Ultrasound pulsed Doppler studies of the uteroplacental circulation: the influence of sampling site and placenta implantation.

The results of Doppler ultrasound studies on the uteroplacental circulation show considerable variations which might be well explained by differences in methods. Using pulsed wave Doppler ultrasound, we studied the uteroplacental circulation in 45 normal pregnancies. Flow velocity waveforms were obtained at three different sampling sites: in the uterine artery near its origin, near the crossing with the external iliac artery and in arcuate arteries near the placenta bed. Significantly lower pulsatility index (PI) values were found in the arcuate arteries near the placenta bed compared to the uterine artery at the point where it crosses the external iliac artery. Between the origin and the crossing site of the uterine artery, no significant difference was found. The influence of placental site upon the PI in uterine arteries near the crossing was investigated longitudinally in 18 normal pregnancies. Lower PI values were found in uterine arteries near the placental site only at 16 and 20 weeks of gestation.