evaluation. The resistance index reference curves of th e uterine circulation were dependent on placental location, with proxi mal RI-values being lower, but with nearly constant course during the second half of pregnancy. In contrast, the umbilical artery RI-values were higher but showed a continuous decrease. Conclusion: In the secon d half of pregnancy, down stream flow resistance of the uterine circul ation is very low and nearly constant but depends on placental locatio n. The fetoplacental circulation shows high flow resistances which dec rease with increasing gestational age. These reference curves are comp arable with others where placental location is taken into consideratio n.