Single Umbilical Artery: Need for Specialist Fetal Echocardiography

Abstract & Commentary

By John C. Hobbins, MD, Professor, Department of Obstetrics and Gynecology, University of Colorado Health Sciences Center, Denver, is Associate Editor for OB/GYN Clinical Alert.

Synopsis: A large study involving fetuses with single umbilical artery shows that few serious cardiac anomalies are missed with standard four-chamber and outflow tract views, when no extra cardiac abnormalities are noted.

Source: DeFigueiredo D, et al. Isolated single umbilical artery: Need for specialist fetal echocardiography? Ultrasound Obstet Gynecol 2010;36:553-555.

A Single Umbilical Artery (SUA) is found in about 1 in 200 fetuses in the second trimester. Since the finding is associated with an increase in fetal anomalies, it alerts clinicians to search for any of the possible abnormalities linked with this finding. However, opinions vary as to how this search should be conducted.

In an effort to help develop a common diagnostic approach, investigators from London tackled one option — the need for a full fetal echocardiogram. They reviewed data from 46,272 patients who had routine second trimester ultrasound evaluations, which included a four-chamber view of the fetal heart, along with an attempt to image the outflow tracts. Each patient in the study had a fetal anatomic survey between 18 and 25 weeks, at which time an SUA was found in 264 cases (0.5%). In 233 patients, no cardiac defects or other anomalies were noted, but two of the "cleared" fetuses were found later to have ventricular septal defects (VSD). In the second group of 10 patients, isolated cardiac abnormalities were identified in utero, and in the third group of 13, in whom extra cardiac anomalies were diagnosed, six also had cardiac defects. In total, the incidence of cardiac defects was 6.5%, which included 10 cases (4.3%) from the 233 patients in groups 1 and 2. Six of the 13 (46.2%) with extra cardiac anomalies also had cardiac defects. Most importantly, in 11 of the 16 patients delivering fetuses with cardiac defects, the diagnosis was made in utero with four-chamber and outflow views alone. The ones that slipped through were small VSDs and a persistent superior vena cava, anomalies that are of lesser consequence.

The authors' conclusion was that if four-chamber and outflow tracts appear normal, "it may not be necessary to refer patients (with SUA) for specialist fetal echocardio-graphy." However, if extra cardiac anomalies are found with SUA, there is about a 50% chance for an associated cardiac abnormality, and this would warrant a detailed cardiac examination.

Commentary

Our impression is that SUA is more common than the 0.5% incidence noted in the above paper. However, referral centers are often dealt loaded decks for obvious reasons. In fact, one center doing high-risk screening at 11-14 weeks noted an incidence of SUA in 5.9%,1 which undoubtedly reflects a mixture of structurally anomalous and chromosomally abnormal fetuses that do not make it to the second trimester sonogram because of spontaneous loss or termination of pregnancy. From data pooled from the literature involving 1038 patients with SUA and cited in the DeFigueiredo study, it is certainly clear that this finding is associated with a higher rate of fetal anomalies (33%) and, specifically, cardiac anomalies (11%). Hua et al found an incidence of SUA in the overall population of 0.6% and, in those with SUA, there was a 20-fold increased risk for cardiac anomalies, a three times greater chance of renal anomalies, and a two-fold risk of IUGR.2 Another important anomaly syndrome to be ruled out is trisomy 18, since about 50% of fetuses with this abnormality have SUAs.

Here are some suggestions for patients whose fetuses have SUA:

  1. When performing a second trimester anatomy scan, particular attention should be paid to the fetal spine, posterior fossa, and kidneys (pelvic kidneys are not an uncommon accompaniment to SUA).
  2. The four-chamber and outflow tracts should get the most attention.
  3. If quad screen results are available, the pattern of very low analytes should trigger a "marker" search for trisomy 18.
  4. If everything appears normal, there is no need for a full fetal echocardiogram.
  5. Another scan should be scheduled for after 30 weeks to check interval fetal growth.

Most importantly, normal results from steps 1-4 should be very reassuring for patients with a fetus with SUA, as the first thing they will do after learning of an SUA, will be to go online. There they will find a wealth of scary information.

References

  1. Rembouskos G, et al. Single umbilical artery at 11-14 weeks gestation: Relation to chromosomal defects. Ultrasound Obstet Gynecol 2003;22:567-570.
  2. Hua M, et al. Single umbilical artery and its associated findings. Obstet Gynecol 2010;115:930-934.