Female students know that to be comfortable before the report of the great aunt you have to raise the cup of the corset first class, because the breast grows so little. In fact, this is the endocrine system is helping the breasts to prepare for a possible pregnancy. Ovulation occurs when estrogen production peaks in our bodies and progesterone production slowly increases. After the egg is released, there is a temporary drop in estrogen levels. However, 1-2 days after ovulation, the corpus luteum begins to secrete estrogen and produces large amounts of progesterone. Estrogen promotes the development of the milk ducts, while progesterone will further promote the development of the mammary glands on top of estrogen in preparation for nursing a new baby. With the development of the mammary glands and the “retention” of water and sodium in the body caused by estrogen (some edema before menstruation is also due to estrogen), the breasts will naturally be a little larger than usual, accompanied by a slight swelling and pain. But if the egg can not wait for the sperm to merge, 9-10 days after ovulation, the corpus luteum will begin to degenerate, atrophy, estrogen and progesterone levels will rapidly decline to the lowest level. Without the support of estrogen and progesterone, the mammary glands will stop developing and return to their original state. In this way, it seems that the breast swelling and abdominal pain before the arrival of the great aunt is the body in preparation for a possible pregnancy, as long as these symptoms can be relieved and disappear on their own after the great aunt is gone, the normal structure of the mammary glands are not disturbed, there is no nodule, it is all normal physiological hyperplasia.