A pregnancy test measures the level of HCG in the urine. The presence of two bars only indicates a high probability of pregnancy, but does not confirm the diagnosis. The principle of the pregnancy test is to detect HCG in the urine, when the level of HCG in the urine is high, it will show two bars on the pregnancy test. HCG refers to human chorionic gonadotropin, this hormone in the human body will be doubled after the fertilized egg implantation trend, which is an important indicator of pregnancy. Therefore, when the pregnancy test shows two bars, there is a higher probability that you are pregnant. However, pregnancy tests are biologically based and there may be quality and other issues that may cause errors in the results. Therefore, pregnancy cannot be confirmed simply by taking a pregnancy test. It is recommended that women with two lines on a pregnancy test should seek medical attention for a blood HCG test and ultrasound to determine if they are pregnant and if the pregnancy is normal.