The Single Umbilical Artery: Worth Evaluating or Better Left Alone?
ABSTRACT & COMMENTARY
Synopsis: On the basis of 37 published studies, there is little evidence to support a recommendation to pursue imaging or other studies in an infant found to have a single umbilical artery.
Source: Thummala MR, et al. Isolated single umbilical artery anomaly and the risk for congenital malformations: A meta-analysis. J Pediatr Surg 1998;33:580-585.
A literature search yielded 37 english language publications from 1952-1995, which addressed single umbilical artery (SUA) and associated anomalies. Eleven papers dealt with fetuses studies following stillbirth or abortion and 26 considered live-born infants who were either evaluated clinically for SUA or had the umbilical cord sectioned and examined microscopically. Not surprisingly, the incidence of SUA and other anomalies was significantly lower in the studies comprised of live infants. There was a great deal of variability among studies with the mean incidence of SUA in live infants being 0.55% (range 0.2-2.02%). The incidence of any associated malformation also varied widely with a mean of 27% (range 8.7-66.7%). Eleven percent had major anomalies, also with a wide range of 9-50% among studies. Only a limited number of children (204) underwent urologic/renal imaging evaluation. Of these, 16% were abnormal, and, in about half of these, the problem was "major."
Thummala and associates cite as major concerns precluding any definite recommendation for evaluation of a baby with SUA: 1) the large variability in incidence among studies, 2) the substantial costs related to finding a malformation (e.g., using ultrasonography it would cost $14,000-15,000 to identify one renal abnormality), and 3) difficulty in assessing the benefits of discovering an abnormality earlier as a result of extensive screening. They point out that recognition of SUA is also subject to great variation. For example, one in four SUAs may be missed if the determination is by clinical examination only. Furthermore, published studies did not generally have control groups, so the incidence of associated abnormalities could not be compared to the general population. Based on these concerns, Thummala et al conclude that, even though there is a mildly increased risk of renal anomalies with SUA, investigation is not warranted.
COMMENT BY THOMAS KENNEDY, MD, FAAP
Early in the first year of our residencies, we were taught to look for the presence of a single umbilical artery when doing the initial physical examination on a newborn infant. Depending on which study our faculty had read, finding an SUA was considered either a mild or significant risk for an associated, often renal anomaly. I recall a certain hedge: if we found only one artery, we were told not necessarily to begin an evaluation, but to merely make a note of it. This caused a certain uneasiness, since we knew SUA is frequently a part of major congenital malformation syndromes (for example, SUA is common with Trisomy 18). It was one thing to recognize a visible abnormality such as a cleft lip or palate, but what about a major, unseen renal problem like hypoplasia? It would have been comforting for us to know then that the analysis of all the published studies revealed only one instance of renal hypoplasia associated with SUA. Of the major genitourinary abnormalities associated with SUA in the combined studies, one-half were vesicoureteral reflux. Still, the incidence of reflux was low in infants with SUA who were evaluated by cystogram (about 2% with the incidence in the general population of newborns estimated at about 1%). Remember also that the incidence of renal anomalies in the general population is generally estimated to be 10%.
Furthermore, as Thummala et al point out, the incidence of associated congenital abnormalities in children with congenital heart disease is approximately 20-30% (renal abnormalities 12%), and we do not recommend imaging or extensively screening these infants. Thus, I believe we can reasonably maintain the approach of examining the umbilical cord for two arteries and a vein, documenting if there is just one artery, but not proceeding further with diagnostic studies of the GU tract.
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