Objectives To assess the effect of audit and feedback on the performance of first-trimester uterine artery pulsatility index (UtA-PI)

Introduction: Uterine artery pulsatility index (PI) is a key variable in the first trimester screening for pre-eclampsia. The aims of the study were to examine the effect of sampling the uterine arteries at a site distal to the level of the internal os, and to determine a lower limit of peak systolic velocity (PSV) to establish an auditable standard. Material and Methods: PI and PSV measurements were performed at 11-13⁺⁶ weeks' gestation at two sites: at the level of the internal os and 3 cm distal to the internal os. Comparative analyses utilised the Student's paired t-test. A 90% reference interval of transformed PSV measurements at the internal os was generated by polynomial regression. Results: There was a significant reduction in both the PI (14.9%) and the PSV (17.4%) when measured at the distal site compared to the level of the internal os (both p < 0.001). The best estimated 5th centile for uterine artery PSV at 11-13⁺⁶ weeks was 60.9 cm/s. Conclusion: PI measurements performed distal to the internal os are significantly lower and will result in inaccurate pre-eclampsia risk assessment. PSV measurements below 60 cm/s are likely to indicate an incorrect sampling site. Development of auditable measurement standards is important to ensure accuracy of prospective pre-eclampsia screening.

Introduction: First-trimester uterine artery pulsatility index (PI) measurements form part of an algorithm used to assess the risk of developing pre-eclampsia. The objective of this study was to construct a population-specific reference range for both the lower and mean maternal uterine artery PI at 11-13⁺⁶ weeks' gestation and to assess measurement agreement. Materials and Methods: Reference ranges for mean and lower PI measurements were developed using polynomial regression models following prospective collection of maternal uterine artery PI measurements at 11-13⁺⁶ weeks' gestation. Measurement agreement studies were performed by two experienced operators. Results: Measurements from 298 women were included in the primary study. Polynomial regression indicated no change over gestational age for the lower PI (mean 1.44). There was an inverse relationship between the average PI and gestational age (mean [0.8960 + (2.9771 × CRL^-1/2)]²). PI measurement agreement was good-strong (intraclass correlation (ICC) 0.50-0.79) between operators, and within-operator agreement was almost perfect (ICC 0.88-0.93). Conclusions: Reference ranges for both the average and lowest PI of the maternal uterine arteries were derived at 11-13⁺⁶ weeks' gestation. This will provide a basis for development of auditable standards for first-trimester uterine artery Doppler measurements. The PI measurements are reproducible and reliable.