Pregnancy can not always be detected by a blood draw. If ovulation is regular, a rise in blood HCG can be detected on day 7 of pregnancy. Under normal circumstances, it usually takes 7-10 days from the time the egg is expelled to the time it unites with sperm to form a fertilized egg, and then to the time the fertilized egg enters the uterine cavity and fuses with the endometrium and settles. The fertilized egg will secrete human chorionic gonadotropin (HCG), which enters the mother’s bloodstream, and the level of HCG in the blood can be checked to determine if the egg is pregnant. In addition, the HCG level can also be observed dynamically. In the early stage of pregnancy, it generally shows an increasing trend, which means that the embryo is in good condition, and after reaching the peak value in 8-10 weeks, it may show a plateau or a decreasing trend. If the menstrual cycle is irregular or there is delayed menstruation, it will interfere with the timing of the HCG test and it may not be detected accurately, so you can wait another 1-2 weeks for the test. In addition, you can also test your urine with early pregnancy test strips around 35 days after menopause or by urine HCG test to assist in determining if you are pregnant. It is important to note that a blood test at 7 days of pregnancy can only determine whether you are pregnant or not. If an ultrasound is performed at this time, the fetal sac is usually not yet visible. When the blood HCG is above 2000mIU/ml, ultrasound can be used to determine whether the pregnancy sac is in the uterine cavity to rule out the possibility of ectopic pregnancy and to observe the size and development of the pregnancy sac through ultrasound to prevent fetal abnormalities.