When a woman is pregnant, her ovaries continue to produce estrogen and progesterone, so the high level of estrogen stimulation will cause the development of breast glands and ducts, resulting in breast swelling and discomfort. After one week of pregnancy, the phenomenon of breast swelling will begin, but if the fertilized egg is laid late, the time of breast swelling will be delayed to more than 10 days after intercourse, and it is not possible to judge whether a woman is pregnant simply by her breast swelling. Before menstruation, the estrogen and progesterone in women’s body will also reach a high level, which will also stimulate the phenomenon of breast swelling and pain.