FCPS part 1 Medicine solved mcqs with explanation Q12

Q12: A woman living at a hill station has had an uncomplicated pregnancy. She is brought to the hospital at the onset of labour. An ultrasound scan is performed which shows no fetal abnormality. The baby can still have which of the following conditions?

a) Transposition of great vessles

b) Patent ductus arteriosis

c) Limb defects

d) Tetrology of Fallot

Correct Answer: b

Explanation:

During fetal period, the ductus arteriosus shunts blood from the right to the left. It connects the pulmonary trunk with the aorta. Blood entering the pulmonary trunk from the right ventricle is shunted through ductus arteriosus into aorta. As the baby is born, the circulatory changes that occur also include closure of the ductus arteriosus. Closure of the ductus arteriosus is promoted by increase oxygen tension (when baby starts breathing) which decrease prostaglandin (PG) synthesis. At hill stations, the atmospheric oxygen pressure is low. A baby born and staying during the first few days of his life under such circumstances would lead to a decrease in oxygen tension and so failure of ductus arteriosus to close. Patency of ductus arteriosus can also be maintained by high PG levels such with use of indomethacin (a PG synthesis inhibitor). In summary low oxygen tension and high PG levels cause PDA.