How do they suspect symptoms of asd in a newborn?

They don't. An atrial communication, a "hole", (pfo- patent foramen ovale) is present in all newborns. An ASD (atrial septal defect), a persistent important atrial communication is generally diagnosed later. The pfo closes soon after birth usually. A heart murmur or other abnormal heart sound is heard by the pediatrician at an office visit, and the child referred to a pediatric cardiologist for diagnosis.
No symptoms. ASD is asymptomatic for years if not decades. It is picked up by auscultation or echo. Therapy is done to prevent future rhythm problems or heart failure.