Doppler analysis of the umbilical artery. The importance of choosing the placental end of the cord.

Thirty normal pregnancies were studied with continuous or pulsed Doppler ultrasound (50 measurements). The ratio of systolic (S) to end-diastolic (D) measurement, or S/D ratio, was obtained at both ends of the cord: the placental insertion and the fetal abdominal insertion. A statistically significant difference was demonstrated between the two sets of measurements. Normal values were obtained at the placental insertion, whereas, simultaneously, the fetal abdominal insertion generated highly abnormal values. When performing Doppler waveform analysis of the umbilical artery, if abnormal values are obtained, one should be cautious to be certain that they originated from the placental insertion.