Some parents, when changing the diapers of their 5- to 7-day-old baby girl, may find a bloody discharge from the baby’s vagina in small amounts, and the baby has no other uncomfortable reactions. Is it possible that a newborn baby has menstruation? In fact, this is a normal physiological phenomenon for newborn baby girls, called “pseudomenstruation”. Before the baby is born, she receives estrogen from her mother in the womb. After birth, the baby’s source of estrogen from the mother’s body is interrupted, and the concentration of estrogen in the body suddenly drops a lot, usually to a very low level within 3-5 days, and the role of estrogen in supporting the proliferation and engorgement of the baby’s reproductive mucosa is interrupted. As a result, the endometrium that was proliferating and engorged with blood is shed, and a small amount of blood and some bloody secretions are removed from the baby girl’s vagina, as if she is having a “period”. The bleeding is very small and usually disappears on its own after 2 to 4 days and does not require medical attention. The blood and discharge from the vagina can be gently wiped away with sterile gauze or cotton swabs, but not with local dressings or compresses, as this can cause infection. If the vaginal bleeding is heavy and lasts for a long time, the baby must be seen by a doctor promptly. In order to prevent vaginal diseases, you should use diapers that are absorbent and breathable for your baby, wash and change them regularly, and keep them hygienic. When the baby grows up, take off the crotch pants as soon as possible to avoid contamination of the exposed pubic area.