The PDA is a blood vessel that is present in all babies when they are in the
womb, connecting the aorta to the pulmonary artery. In utero, the PDA diverts
blood away from the lungs, which are not involved in gas exchange before birth.
After birth, as the lungs expand and begin gas exchange, the PDA usually closes
spontaneously. In premature babies, however, this closure might not occur as
expected, leading to excessive blood flow to the lungs from the aorta.