How Many Arteries Connect a Baby to His Mother?
The placenta is the only organ that is shared by two people: a mother and fetus. The placenta is quite vascular and many arteries and veins connect it to the uterus. The fetus is connected to the placenta by the umbilical cord, which exchanges blood between the fetus and the placenta.
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Anatomy
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The umbilical cord consists of three blood vessels. Two arteries carry venous (no oxygen) blood away from the fetus while a vein carries oxygenated blood to the fetus. This is the reverse of typical cardiovascular anatomy because arteries usually carry oxygenated blood and veins carry blood containing carbon dioxide and other wastes. The arteries and vein are held together by the amniotic membrane and covered with a mucus-like connective tissue called Wharton's jelly.
Fetal Connection
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The umbilical cord connects to the fetal abdomen. The umbilical vein connects to the left portal vein that carries blood to the liver. The umbilical arteries course downward alongside the bladder and connect to the internal iliac arteries. It is this anatomy that is imaged during ultrasound examination to verify that there are two arteries present in the umbilical cord. Using Doppler, the two arteries can be visualized on either side of the bladder.
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Variation
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In some pregnancies, there may be only two or four blood vessels. Two-vessel cords are more common. While this variation in the number of umbilical blood vessels may be associated with other fetal anomalies, pregnancies with this variant are often quite normal. The two-vessel cord varies anatomically in that it only has one artery. Ultrasonically, only one artery is seen alongside the bladder and connecting to an internal iliac artery. Four-vessel cords are rare.
Two-Vessel Cords
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There may be some risks associated with one umbilical artery. There is an increased risk of chromosomal abnormalities such as trisomies 13, 18 and 21. There is a chance that intrauterine growth restriction may occur. Intrauterine growth restriction is decreased weight with a smaller abdominal circumference in relation to the head circumference. There is also an increased risk for congenital anomalies affecting various systems of the body.
Length
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The umbilical cord and its blood vessels measure between 40 and 60 centimeters (15.7 to 23.6 inches). There are several theories regarding the length of the umbilical cord. One theory states that the umbilical cord length is determined by the amount of amniotic fluid present earlier in the pregnancy. Another theory states that shorter umbilical cords are associated with lower IQ scores, while very long cords are associated with hyperactivity.
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