During pregnancy, due to the change of hormone level in pregnant women’s body, breasts will appear swollen, painful and enlarged to prepare for lactation after delivery. After pregnancy, the placenta secretes a lot of estrogen to stimulate the development of mammary ducts and a lot of progesterone to stimulate the development of mammary alveoli, so the breasts start to increase in size in early pregnancy and become engorged with blood, and pregnant women feel that their breasts are swollen and painful, which is a common manifestation of early pregnancy. With the enlargement of the breast follicles and the appearance of nodules, the nipples become darker and more erect, the surrounding areola deepens in color, and the peripheral sebaceous glands become hypertrophied to form scattered nodular elevations, called Montessori nodules. During pregnancy, the mammary glands are fully developed in preparation for lactation after delivery, and no milk is produced during pregnancy because of the large amount of estrogen and progesterone that inhibit milk production. In late pregnancy, especially near the delivery period, due to the decline of estrogen and progesterone levels, a small amount of thin yellowish liquid will be overflowed from the squeezed breast, called colostrum; after delivery, due to the rapid decline of estrogen and progesterone levels, coupled with the newborn sucking on the nipple, milk officially begins to be secreted. All in all, it is normal for the breasts to change under the effect of hormones in the pregnant woman’s body after pregnancy. If breast pain occurs in the early stage of pregnancy, pregnant women can not be too nervous, after 3 months of pregnancy will be significantly relieved; if the pain does not ease or gradually worsen, you can consult a doctor to find out the cause.