Women’s breasts will increase in size after childbirth because estrogen levels will increase significantly after pregnancy, and estrogen will promote the enlargement of the milk ducts and the coloring of the nipples and areolas, while progesterone will promote the development of the mammary gland follicles. In addition, pituitary prolactin, human placental lactogen and insulin will also promote the development of the mammary glands, all of which prepare for future lactation and breastfeeding. Therefore, a woman’s breasts will become bigger after having a baby to some extent. However, after breastfeeding, the breasts will still shrink and some will have sagging breasts, so it is recommended that you pay attention to sagging breasts after breastfeeding, wear comfortable and well-fitting underwear, and pay attention to the maintenance of your breasts.