OP20.13: The shift of umbilical‐portal watershed in the growth‐restricted fetus assessed by velocity measurement in the left portal vein

Reversed flow in the left portal vein (LPV) has been suggested as a marker of placental compromise. We hypothesize that the time-averaged maximum flow velocity (TAMXV) in the LPV reflects the umbilical–portal distribution to the right lobe of the fetal liver, and aimed to assess this effect in fetal growth restriction (FGR). After informed written consent, 29 women with singleton pregnancies complicated by FGR (≤5 percentile) were examined using Doppler ultrasound to assess the TAMXV in the LPV and compared with the fraction of portal vein contribution to the right liver lobe (calculated from flow measurements in the portal stem and LPV). Velocities were measured at an insonation angle≤ 30° and diameters perpendicular to the vessel wall. TAMXV was measured in 28/29 (97%) of the cases. In 16/28 fetuses (57%) the umbilical artery (UA) pulsatility index (PI) was normal, in 11/28 (39%) the UA PI was > the 97.5 percentile, and in 1/28 (4%) there was absent end-diastolic flow in the UA. The TAMXV in the LPV was below the 50 percentile of the reference population in 25/28 FGR-fetuses (89%). In all 12 fetuses with UA PI > 97.5 percentile or absent end-diastolic flow in the UA, the TAMXV in the LPV was ≤ the 5 percentile of the reference population. Reversed flow in the LPV was observed in 2/28 fetuses (7%). When comparing TAMXV in LPV with the portal flow contribution, there was an inverse strong direct relationship. LPV flow velocity directly reflects the umbilical–portal venous distribution to the fetal liver, lower velocity signifying a shift of the watershed to the left. Such a shift probably reflects an adaptation to restricted placental resources making the measurement of TAMXV a potential useful clinical parameter and research tool.