Umbilical blood flow velocity waveforms in different maternal positions and with epidural analgesia.

Umbilical blood flow velocity waves were measured in the fetuses of healthy parturients in early active labor to assess the influence of different maternal positions (N = 16) and of epidural analgesia (N = 16). The ratio of systolic peak to diastolic trough (S/D) of the umbilical blood flow velocity wave is reflective of vascular resistance distal to the point of measurement on the fetal side of the placenta. Umbilical blood flow velocity wave S/D ratios were significantly higher in the supine than in either lateral position indicating that umbilical artery vascular resistance is increased when the mother lies supine. After epidural blockade, the S/D ratios were unchanged in three and lowered to varying degrees in 13 parturients indicating that this method of pain relief beneficially affects umbilical artery vascular resistance.