TRANSPOSITION OF THE GREAT ARTERIES
What is transposition of the great arteries (TGA)?
TGA is a congenital heart defect in which the large blood vessels which carry blood from the
heart to the lungs (pulmonary arteries) and body (aorta) are coming off the wrong pumping
chambers (ventricles). In the normal situation, the pulmonary artery comes from the right ven-
tricle and carries blue blood (less oxygen) to the lungs, and the aorta comes from the left ven-
tricle and carries red blood (more oxygen) to the body. In TGA the aorta comes from the right
ventricle and the pulmonary arteries come from the left ventricle.
What causes TGA?
There is no known cause of TGA. Some patients with TGA have genetic disorders. TGA does
not run in families, but there is an increased chance of having a congenital heart defect if a
relative also was born with a heart defect.
How is TGA diagnosed? What are signs and symptoms?
TGA is sometimes diagnosed by fetal ultrasound before the baby is born. First trimester
screening for chromosomal abnormalities is a good screening tool to identify patients who
might be at an increased risk for cardiac defects. If TGA is not detected before birth, babies
may initially appear healthy, although their oxygen levels will be decreased. They may appear
bluish in color, or have difficulty breathing or fast breathing. If TGA or another heart defect is
suspected, the baby will be evaluated by a pediatric cardiologist. That evaluation would in-
clude measuring the oxygen level, an electrocardiogram (ECG) and an echocardiogram
(ultrasound of the heart). The echocardiogram would show the abnormal structure of the
heart.
How will your pregnancy be managed?
If your baby is diagnosed with a TGA, a high-risk obstetrician will participate in your obstetric
care. Overall care should be transferred to a specialized center where multidisciplinary care is
available. The team should include a perinatologist, fetal and pediatric cardiologists, a genetic
counselor, a neonatologist and a pediatric cardiac surgeon. Fetal well being will be followed
closely by fetal ultrasound and nonstress tests. Towards the end of pregnancy, visits may be
as often as two to three times a week. If there is no specific maternal or fetal reason for a C-
section, vaginal delivery is often possible. Induction of labor is often scheduled for pregnancies
affected with TGA to make sure that all of the team members are available at the time of deliv-
ery.
Why does TGA make babies sick?
Since the arteries are hooked up wrong, the blue and red blood go to the wrong places. The
blue blood returns from the body to the right side of the heart. The blue blood is then pumped
from the right ventricle back to the body, without ever getting more oxygen. Meanwhile the red
blood returns from the lungs to the left side of the heart. It gets pumped from the left ventricle
back out to the lungs. The two circuits are separate, and the body is not able to get the oxy-
gen it needs. These makes babies turn blue, due to low oxygen levels, and could eventually
lead to babies becoming very sick.
Center for Advanced Fetal Care, University of Maryland Medical Center, 22 S Greene St, Baltimore, MD 21201, 410-328-6640
Children’s Heart Program, University of Maryland, 110 S Paca St, 7th Floor, Baltimore, MD 21201, 410-328-4348
