Validation study of the capacity of the reference curves of ultrasonographic measurements of the umbilical cord to identify deviations in estimated fetal weight

Background. The objective of this study was to evaluate the capacity of the cross-sectional area and diameter of the umbilical cord, and the area of Wharton's jelly (WJ), to predict abnormalities in estimated fetal weight (EFW) in 20-40 week, low-risk pregnancies. Methods. A validation study was performed in 1,828 pregnant women. Fetal weight was estimated by ultrasonography and classified as: small for gestational age (SGA), appropriate for gestational age (AGA) or large for gestational age (LGA) according to the 10th and 90th percentiles of the reference curve. Measurements of the parameters of the cord were used to classify it as thin, normal or thick using the 10th and 90th percentiles of the reference curves as limits. The capacity of the diameter and total area of the cord and the area of WJ to predict abnormal EFW was calculated for different gestational ages. Results. The capacity of the diameter of thin cords to predict SGA fetuses (S =8.3%, PPV =16.5%) or thick cords to predict LGA fetuses (S =5.5%, PPV =30.1) was weak, similar to the capacity of the area of the umbilical cord to predict SGA (S =8.3%; PPV =16.3%) or LGA fetuses (S =5.5%; PPV =27.8%). The capacity of the area of WJ to predict SGA fetuses (S =5.7%, PPV =11.7%) was similar to its capacity to predict LGA fetuses (S =4%, PPV =27.1%). Conclusion. Despite the correlation between the diameter and cross-sectional area of the cord and EFW, these measurements were not found to be useful in predicting alterations in EFW and should not be used for this purpose.