Usually, vaginal bleeding does not occur before pregnancy. However, the possibility of individual pre-pregnancy bleeding cannot be ruled out and needs to be analyzed on a case-by-case basis. If you have vaginal bleeding before pregnancy, and the bleeding occurs within 30 days after your last menstrual period, the amount of bleeding is small, the duration of bleeding is short, and the results of the HCG test are significantly elevated, then you may consider that it is a case of bleeding on implantation. The bleeding at implantation is a rather specific manifestation, mainly caused by a transient change in the estrogen level in the body during the process of implantation. In addition, it may also be due to luteal insufficiency. Women with preconception bleeding are advised to have their blood tested for HCG and progesterone after pregnancy to see if both values are normal. In conclusion, women with vaginal bleeding should, on the one hand, dynamically monitor HCG levels and analyze the development of the embryo. On the other hand, if the progesterone is low in intrauterine pregnancy, progesterone supplementation should be taken in time to correct the progesterone deficiency.