Continuous wave Doppler ultrasound was used together with B-mode real time ultrasound to study feto-placental blood flow in utero. The results of 887 examinations on 221 patients are presented. The fetal heart rate acceleration slope and pulsatility index (P.I.) of the audiofrequency ultrasound display were analysed. There was a significant reduction in fetal heart rate (P less than 0.001) and P.I. (P less than 0.001) with advancing gestational age in normal pregnancy. In contrast, in retarded intrauterine growth a significant increase in P.I. values was observed in 77% of patients.

SummaryA combination of pulsed echo and continuous wave Doppler ultrasound was used to obtain blood flow velocity signals from the umbilical arteries of 10 patients during uncomplicated spontaneous labour. Audio frequency analysis of these signals yielded fetal blood velocity waveforms. Analysis of these waveforms demonstrated that placental vascular resistance to feto‐placental blood flow is not altered by uterine contractions, artificial rupture of the membranes, the infusion of oxytocin nor the administration of analgesia during uncomplicated labour.

A combination of pulsed echo and continuous wave Doppler ultrasound was used to obtain blood flow velocity signals from the umbilical arteries of 18 normal patients from the 16th until the 40th week of pregnancy. Audio frequency analysis of these signals yielded fetal blood velocity waveforms. Analysis of these waveforms demonstrated that the placenta is an organ of low vascular resistance and that placental resistance to blood flow declines with advancing gestational age in normal pregnancy.