You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is The most common cause of the congenital heart defect is: and explain in detail?
Congenital heart disease is not uncommon, occurring in about 8 of every 1000 live births.
One of the most common causes of congenital heart defects is a viral infection in the mother during the first trimester of pregnancy, when the fetal heart is being formed.
Defects are particularly prone to develop when the expectant mother contracts German measles; thus, obstetricians may advise termination of pregnancy, if German measles occurs in the first trimester.