Reference ranges for uterine artery mean pulsatility index at 11-41 weeks of gestation

To construct gestational age (GA)-based reference ranges for the uterine artery (UtA) mean pulsatility index (PI) at 11-41 weeks of pregnancy.

A prospective cross-sectional observational study was carried out of 20 consecutive singleton pregnancies for each completed gestational week at 11-41 weeks. UtAs were examined by color and pulsed Doppler imaging, and the mean PI, as well as the presence or absence of a bilateral protodiastolic notch, were recorded. Polynomials were fitted by means of least-square regression to estimate the relationship between the mean UtA-PI and GA.

A total of 620 women were included. A second-degree polynomial (Log(e) mean UtA-PI = 1.39 - 0.012 x GA + GA(2) x 0.0000198, with GA measured in days), after a natural logarithmic transformation, was selected to model our data. There was a significant decrease in the mean UtA-PI between 11 weeks (mean PI, 1.79; 95(th) centile, 2.70) and 34 weeks (mean PI, 0.70; 95(th) centile, 0.99). It then became more stable up until 41 weeks (mean PI, 0.65; 95(th) centile, 0.89).

The mean UtA-PI shows a progressive decrease until the late stages of pregnancy. Reference ranges for mean UtA-PI may have clinical value in screening for placenta-associated diseases in the early stages of pregnancy, and in evaluating patients with pregnancy-induced hypertension and/or small-for-gestational age fetuses during the third trimester.