This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Obstetrics, Subject name: Gynaecology & Obstetrics
Which of these changes in fetal circulation happen immediately at bih? 
Select and explain. 
A. Obliteration of ductus venosus, B. Formation of ligamentum teres, C. Functional closure of ductus aeriosus, D. Obliteration of distal hypogastric aeries
C: Functional closure of ductus aeriosus
Answer: C: Functional closure of ductus aeriosus 
Explanation: No anatomical closure or obliteration of either ductus venosus, or umbilical vein or foramen ovale occurs immediately at bih. It is only functional closure of these, that results from expansion of lungs at bih and lowering of resistance of pulmonary vasculature that results in change of blood flow pattern through hea from parallel to series like that in adults. Shunt/ vessel Functional closure Anatomical closure Remnant called as Ductus venosus 10-96 hrs after bih 2-3 weeks after bih Ligamentum venosum Ductus aeriosus At bih Several weeks after bih Ligamentum aeriosum Foramen ovale At bih 1 year after bih Fossa ovalis Umbilical vein Ligamentum teres Distal hypogastric aeries Umbilical ligaments