In this defect, part of the aorta is absent and this leads to severe obstruction to blood flow to the lower part of the body. In the immediate newborn period blood flows through the ductus into the descending aorta and reaches the lower part of the body. As the ductus closes after birth, blood pressure in the lower circulation becomes inadequate and severe symptoms develop. Most affected infants develop severe symptoms (difficulty breathing and impaired kidney function) in the first week of life and need urgent surgery.