Abstract
Evaluation of the umbilical cord is an important part of a fetal ultrasound examination. The gold standard for documenting the umbilical cord has been an axial section of a free loop of umbilical cord within the amniotic fluid. There are normally two umbilical arteries and one umbilical vein, but in approximately 1% of pregnancies, only one umbilical artery is present. The presence of a two vessel umbilical cord or a single umbilical artery has been associated with an increase in other fetal abnormalities. When axial views of the umbilical cord are not obtainable, it is common practice to use color Doppler to determine the presence or absence of the umbilical arteries as they course adjacent to the fetal bladder. The three-vessel cord is confirmed by identifying the right and left umbilical arteries on each side of the bladder.
This study compared axial views of free-floating two vessel umbilical cords with color Doppler evaluation of the umbilical arteries adjacent to the bladder and attempted to answer three questions regarding the single umbilical artery: 1) Does the presence of two umbilical arteries next to the fetal urinary bladder validate the documentation of a three vessel umbilical cord; 2) When one umbilical artery was absent, was there a prevalence as to which side was affected; and 3) Does the side of the absent umbilical artery correlate with an increase or decrease in risk for other anomalies?
This study showed that there were three sonographic variations with respect to a two vessel umbilical cord when axial gray scale images of the umbilical cord were compared with color Doppler images of the umbilical arteries adjacent to the fetal urinary bladder. The most prevalent variation, occurring in 17 (49%) of 35 cases, was the two-vessel cord with the left umbilical artery absent. The right umbilical artery was absent in 13 (37%) of 35 cases. The third and least prevalent variation, occurring in five (14%) of 35 cases, was a two vessel umbilical cord with both umbilical arteries present adjacent to the fetal urinary bladder. Each of the single umbilical artery variations in the study were associated equally with other sonographically identifiable abnormalities. We conclude that a two vessel umbilical cord may be missed by relying solely on color Doppler views of the umbilical arteries adjacent to the bladder.