Uterine artery pulsatility index in the first trimester: assessment of intersonographer and intersampling site measurement differences.

OBJECTIVE

To determine intersonographer, intersampling site pulsatility index differences in the ascending branch of the uterine artery (UtA-PI) and their effect on detection rates (DR) for early onset preeclampsia (PE).

METHODS

A prospective observational study was conducted including 52 women with singleton viable pregnancy at 11-13 weeks' gestation. Consecutive bilateral UtA-PI measurements were performed by two sonographers. Both sonographers hold the Fetal Medicine Foundation (FMF) uterine artery Doppler assessment competency certificates. Sonographer "A" underwent mentorship-based specialist training at the FMF; whilst sonographer "B" is a fetal maternal specialist who was deemed competent to measure UtA-PI based on completion of the FMF online course. Both sonographers were unaware of each other's UtA-PI and peak systolic velocity (PSV) measurements throughout the study. UtA-PI was measured by sonographer "A" at 1, 2 and 3 cm distally from the internal os. UtA-PI minimum ("Low-PI") and mean ("Mean-PI") were determined. Intraclass correlation (ICC), Bland-Altman analysis and Wilcoxon signed rank test were performed to determine bias, 95% limits of agreement (LOA) for intersonographer and intersampling site differences. Simulation studies were performed to determine the effect on early onset PE screening DR.

RESULTS

(1) Intersite assessment indicated that UtA-PI and PSV decreased by 7-8% per centimeter relative to the measurement taken at the internal os; (2) Sonographer "B" UtA-PI measurements were significantly lower than those of sonographer "A" for "Low-PI" (p = .001), "Mean-PI" (p = .002) and PSV (p = .004) determined by Wilcoxon signed rank test. The mean reduction in "Low-PI", "Mean-PI" and PSV of sonographer "B" relative to sonographer "A" were 14.04%, 11.09% and 10.99%, respectively; (3) Measurements taken by sonographer "B" at the level of the internal os were comparable to measurements taken by sonographer "A" at 2 cm distal to the internal os (low-PI: p = .98, Mean-PI: p = .49 and PSV: p = .24); (4) Between sonographer ICC for UtA-PI was asymmetrical strong (left ICC = 0.72, 95%CI: 0.51-0.84) to fair (right ICC = 0.38, 95%CI: -0.08-0.64); and (5) The 14% mean intersonographer difference in lowest UtA-PI would have resulted in an 7% difference in PE screening performance.

CONCLUSIONS

The measurement of UtA-PI is sampling site dependent with the potential for significant intersonographer differences despite the availability of a prescriptive measurement protocol. This is an important observation as it implies that sonographer "B" inadvertently measured the UtA-PI at a distal site, not at the level of internal os, compared to those measured by sonographer "A", resulting in a lower DR for early onset PE.