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You are the paediatric house officer performing discharge examinations on the postnatal ward. You are informed of this term neonate whose umbilical cord was noted to have a single umbilical artery (SUA) at delivery. He is otherwise well. You cannot detect any abnormalities on physical examination. Historically, SUA has been said to be associated with congenital malformations of different organ systems. You wish to appraise the evidence whether or not this infant needs investigations to detect associated malformations.
Structured clinical question
In a term neonate with no other obvious congenital malformations [patient] does the presence of a single umbilical artery [risk factor] necessitate further investigation [intervention] to exclude associated malformations [outcome]?
Search strategy and outcome
Primary source: Medline via Pubmed using keyword “umbilical artery”. A total of 477 individual articles were found. This was limited to 152 articles by selecting those in English language and human studies relating to neonates (birth–1 month). The search was verified by using (MeSH) subject heading: “umbilical artery” + subheading: abnormalities. Individual abstracts were read. A systematic review with meta-analysis of the relevant studies which matched our structured clinical question was found. The meta-analysis and original articles of seven relevant included studies were appraised.
Secondary sources: Cochrane database and Best Bets. No further papers were identified.
See table 1.
Single umbilical artery has long been recognised as a soft marker for chromosomal abnormalities and congenital malformations. Autopsy series from aborted and still born fetuses report a high incidence of associated malformations. It is therefore conceivable that if SUA is detected in a neonate with obvious physical abnormalities, full investigatory work up to detect occult malformations of various organ systems has to be undertaken. Nevertheless, in many cases SUA can be an isolated feature. It is unclear if apparently asymptomatic infants with SUA need to be investigated.
The meta-analysis cited1 was a review of 37 studies published over the past 40 years. Eleven of the 37 studies were performed on specimens obtained from autopsy studies of abortusus and stillborn babies. These were not relevant to our question. In the remaining 26 studies, the diagnosis of SUA was made by clinical examination of the placenta or umbilical cord after delivery and thus satisfied our initial criteria. But in only seven of these was there data for asymptomatic isolated SUA. Overall, a mean of 16.2% of infants with isolated SUA had a renal anomaly (median 5.3%). In half these cases (8%) these malformations were severe and persistent on follow up. The most frequent major renal anomaly was vesico-ureteric reflux, grade 2 or greater, in 2.9% of the total population.
In the study by Bourke and colleagues,2 infants with isolated SUA had a screening ultrasound scan. Those with abnormal scans underwent a micturating cysturethrogram and urine cultures. Vesico-ureteric reflux (VUR) was documented in 4.5% of these infants. It is interesting to note that three of the five infants with VUR developed urinary tract infections (UTI) within the first five months of life.
The incidence of occult renal anomalies in the general paediatric population is about 2.5%;9 the prevalence of VUR in healthy individuals is unclear. Ransley,10 in a compilation of several publications, reports a rate of 1.3%.From the currently available evidence it seems that the incidence of silent renal abnormalities in infants with isolated SUA is at least threefold higher for severe malformations and sixfold higher for any renal malformation compared to the general paediatric population. VUR is probably up to three times commoner in these infants. A screening renal ultrasound scan may be useful in detecting occult structural malformations of the urinary tract. However, its positive predictive value in suggesting VUR was low; it was reported as 32.5% in a recent study.11 As VUR and UTI are believed to be forerunners of reflux nephropathy, it seems prudent to investigate infants born with an isolated SUA by means of a micturating cystourethrogram (MCUG) and maintain a low threshold to diagnose and treat urinary tract infections.
CLINICAL BOTTOM LINE
There is an increased proportion of significant occult renal malformations in asymptomatic infants born with an isolated single umbilical artery (8% total population).
A significant proportion of such infants may have vesico-ureteric reflux (grade 2 or worse).
Screening renal ultrasonography and micturating cystourethrography are useful investigations to detect associated renal anomalies in these cases.
There is a lack of data regarding malformations of other organ systems in infants with asymptomatic isolated SUA.
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