Like some other congenital heart defects, the cause of TGA is unknown. However, there are a number of factors that have been associated with an increased risk of TGA, although they have not been shown to actually cause the defect. They include the following:

• Rubella (German measles) infection in the mother during pregnancy
• Other viral illnesses during pregnancy
• Poor prenatal nutrition
• Maternal alcoholism
• Maternal diabetes
• Maternal age over 40

Studies have found that maternal exposure during pregnancy to lawn and garden weed killers and rat poisons increases the risk of TGA to the developing fetus.