Prediction of SGA at Birth by Using the Right Portal Vein Diameter Measurement at the 30-35-Week Scan

This study sought to test the hypothesis that the measurement of the right portal vein (RPV) diameter on the transverse abdominal view at the 32-week ultrasound scan is small in fetuses with growth retardation and to validate the use of this measurement as a tool for detecting small for gestational age (SGA) at birth.

This was a retrospective cohort study at a single centre. The study population comprised 326 consecutive pregnancies, including 29 SGA at delivery and 297 unaffected cases. Stored images of the transverse view of the abdomen, obtained at the routine third trimester scan, were used to assess the diameters of the umbilical vein, the portal sinus, and the RPV.

The portal sinus and RPV diameter were smaller compared with the reference group (P = 0.021 and P < 0.001, respectively). Using a 10th percentile cut-off, the detection rate for SGA at birth was 38% for the RPV diameter versus 45% for the estimated fetal weight. The false-positive rates were 9% versus 8%, respectively. Multiple regression analysis revealed that RPV below the 10th percentile remained an independent four-fold risk factor for SGA (odds ratio [OR] 5.05; 95% confidence interval [CI] 1.94-13.14). Further analysis revealed a higher prevalence of induction of labour for non-reassuring fetal well-being (P = 0.005), fetal acidemia (P = 0.028), and admission to a neonatal intensive care unit (NICU, P = 0.029) in the RPV ≤10th percentile group.

RPV below the 10th percentile could be a reliable third trimester ultrasound marker of a subnormal fetal environment. This study proposed a new and accessible approach for prediction of SGA.