After you are treated for gestational trophoblastic tumor, your doctor will want to make sure that the tumor is fully gone before you become pregnant. This is because the main way to determine if the tumor is gone is to follow your blood levels of human chorionic gonadotrophin (HCG). Beta-HCG levels are usually elevated with GTT, but should return to normal with effective removal. Because HCG levels also rise if you are pregnant, becoming pregnant will interfere with the usefulness of HCG as an indicator of remaining disease. This may prevent you from getting appropriate treatment. Pregnancy should therefore be avoided until your doctor approves, which is usually six months to two years after the last treatment.