Final answer:
The normal umbilical cord contains three blood vessels: two umbilical arteries and one umbilical vein. In some pregnancies, there can be an umbilical cord with only two blood vessels. The answer to the student's question is option a) Two; three.
Step-by-step explanation:
The student has asked about the number of blood vessels normally found in the umbilical cord of a fetus. Normally, the umbilical cord contains three blood vessels: two umbilical arteries and one umbilical vein.
The two umbilical arteries carry oxygen-depleted blood from the fetus to the placenta, while the one umbilical vein carries oxygen-rich blood from the placenta to the fetus.
In about 1 percent of singleton and around 5 percent of multiple pregnancies, there can be an umbilical cord with only two blood vessels, instead of the normal three. This condition is known as a single umbilical artery (SUA).
The correct answer to the student's question is: About 1 percent of singleton and about 5 percent of multiple pregnancies have an umbilical cord that contains two blood vessels, instead of the normal three.