Reference ranges for flow velocities and the indices of the ductus venosus in low-risk pregnancies

Ductus venosus blood flow velocity measurements are mandatory in many clinical indications. The evaluation of the flow is performed either by comparing results with general reference tables or by qualitative assessment of the “a” flow, in regard to reversed or absent flow in the spectral waveforms. The aim was to develop normal reference ranges in low-risk pregnancies in our population.

Measurements of flow velocities (S, v, D, a) and indices (pulsatility index for veins, peak velocity index for veins, a/S, S/a) were performed by a single experienced specialist in 1279 singleton, uncomplicated pregnancies between 11 and 40 weeks gestation. The absolute flow velocities (S, v, D, a, VmPeak) and indices were obtained from spectral waveforms using the equipment producer’s inbuilt system. The still images were stored in the picture archiving and communication system.

The predicted reference ranges of the ductus venosus blood flow velocities according to the gestational age are shown in tables and graphics. Predicted reference curves based on the 5^th and 95^th percentiles according to gestational week were plotted and are given in tables and figures.

Normal reference ranges for absolute flow velocities and indices were calculated from a population of uncomplicated pregnancies attending a tertiary care center. The measurements were made from both the classic patterns of the waveforms and also considered variants of the spectral waveforms, which have recently been reported, for the first time in the medical literature.