Fetal blood velocity waveforms in 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 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.