Blood HCG tests are often done clinically to determine if you are pregnant and the results are more accurate. Occasionally, however, there are cases where the blood test does not detect pregnancy, but it ends up being pregnant. After the fertilized egg is laid, the trophoblast cells secrete HCG, which can be detected in the blood on the first day after laying, i.e. about 8 days after ovulation. However, ovulation may fluctuate and the detection time may be delayed. If the blood HCG test is performed too early, the result of HCG elevation cannot be detected in the blood, so the blood test may not be able to detect it. Women of childbearing age with a history of menopause and sexual intercourse, who have delayed menstruation for more than 10 days, accompanied by symptoms such as loss of appetite, preference for sour food or aversion to greasy food, nausea, morning sickness, etc., can apply an early pregnancy test combined with a blood pregnancy test and ultrasound to determine whether it is an early pregnancy.