How much bigger the breasts will become during pregnancy is not fixed, there are individual differences. During pregnancy, the placenta will secrete a large amount of estrogen to promote the development of mammary gland ducts, but also secrete a large amount of progesterone to stimulate the development of mammary gland follicles, such as female pre-pregnancy mammary gland ducts and follicles are relatively more, such women’s breasts increase relatively more; such as female ducts and follicles are relatively less, the breasts increase relatively small, the specific size of the existence of individual differences. In addition to breast enlargement, pregnant women’s nipples will become black, areola deepening, sensitivity can increase, stimulation of the nipple can reflexively cause uterine contractions, at this time to reduce the stimulation of the breast; some pregnant women combined with mammary tumors can lead to abnormal enlargement of the breast, the need to seek medical treatment in a timely manner. Clinically, when pregnant women’s breasts are abnormal, they should consult a doctor as soon as possible to clarify the cause of the disease, so as not to delay the condition and lead to adverse consequences.