After the egg and sperm have united and run to the uterine cavity to develop and grow, it is normal to detect pregnancy only after 20 days, not late implantation. Usually, if you get pregnant after ovulation, the earliest you can see the gestational sac on ultrasound is 37 days after menopause, and after 40 days it is called late implantation. It is 20 days after ovulation when the embryo is in bed. Generally, you can check if you are pregnant only after 5 weeks of pregnancy with the early pregnancy test, but the blood test is relatively earlier. The principle of pregnancy detection is the value of hCG. Initially, there is less of this hormone in the human body and it is not easy to detect it, so it can be detected only after 20 days. It is recommended to go to the hospital regularly after pregnancy, take pregnancy tests according to the doctor’s requirements, screen for related diseases, pay attention to supplementing meat, eggs and milk and other nutrients, pay attention to rest and avoid heavy physical activities and strenuous exercise. If you have any uncomfortable symptoms, go to the hospital in time.