Breast swelling in the early stage of pregnancy is a normal physiological phenomenon. In the early stage of pregnancy, as hormone levels begin to increase, especially the levels of estrogen and progesterone, estrogen promotes the growth and development of mammary ducts, while progesterone promotes the growth and development of mammary follicles, and the whole breast will increase in size, and there will be the sensation of having a swollen breast. After the third trimester, hormone levels rise more smoothly, and the woman’s body has adapted to wearing loose, soft underwear, the phenomenon of breast swelling will gradually be relieved. If the breast swelling and pain is more obvious in the early pregnancy, or touch more obvious nodules, it is best to go to the hospital to do breast ultrasound to see if there is breast hyperplasia, or breast nodules and other breast diseases, and need to be given treatment as soon as possible.