**2. Role in fetal life**

In a normal fetus, blood flows from right-to-left (PA to aorta) as a result of high resistance in the pulmonary arterioles and low systemic vascular resistance in the fetus and placenta. Patency of the ductus in fetal life is further influenced by oxygen content in the blood and prostaglandins. Dissolved oxygen content in the blood (pO2) leads to constriction of smooth-walled vessels, possibly due to the influx of calcium into the cell, thus ductal exposure to low pO2 in utero promotes patency of the ductus [2]. Prostaglandins are hormone-like compounds derived from arachidonic acid by cyclooxygenase enzymes (COX-1 and COX-2). Prostaglandin E (PGE) and prostacyclin (PGIE) are produced in the ductus and play a large role in maintaining its patency during fetal life [2–5].
