Single umbilical artery (SUA), also known as a two-vessel cord, refers to the congenital absence of one of the two arteries in the umbilical cord. A normal umbilical cord has three vessels: one vein, which brings nutrient-rich blood from the placenta to the baby, and two arteries, which carry deoxygenated, nutrient-depleted blood from the baby to the placenta. Single umbilical artery is one of the most common fetal malformations. Single umbilical artery has an incidence rate ranging from .9% to .48% of all births in the United States. Single umbilical artery occurs equally in both genders, and it is three to four times more prevalent in twin pregnancies than in single pregnancies.
Single umbilical artery can occur as an isolated malformation, most reliably diagnosed by color Doppler ultrasound. A detailed scan of fetal anatomy is recommended to rule out additional fetal anomalies. If there are associated anomalies present, a fetal karyotype may be recommended to screen for aneuploidy and other chromosomal anomalies. Trisomy 13, trisomy 18, trisomy 21 (Down syndrome), and Turner syndrome are all associated with single umbilical artery, with trisomy 18 being the most common chromosomal abnormality.
Single umbilical artery is associated with an increased risk of perinatal mortality, intrauterine growth restriction (IUGR), and premature birth. Single umbilical artery is associated with both polyhydramnios and oligohydramnios as well as congenital diaphragmatic hernia, omphalocele, and malformations in a wide variety of organ systems, including heart, brain, skeleton, intestines, and genitourinary. The recurrence risk for single umbilical artery varies based on the presence of additional anomalies.