Breast pain can occur in the early stages of pregnancy. In the early stage of pregnancy, most pregnant women will find that their breasts are swollen and painful, and their nipples and areolas deepen in color and their breasts become larger. This is mainly because the level of estrogen and progesterone in the body increases after pregnancy, and estrogen stimulates the development of breast ducts and progesterone promotes the development of breast alveoli. The placenta also secretes large amounts of estrogen and progesterone and placental lactogen, which affect the development of the breasts. In early pregnancy, the breasts start to enlarge and become engorged with blood, and pregnant women can feel their breasts swelling, which is a common manifestation during pregnancy and is a normal early pregnancy reaction. This is a common early pregnancy reaction. As the breast follicles multiply and the breast gland enlarges, nodules will appear on the surface and the nipples will enlarge and deepen in color, making them easily erect. At the end of pregnancy, when you squeeze your breasts near the time of delivery, a small amount of thin yellowish fluid can spill out. During pregnancy, these changes in the breasts prepare for postpartum lactation.