After the sperm enters the female vagina, it meets with the egg in the fallopian tube and after the acrosome reaction and zona pellucida reaction, it fuses with the egg’s plasma membrane into the egg and forms a fertilized egg. 6-7 days later the embryo implants into the endometrium, which is called implantation. most pregnant women have no special reaction after implantation, a few pregnant women may have slight vaginal bleeding symptoms, the bleeding time is usually 3-5 days, usually not bright red blood, usually The bleeding usually lasts for 3-5 days and is not bright red, but is usually light pink or brown in color. The fertilized egg will stimulate the endometrium of the woman during implantation, causing endometrial movement and mild abdominal cramping or soreness, which is intermittent and usually occurs 6-7 days after ovulation. The amount of bleeding from implantation is small and manifests itself in various ways, such as in some cases only the presence of blood in the leucorrhoea or spotting, etc. The color is usually pink or brown, mostly in the form of a blood-colored discharge. Vaginal bleeding due to fertilization is one of the manifestations of functional uterine bleeding, which usually does not affect the growth and development of the fertilized egg and usually does not require special treatment. The abdominal soreness and bleeding caused by fertilized egg implantation are similar to the symptoms caused by menstruation and can be identified by blood HCG test. If a woman has recently had sex and has non-menstrual vaginal bleeding, she should promptly go to the hospital to check if the pregnancy is intrauterine. If the bleeding is only simple, it is usually not a problem and rest is sufficient.