High accuracy of over 99%. How it works: This Pregnancy test detects the HCG (Human Chorionic Gonadotropin) hormone that appears in the urine of a pregnant woman from the first days of conception. One Step Pregnancy Test Midstream gives accurate and clear results for the possibility of pregnancy. Similar to #1 brands such as Clearblue, 1st Response, Optimal and many others, this 99% effectiveness pregnancy test, instead of showing a clear blue mark, will show either 1 or two lines, 1 red line meaning "Not Pregnant" and 2 red lines meaning "Pregnant". This test is not an ovulation test and thus does not test for ovulation.