Each nipple contains nerve endings, muscle fibers, sebaceous glands, sweat glands and about 20 milk ducts. The nipple is surrounded by the areola, a circular, pigmented area. Before pregnancy, the areola is usually pink. It turns brown or red-brown and enlarges during pregnancy and lactation. A darkened areola may act as a visual signal for the breastfeeding infant.
Breasts undergo many changes during pregnancy.
In the early weeks, a common symptom of pregnancy is tingling or soreness of the breasts. After about 8 weeks of pregnancy, your breasts may grow larger and become nodular or lumpy as glands and ducts inside the breasts grow and develop. As your breasts change during pregnancy, you may notice veins appear just beneath the skin. During the second trimester, a thin yellow fluid called colostrum begins to form. It can sometimes be expressed from the nipple by gentle massage.