It is possible to detect pregnancy with a test 8 days after fertilization, but the accuracy of the test may not be as high as when taken 1-2 weeks after the expected date of menstruation. It is recommended to follow the instructions on the test kit and consider retaking the test if you are unsure of the result. A positive result is usually accurate, but a blood test can confirm pregnancy even earlier. You can consult with your doctor or a healthcare provider for further advice and potentially request a blood test for more accurate results.