Analysis of umbilical artery flow parameters during fetal variable decelerations using computerized Doppler waveforms.

Umbilical artery velocity waves were obtained by Doppler ultrasonography before, during, and after 20 episodes of fetal heart rate (FHR) variable decelerations (VD) during the active stage of labor in 8 women. During 50% of the VD periods, the umbilical artery resistance flow parameters increased significantly (p < 0.01). The increase in resistance preceded the decrease in FHR in six episodes (30%) of VD (AR-VD group; arterial resistance VD) and did not precede the change in FHR in another ten episodes (50%) of VD (VR-VD group; venous resistance VD). In the AR-VD group the FHR accelerations occurred before the decelerations in only 1 case (17%), while in the VR-VD group FHR accelerations preceded the decelerations in 8 out of the 10 episodes (80%). Using these Doppler studies, it may be possible to differentiate between two groups of VD: AR-VD - which are caused by umbilical artery occlusion and thus preceded by a measurable increase in umbilical artery resistance - and VR-VD - which are not preceded by a measurable increase in umbilical artery resistance and may be caused by fetal hypoxia.