The placenta is an organ which develops within the uterus of a pregnant woman and provides blood, oxygen and nutrition to the fetus. The placenta is connected to the fetus by an umbilical cord. Inside the cord are two arteries and a vein; both arteries are referred to as umbilical arteries.
The two arteries wrap around the umbilical vein which carries oxygenated blood and nutrients from the placenta to the fetus. Once the oxygen and nutrients have been used, the umbilical artery transfers the deoxygenated blood and waste from the fetus back to the placenta. This waste and depleted blood then passes through the placenta and into the mother’s bloodstream, where it is carried to her kidneys for disposal.
These arteries extend from the cord into the pelvis. After birth, the arteries constrict when the umbilical cord is cut and tied. Within the body, these arteries become part of the medial umbilical ligament, a fibrous cord which runs from the navel to the pelvis, and the superior vesical artery, which supplies the bladder.
In a small number of cases, one umbilical artery, usually the left, is missing; a condition referred to as single umbilical artery (SUA). The cause of this abnormality is unknown, but occurs more frequently when the fetus is female, is twice as likely to be present if the mother is Caucasian rather than any other race, and is more likely to occur with multiple births than with single births. An increased frequency of miscarriage is associated with SUA, though this is probably a result of other abnormalities. While infants with SUA may have a lower birth weight, the fetus is able to receive sufficient nutrition to sustain itself during the pregnancy with only one artery.
Studies indicate that babies with SUA are at greater risk for certain birth defects. This abnormality can be detected during a prenatal ultrasound, though it is usually not discovered until birth. If there is any prenatal indication of a single umbilical artery, the physician may order a Doppler ultrasound, which is a preferred method to examine the fetal circulatory system.
The majority of infants with a single umbilical artery are born without any congenital or chromosomal defects. If defects are present, however, they can occur within a number of systems. Muscular skeletal problems such as a clubfoot or vertebral malformations may be present. Problems may also be found in the urinary, cardiovascular, gastrointestinal, and respiratory systems. While some of these abnormalities can be serious or fatal, others are minor, treatable or self-limiting. The lack of a second artery does not necessarily mean the infant will have serious complications, but the condition does warrant fetal monitoring and a thorough medical examination of the newborn.