This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fetal Disorders, Subject name: Gynaecology & Obstetrics
Which of the following closes before birth: 
Select and explain. 
A. Ductus arteriosus, B. Ductus venosus, C. Cardinal vein, D. Umbilical vein
C: Cardinal vein
Answer: C: Cardinal vein 
Explanation: Ans. (c) Cardinal veinRef: D.C. Dutta 8th ed. / 50* The cardinal veins form as the basis for the intraembryonic venous part of the circulatory system. Various venous systems appear in various stages of the embryogenesis and partially disappear again. Very early in the development two paired systems appear:# The superior cardinal veins bring the blood from the head region via the left and right common cardinal vein# The inferior cardinal veins drain the blood from the lower half of the body into the two common cardinal veinsFrom here, the blood is emptied into the sinus venosus and into the atrium via the sinus horns.Rest of structures given in option closes AFTER birth, with following sequence:U- Umbilical veinF- Foramen ovaleA- Ductus ArteriosusV- Ductus Venosus