Normal reference values of the pulsatility index from the uterine and umbilical arteries during pregnancy

To establish the normal reference values of the pulsatility index in the uterine (UtA PI) and umbilical (UmA PI) arteries during pregnancy. A total of 2081 normal pregnancies with normal growth fetuses were evaluated with pulsed Doppler ultrasound (US) between 20 and 40 weeks of gestation (WG). Both, UtA and UmA, were located with color Doppler US and PI measured in 5 consecutive and uniform cardiac cycles. In the uterine arteries, mean PI from the left and right arteries (Mean UtAPI) was calculated and the prevalence of unilateral or bilateral "notch" documented. Normal reference values for each gestational week were constructed, and reproducibility analyzed. There was a negative correlation between the gestational age and PI values from both arteries (Mean UtAPI = 1.57 + -0.02 X WG, r2= 0.07; PI UmA = 1.56 + -0.02 X WG, r2= 0.15). The prevalence of unilateral and bilateral "notch" in the uterine arteries was (median) 5% (range 3-10%), and 17% (range 4-23%), respectively. Reproducibility analysis for calculation of the Mean UtAPI showed an intraclass and interclass correlation coefficients of 0.87 (95% confidence intervals [CI] 0.74 - 0.93) and 0.78 (95% CI 0.59-0.88), respectively, and for UmAPI, 0.97 (95% CI 0.93-0.98) and 0.94 (95% Cl 0.88-0.97), respectively. Agreement analysis between observers for the calculation of the Mean UtAPI showed a mean difference of 0.01 (SD, 0.13) (95% limits of agreement [95% LA] -0.27-0.28) and for the UmAPI mean difference of 0.04 (SD 0.16) (95% LA, -0.29 - 0.36). The reference values here obtained of the mean UtA PI and UmAPI can be applied in the clinical surveillance of normal and complicated pregnancies.