Single umbilical artery (SUA)

Single umbilical artery (SUA)


The umbilical cord is the tube-like structure that connects the baby at the abdomen to  the placenta (and mother). The umbilical cord usually contains three blood vessels ; a single vein and 2 arteries ( a 3 vessel cord) . The vein carries blood rich in oxygen and nutrients from the placenta to the fetus. The arteries carry oxygen poor blood and waste products from the fetus to the placenta.


Occasionally, one artery wastes away or fails to develop leaving only a single umbilical artery (a two vessel umbilical cord). A single umbilical artery (SUA) is seen in 0.2% to 1% of pregnancies [1-3]. SUA is reported to be more common in twin pregnancies and in placentas where the umbilical cord is at the edge of the placenta[3].

Evaluation of SUA

Although SUA may occur alone (isolated) in some cases, SUA may be associated with a collection of other findings that suggest a specific disorder (syndrome). When SUA is found on an ultrasound examination a search for abnormalities of the heart, gastrointestinal tract, brain, urinary tract, and bones will usually be performed to evaluate the baby for other possible abnormalities [4-7].

If additional abnormalities are found there may be as high as a 50% chance that the baby has a chromosomal abnormality including trisomy 13 or trisomy 18 [10]. Another condition that has been associated frequently with SUA is VATER association (vertebral defects, anal atresia, tracheoesophageal fistula with esophageal atresia, and radial dysplasia). Down syndrome has not commonly been associated with SUA [5,8-10]

If SUA is the only finding and there are no other findings on ultrasound examination the risk of a chromosomal abnormality appears to be very low (0 to 2.6%) [8,10-12]. Nonetheless an amniocentesis may sometimes be offered for further evaluation, since additional findings in some syndromes may go undetected until after delivery [5,6].


In the past SUA was reported to be  associated with  with low birthweight [2,5,11,14-16], and an increased risk for stillbirth [11,12,7], for that reason evaluation of the baby's growth and well being during the last 3 months of pregnancy has been recommended,

More recent studies have shown that babies with isolated SUA do not appear to be at any greater risk for poor growth than the fetus with a normal three vessel umbilical cord [17-19]. In addition, one large study of 255 patients with SUA did not find an increased risk for stillbirth in fetuses with SUA.  However, this study was not able to determine if serial testing might have been responsible for preventing  potential stillbirths and the reduced rate of stillbirths in the fetuses with SUA .


While awaiting spontaneous labor at term, the planned method of delivery is  usually vaginal, with cesarean delivery performed for routine obstetric indications. If other significant structural malformations are present,it is sensible for the infant to  be delivered in a hospital with a neonatal intensive care unit (NICU).

After Delivery

One study reported an increased rate of inguinal hernias, a condition where part of the intestine bulges through a weakness in the groin area, in newborns with SUA [14]. Aside from a thorough examination of the infant no special studies appear to be  warranted in infants with isolated SUA [20].


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