The gray mark is an inconspicuous gray mark detected by the early pregnancy test paper when the human chorionic gonadotropin, or HCG, has just started to rise to the corresponding level after the formation of the fertilized egg. The appearance of the gray mark is a sign that the fertilized egg has been formed and has settled. As the fertilized egg settles, the HCG in the blood rises sharply and may become a clear red mark when tested again a few days later, which is the most common way to determine early pregnancy and test at home. This is the most common method to determine early pregnancy. After two obvious red marks are detected, you should go to the hospital for another examination to improve the blood HCG and progesterone test to confirm the diagnosis of early pregnancy, subject to the hospital laboratory test.