Umbilical artery flow velocity waveforms and the placental vascular bed.

Umbilical artery Doppler studies were performed close to delivery in 17 women (seven with healthy pregnancies and 10 complicated by intrauterine growth retardation), and results were analyzed by calculating the pulsatility index. In each case the placenta was examined histologically, and the small arteries and arterioles were counted in the tertiary stem villi. A highly significant negative linear relationship was found between pulsatility index and mean small arterial vessel count per field (r = 0.71, p less than 0.01). This suggests that when the pulsatility index is raised (indicating increased resistance), one possible explanation may be obliteration of small placental arteries.