In the early stages of pregnancy, women feel breast swelling because the ovaries start to secrete progesterone and estrogen, which promote the growth of breast follicles and estrogen promotes the growth of breast ducts, and the whole breast will increase in size. After the third trimester, the ovaries will no longer secrete hormones, but the placenta will secrete hormones instead of the ovaries, and the level of hormones will remain at a high level after the third trimester and will not rise again. After pregnancy, women should pay attention to wearing loose, soft underwear, avoid squeezing the breasts, and keep the breasts locally clean and hygienic.