There is no exact time frame for how many days it takes for the embryo to be expelled from the body without implantation, so no generalization can be made. Under normal circumstances, the sperm and the egg combine to form a fertilized egg that can be implanted in about 7-10 days, and some of the embryos that do not implant may be discharged with the vaginal secretions within 1 week, or may be discharged with the menstrual flow at the time of the next menstrual period, and the exact time varies from person to person. The failure of the embryo to attach causes a drop in estrogen and progesterone as well as HCG in the body, which can result in the shedding of the uterine lining like a menstrual period, which is known as a biochemical pregnancy. Therefore, it is recommended to go to the hospital for examination if you have abnormal menstruation during the preparation for pregnancy.