Umbilical artery time-averaged maximum velocity: First trimester reference range

We previously showed that the umbilical artery (UA) time-averaged maximum velocity (TAMXV) measured within the first trimester seems to be a “Marker” of utero-placental development as it correlated with uterine artery pulsatility index. Aim of our study was to construct a reference range for TAMXV for first trimester.

Women with Doppler of the UA blood flow velocity waveforms in the first trimester were included. To create the reference range we based on the model of Royston and Wright, assuming that at each gestational age (GA) the measurement has a Gaussian distribution with mean and standard deviation (SD) and that both vary with GA. Centile curve was calculated centile = mean+KxSD. Polynomial regression analysis, Spearman rank test and Mann-Whitney were used for statistical analysis. A p < 0.05 was considered significant.

Fourteen (12%) women developed preeclampsia and twelve (10.3%) small for gestational age (SGA). The polynomial regression that best fitted our measurements was: y =-15.26+1.946*x (x = gestational age). The SD, the 10th and 90th percentile were calculated, SD =-0.4069+0.2161*x, mean ± 1.6453xSD. TAMXV shows a consistent (r = 60; p < 0.0001), linear increase with advancing GA. To compare cases, with PE with those with an SGA, a ratio between the observed and expected mean TAMXV for GA was calculated. Women, with PE, had a lower O/E-ratio than those with SGA (PE 0.89 ± 0.23 vs. SGA 1.04 ± 0.21; p = 0.06).

A reference range for the TMAXV in the first trimester has been generated. Its general use in the low risk population has to be validated. At risk women with PE seem to have lower TAMXV values. More data need to confirm this observation.