Normally blood donation does not cause delayed menstruation. Menstruation refers to the cyclical shedding and bleeding of the endometrium that accompanies the ovarian cycle and is influenced by the hypothalamic-pituitary-ovarian axis. For women with normal body functions, it will not affect the hypothalamic-pituitary-ovarian axis, nor will it affect the ovaries or the endometrium, so it will not lead to delayed menstruation. However, there are individual cases where blood donation may indirectly cause delayed menstruation. This is because, in addition to illness, mental and sleep factors affect the menstrual cycle. For example, if the donor is highly stressed and in a constant state of anxiety before and after blood donation, and sleeps poorly, it may affect a series of activities of the hypothalamic-pituitary-ovarian axis and lead to menstrual disorders, such as delayed or early menstruation. However, this situation is ultimately due to mental and sleep factors, and is not related to the loss of blood from blood donation, which has a good physiological regeneration mechanism and can be recovered within 1-2 weeks after donation. In conclusion, women who are eligible to donate blood will not experience delayed menstruation afterwards.