It is not possible to detect pregnancy in the first week of pregnancy by a blood test because the secretion of human chorionic gonadotropin has not yet reached its peak and the amount is low. A blood test for pregnancy is performed by measuring the human chorionic gonadotropin level in the blood. In a normal woman in early pregnancy, the secretion of human chorionic gonadotropin begins around day 6 after fertilization of the egg, and human chorionic gonadotropin can be detected in the blood from day 7, and the serum level of human chorionic gonadotropin rises rapidly by day 8-10. The most correct and reliable way to diagnose early pregnancy is to perform an ultrasound examination, the earliest of which is about 1 week after the menstrual period. The ultrasound screen shows a circular halo in the uterus, also known as a pregnancy ring, and the dark area inside the ring is amniotic fluid. Vaginal ultrasound can diagnose early pregnancy one week earlier than abdominal ultrasound, and the appearance of a gestational sac in the uterus is the earliest image to appear in ultrasound diagnosis.