A pregnancy test can typically detect a pregnancy as early as four weeks after conception, though this varies depending on the sensitivity of the test. Most home urine tests are accurate when used around two to three weeks after conception and may be able to detect hCG levels in your body as low as 25 mIU/ml. If you take a home pregnancy test at 4 weeks after conception and get a negative result, it is best to confirm that with another test in 1-2 weeks or through an appointment with your doctor.