Breast milk is usually produced late in pregnancy until after delivery, especially from the end of pregnancy until after delivery. There is generally no milk secretion during pregnancy, probably because large amounts of estrogen and progesterone inhibit milk production. After the delivery of the placenta and the completion of labor, the level of estrogen and progesterone can drop rapidly, and when the newborn suckles on the nipple, there will be milk secretion. At the end of pregnancy, especially near the time of delivery, the breast is squeezed, a small amount of yellowish thin liquid can be overflowed from the nipple, often called colostrum. Although there is no milk secretion during pregnancy, the mammary glands are fully developed during this period to prepare for lactation, which is manifested by the development of enlarged breasts, deepening of the areola, and conscious breast swelling. Pregnant women usually pay attention to breast cleanliness and hygiene, do not wear tight tops, and do a good job of daily life care during pregnancy. Maintain a good mood, appropriate outdoor activities, regular maternity checkups. If you have any discomfort, you should go to the hospital in time to get a clear diagnosis from the doctor and cooperate with the doctor for symptomatic treatment.