Umbilical venous pressure is unaltered by severe, early-onset growth restriction

To determine whether severe, early-onset intrauterine growth restriction (IUGR) is associated with abnormal umbilical venous pressure (UVP) secondary to increased placental impedance.

42 singleton fetuses underwent fetal blood sampling from the umbilical vein during evaluation for severe, early-onset IUGR (diagnosed < 32 weeks or symmetrical IUGR diagnosed at any time in gestation). IUGR was confirmed at delivery. The UVP was measured with a solid-state transducer and corrected for amniotic fluid pressure. The ultimate cause of IUGR assigned was based on the antenatal laboratory and postnatal findings. Seven fetuses had a chromosome abnormality, 4 congenital viral infection, 8 miscellaneous causes and 23, by exclusion, uteroplacental (UP) dysfunction. Procedures complicated by fetal bradycardia were excluded because bradycardia raises the UVP.

The mean gestation was 31.4 weeks (range 23-38). The umbilical artery resistance index (UA RI) was significantly higher in fetuses with IUGR secondary to either UP dysfunction or a chromosome abnormality compared to the remaining categories of IUGR. The UVP fell outside the 95% confidence interval in only 3 fetuses - 2 with aneuploidy (a 1:7 translocation with a normal UA RI and a mosaic trisomy 21), and 1 with UP dysfunction. The UVP rose with advancing gestation independent of the underlying cause of IUGR. There was an inverse relationship between UVP and the UA RI independent of gestation (r2 = 0.08, p < 0.05). There was an inverse relationship between the UA RI and both the UV pH and PO2 in the fetuses with UP dysfunction. However, there was no relationship between the UVP and either UVpH, UVPCO2, or UVpO2.

These findings indicate that placental impedance has little clinically relevant impact on the UVP.