This is because during pregnancy the placenta secretes large amounts of estrogen, which stimulates the development of the mammary ducts, and progesterone, which stimulates the development of the mammary glandular follicles. The mammary glands are well developed and additionally require the involvement of pituitary prolactin, human placental lactogen and the insulin cortisol, and the breasts begin to enlarge and engorge significantly in early pregnancy. As the breast follicles proliferate, the breast enlarges and nodules appear. At this time, the nipples begin to enlarge, darken, and become easily erected, and the areolas deepen in color. The sebaceous glands at the periphery of the areola become hypertrophied and form scattered nodular elevations called Montserrat’s nodules. In addition, at the end of pregnancy, especially near the time of delivery, if you squeeze the breast, a small amount of yellowish, thin fluid may spill out, called colostrum.