The third to fourth day after fertilization is the blastocyst stage, and transplantation is needed at this time. After transplantation, the fertilized egg locates, adheres and invades, and finally the blastocyst is completely buried in the endometrium and covered by the endometrium, which is implantation. This time takes 3-4 days, that is, the seventh day after fertilization, the fertilized egg will be implanted and the chorionic gonadotropin in the blood will increase. This time is not very certain either. Sometimes it is normal to advance 1-2 days and postpone 1-2 days. After blastocyst transplantation, some people will have a small amount of bleeding because of implantation and rupture of endometrial blood vessels. If the amount of bleeding is small, it will be clean in 2-3 days, which is normal and does not need treatment.