The utility of umbilical venous flow volume in predicting birth weight in the human foetus

Background: The umbilical venous flow volume is a direct physiological representation of the amount of nutrients and oxygen reaching the foetus from the placenta. Although the umbilical venous flow volume is reported to be reduced in growth restricted foetuses, its association with neonatal birth weight has never been examined in normal human pregnancies. Methods: In a prospective, longitudinal ultrasound study of 136 low risk singleton pregnancies in Western Australia, the umbilical venous blood flow volume was calculated three times in pregnancy (18, 26 and 34 weeks gestation) using Doppler ultrasound. The mean internal diameter of the umbilical vein and its mean flow velocity were used to calculate the flow volume using a validated formula. A series of general linear regression models were derived with neonatal birth weight as the dependant variable and umbilical venous flow volume at each gestation as the main predictor variable. Maternal BMI and gestation at birth were entered in the models as confounder variables. Results: Median maternal age was 30. The mean birth weight was 3475 grams (SD 490) with the mean gestation at birth of 38.9 weeks (SD 1.22).The umbilical venous blood flow volume was 28.7 ml/min (SD 10.3) at 18 weeks which increased to 131.5 ml/min (SD 38.1) at 26 weeks and 268.9 ml/min (SD 82.4) at 34 weeks gestations respectively. The umbilical venous flow volumes at 26 weeks (B-Coefficient 2.94, p-value 0.001) and at 34 weeks (B-Coefficient 1.69, p-value 0.000) were significant predictors of birth weight after controlling for maternal BMI and gestation at birth. Conclusion: The umbilical venous flow volume from 26 week gestation can act as a useful adjunctive tool in predicting foetal growth, as it is significantly associated with neonatal birth weight.