Umbilical artery pulsatility index: reliability at different sampling sites

To analyse the inter-observer and inter-artery reliability of the umbilical artery (UA) pulsatility index (PI) at different sampling sites.

One hundred consecutive singleton pregnancies between 24 and 40 weeks were included. The PI was calculated by two independent operators from both umbilical arteries at the placental end, at a free-floating loop and at the perivesical segment. Reliability analyses were performed between observers and between arteries at each sampling site.

The mean percentage of PI difference between arteries was 15.2, 14.5 and 22% at the placental end, free-loop and perivesical site, respectively. The Intraclass correlation coefficients at each site were 0.51, 0.59 and 0.67, respectively. Whereas about 20% of cases showed a percentage of PI difference between arteries greater than 20% at free-loop and placental end sites, and at the perivesical site this figure was 45%.

The perivesical sampling site for UA PI calculation is more reliable than at a free-floating loop, albeit without significance, and is significantly more reliable than at the placental end of the umbilical cord. Since discordances in PI between both arteries are more pronounced at the perivesical site, it seems mandatory to evaluate both arteries in this segment.