The role of umbilical vein blood flow assessment in the prediction of fetal growth velocity and adverse outcome: a prospective observational cohort study

Background: Identifying fetal growth restriction and distinguishing it from a constitutionally small fetus can be challenging. The umbilical vein blood flow is a surrogate parameter of the amount of oxygen and nutrients delivered to the fetus, providing valuable insights about the function of the placenta. Nevertheless, currently, this parameter is not used in the diagnosis and management of fetal growth restriction. Objectives: To evaluate the umbilical vein blood flow and fetal growth velocity in small for gestational age fetuses and in fetal growth restriction, and to evaluate their capacity to predict adverse perinatal outcome and iatrogenic preterm birth. Secondly, to assess the correlation between umbilical vein blood flow and fetal growth velocity. Study design: This was a prospective multicentric observational cohort study of women with a diagnosis of small for gestational age or fetal growth restriction in which fetal biometry and Doppler assessment, including umbilical vein blood flow measurement, were performed. The fetal growth velocity was derived from the difference between the estimated fetal weight calculated in two consecutive sonographic evaluations. The pregnancies were followed until delivery. Between-group differences were evaluated, and Pearson or Spearman correlation coefficients were reported to assess the relationship between variables of interest. Optimal cut-offs on the resulting receiver operating characteristic curve were determined and used to predict the outcomes of interest. Simple and multiple logistic regression models were estimated using umbilical vein blood flow and fetal growth velocity to predict adverse perinatal outcomes and iatrogenic preterm birth. Results: The study population included 64 small for gestational age and 58 growth restricted fetuses. When compared to reference ranges, small for gestational age fetuses had significantly lower fetal growth velocity and umbilical vein blood flow (p<0.001). When compared to small for gestational age, fetuses with growth restriction had lower umbilical vein blood flow (p<0.001), umbilical vein blood flow corrected for estimated fetal weight and abdominal circumference (p<0.01 and p<0.001), and fetal growth velocity (p<0.001). Fetal growth velocity was positively correlated with umbilical vein blood flow (r=0.46, p<0.001). The multivariable logistic regression analyses showed that, after adjusting for diagnosis of fetal growth restriction, umbilical vein blood flow ≤0.65 MoM (adjusted odds ratio [aOR] 3.5; 95%CI 1.0-11.8) and fetal growth velocity ≤0.63 MoM (aOR 3.0, 95%CI 1.2-7.9) were associated with adverse perinatal outcome. Furthermore, when accounting for fetal growth restriction diagnosis, umbilical vein blood flow ≤0.60 MoM (aOR 5.2, 95%CI 1.7-15.9), and fetal growth velocity ≤0.63 MoM (aOR 3.6, 95%CI 1.1-12.6) were significant predictors of iatrogenic preterm birth. Conclusions: Umbilical vein blood flow could play a role to identify fetuses with fetal growth restriction and to predict fetal growth at the subsequent biometric evaluation. We found a significant correlation between umbilical vein blood flow and fetal growth. Umbilical vein blood flow and fetal growth velocity are independent predictors of iatrogenic preterm birth and adverse perinatal outcome in a population of small fetuses, regardless of the Delphi consensus criteria. These results support future study on the predictive value of this parameter in fetuses with a suspected fetal growth restriction.