The difference between bleeding at the time of fertilization and bleeding during menstruation can be judged from the amount of bleeding, the duration of bleeding and the blood HCG level.
1. Bleeding volume: Bleeding at the time of implantation is caused by the stimulation of the uterine lining, and the bleeding volume is relatively small, while bleeding during menstruation is caused by the shedding of the uterine lining, and the bleeding volume is relatively large.
2. Bleeding duration: Bleeding during implantation is shorter and usually lasts about 1-2 days, while bleeding during menstruation is longer and usually lasts about 3-7 days.
3. Blood HCG: Blood test for HCG at the time of implantation will usually show a positive result, while blood test for HCG at the time of menstruation will usually show a negative result.
If a woman has abnormal bleeding after unprotected sex and is not sure if she is pregnant, it is recommended that she go to the hospital for an HCG test, which is the most accurate method.