Before birth

It's possible for a baby to be diagnosed with hypoplastic left heart syndrome while it's still in the womb. Your doctor may be able to identify the condition on a routine ultrasound exam during the second trimester of pregnancy.

After birth

After your baby is born, his or her doctor may suspect a heart defect, such as hypoplastic left heart syndrome, if your baby has grayish-blue skin or has trouble breathing. Your baby's doctor may also suspect a heart defect if he or she hears a heart murmur — an abnormal whooshing sound caused by turbulent blood flow.

Doctors usually use an echocardiogram to diagnose hypoplastic left heart syndrome. This test uses high-pitched sound waves that bounce off your baby's heart to produce moving images that can be viewed on a video screen. In a baby with hypoplastic left heart syndrome, the echocardiogram reveals a smaller than normal left ventricle and aorta, and it may also show abnormal mitral or aortic valves.

Because this test can track blood flow, it also shows blood moving from the right ventricle into the aorta. In addition, an echocardiogram can identify associated heart defects, such as an atrial septal defect.