This condition exists and after pregnancy, the breasts are changing as the body is changing due to progesterone and as the number of weeks of pregnancy increases.
Also during pregnancy, the mother prepares herself for breastfeeding, so the mammary glands become well developed and the breasts subsequently become larger. And there are pituitary prolactin receptors in the mammary cell membranes and oestrogen and progesterone receptors in the cytoplasm, which leads to the development of mammary ducts, proliferation and development of breast follicles and enlarged breasts.