Single Umbilical Artery

Single umbilical artery is a cord with only two vessels, one artery and one vein, instead of two arteries and one vein. It results from agenesis or atrophy of one artery. It matters because some fetuses have another anomaly (cardiac, renal, skeletal, chromosomal), and an isolated finding can still be linked with growth restriction and preterm birth.

• Risk factors: diabetes, epilepsy, twin pregnancy, advanced maternal age, smoking.
• Left artery is absent more often than the right.
• Isolated single artery has good outcomes in most.

Women have no symptoms. The finding is made at the mid pregnancy scan, or the baby's cord is found to have two vessels at birth.

• Normal examination.
• Fundal height may be small if growth is restricted.
• Differential diagnosis: normal variation at the placental insertion, atrophy of one artery after thrombosis, fusion of the two arteries near the placenta.
• Complications: fetal growth restriction, preterm birth, renal tract anomaly, cardiac anomaly, chromosomal abnormality, stillbirth, perinatal death.

The approach is ultrasound with colour Doppler on both sides of the fetal bladder, and a detailed search for other anomalies.

• Colour Doppler of the fetal pelvis: one artery lying beside the bladder instead of two; free loop cross section showing 2 vessels.
• Detailed anomaly scan at 20 to 22 weeks; fetal echocardiography; kidneys and spine.
• Karyotype by amniocentesis if any other anomaly or growth restriction is present.
• Maternal glucose test; growth scans every 4 weeks from 28 weeks and umbilical artery Doppler if growth is small.

The principle is to exclude other anomalies, to follow growth and to plan delivery at 39 to 40 weeks if isolated and normal.

• Supportive: reassure for an isolated finding; stop smoking; daily fetal movement counts; birth in a facility able to do caesarean section.
• Pharmacological: insulin or metformin 500 mg oral with meals increased to 1 g 12-hourly (maximum 2.5 g daily) for diabetes; betamethasone 12 mg IM twice, 24 hours apart, between 24 and 34 weeks and 6 days if preterm delivery is planned; aspirin 150 mg oral at night from 12 weeks to 36 weeks if uterine artery Doppler is abnormal; oxytocin 10 IU IM at birth.
• Procedures: growth scans every 4 weeks from 28 weeks for isolated single artery (every 2 weeks for growth restriction); induction at 39 to 40 weeks if isolated with normal growth; earlier delivery for growth restriction or abnormal Doppler; cord examination at birth to confirm the finding.
• Red flags: reduced fetal movements, falling growth centile, another anomaly on scan, abnormal Doppler.
• Follow-up: newborn examination; renal tract ultrasound at 4 to 6 weeks of age if other anomalies were found; genetic counselling if aneuploidy or a syndrome is found.