Management of Pregnancy Complicated by Single Umbilical Artery

Mary King, MD; Peter S. Bernstein, MD, MPH; Mary King, MD, and Peter S. Bernstein, MD, MPH

Disclosures

May 01, 2006

Question

A patient is diagnosed with 2-vessel cord during 14 weeks of gestation. Would a repeat Doppler ultrasound help in confirmation? If yes, then when should we repeat it? What type of specific congenital anomalies have been reported so far?

Khalid Malik, MD, MBA

Response from Mary King, MD; Peter S. Bernstein, MD, MPH and Mary King, MD, and Peter S. Bernstein, MD, MPH

In the normal umbilical cord, there are 2 arteries and 1 vein. However, the variant with a single umbilical artery (SUA) and 1 umbilical vein is among the more common abnormal findings on fetal ultrasound examinations. The etiology of SUA is thought to be multifactorial, resulting either from aplasia or atrophy of the second umbilical artery or from persistence of the normally transient early embryonic SUA.[1] This condition can be identified in 1 of 2 ways: by visualizing a cross-section of the umbilical cord and noting the number of vessels, or by visualizing the umbilical vessels as they course around the fetal bladder. This should be apparent by the time the level II ultrasound is performed, typically between 18 and 22 weeks. The incidence of SUA has been reported to be anywhere from 0.2% to 1.6% among euploid fetuses and from 9% to 11% among aneuploid fetuses.[2] This number varies so much because of differences in sample size and populations sampled. A high incidence of SUA is also found when looking at a group of aborted or stillborn fetuses.

There is concern over SUA because of a reported association with both congenital anomalies and abnormal fetal growth, resulting in either intrauterine growth restriction (IUGR) or small for gestational age (SGA) infants. The correlation between SUA and congenital anomalies was noted as early as 1960.[3] The best data, however, come from a 1998 meta-analysis of 37 reported studies.[1] The authors recognized that this information comes from 2 types of studies: those that collected data from pregnancy losses, abortuses, and stillborn fetuses, and those that collected data from live-born fetuses. Among the first group, they found an SUA incidence of 2.1% and a rate of congenital malformations of 66.3%. In the second group of live-born fetuses, they found an SUA of 0.55% and a congenital malformation rate of 27%. This malformation rate is considerably above the baseline rate of 2% to 3%. There is widespread agreement on the need for a detailed anatomic survey to identify any other fetal anomalies once an SUA has been noted. The fetus must be carefully evaluated for any stigmata of aneuploidy, and a karyotype should be offered if these are found. Amniocentesis is also recommended if congenital anomalies are found in association with SUA.

The risk for IUGR is also of concern. A 1995 study[4] noted that IUGR was observed in 15% to 18% of cases with SUA, which is above the expected baseline rate of 10%. An earlier report also found that 22% of fetuses with SUA were SGA.[5] However, a 2005 trial[1] was unable to confirm these results, although this study was underpowered to detect a difference in IUGR/SGA rates between the SUA group and controls. In the absence of data to the contrary, it would seem prudent to obtain a third-trimester ultrasound for fetal growth and to initiate fetal testing if the growth is not appropriate.

Congenital malformations in many systems have been reported in association with SUA, but there is no specific pattern of malformations associated with SUA. Genitourinary and cardiac malformations are of particular concern, however. In the 1998 meta-analysis,[1] renal abnormalities were the most common, accounting for 16% of the total, although half of these were minor or self-limiting. The perception that renal abnormalities are particularly common has led some to recommend a postnatal renal evaluation for all infants with SUA, but the best evidence is that the cost-benefit ratio does not favor this approach.[2] However, a careful neonatal examination is essential. A report on the usefulness of fetal echocardiography once SUA has been identified was recently published.[6] In this study, fetal echocardiograms were performed on 103 of 127 patients with isolated SUA, and all of the studies yielded normal results. Only 1 fetus in this group had congenital cardiac disease, which was not detected. It is important to keep in mind, though, that all fetuses in this study were first evaluated with a level II ultrasound that included visualization of a 4-chamber view of the heart as well as outflow tracts. The authors detected congenital cardiac disease in many fetuses on the initial study but did not find that the more detailed cardiac examination added anything to their evaluation.[6]

There is also the question of the confidence with which the diagnosis of SUA is made. A recent series reported a positive predictive value of 88.4% among fetuses noted to have this finding on ultrasound. This group prenatally identified 141 patients with SUA, but 11 (12.2%) of these were in fact shown to have a normal 3-vessel cord at delivery. There is also a report indicating that some SUAs may be missed on screening ultrasound and that sensitivity for identification of SUA is 65%.[7] Much of the data on SUA come from older publications, and the sensitivity of today's screening ultrasound may be better than what is reported in the literature. In addition, the same report[7] commented that clinical evaluation may also be flawed; in this study, obstetricians missed 24% of SUAs and pediatricians missed 16%.

When managing a pregnancy complicated by SUA, it is essential to obtain a thorough ultrasound examination to look for any associated anomalies or evidence of aneuploidy. If none is found, then the fetus is presumed to have isolated SUA. Most authors do not recommend amniocentesis in this situation, although there is still an increased risk of congenital malformations and chromosomal abnormalities. Patient counseling is important here -- it is impossible to be completely certain that the fetus has no malformations even if none is seen on ultrasound. Fetal echocardiography does not seem to contribute significantly to the evaluation of these fetuses, assuming that they have normal 4-chamber views and outflow tracts. A third-trimester assessment of fetal growth is warranted and a careful evaluation of the newborn is necessary. Routine renal imaging is not justified by the current data; however, follow-up of any abnormal findings is appropriate.

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