The reason for menstruation during breastfeeding is that the ovaries resume normal hormone metabolism with ovulation and the endometrium is affected by hormone levels, resulting in menstruation. The level of prolactin in breastfeeding women is usually high. Under the regulation of high prolactin level, it enables the breasts to produce milk normally, but it also inhibits the secretion of folliculogenic hormone and luteinizing hormone, thus inhibiting ovarian function, and ovulation does not occur, and there is no menstruation. Over time, the secretion of lactogen will gradually decrease, the ovaries will resume ovulation and start to secrete estrogen and progesterone periodically, and the endometrium will start to shed periodically, leading to the onset of menstruation. Menstruation during breastfeeding is a normal physiological phenomenon, but the situation of menstruation varies from woman to woman, some may have normal menstruation every month, while others may resume menstruation 1-2 months after they stop breastfeeding, which is related to the state of hormone levels. In addition, it is important to use contraception during breastfeeding to avoid pregnancy while breastfeeding, regardless of whether or not you have a period.