Infant breastfeeding. Illustration of a baby suckling at its mother's lactating breast. The female breast consists of 15-20 lobes of milk-secreting glands (here, coloured pink) embedded in fatty tissue. Ducts of these glands have their outlet at the nipple. During pregnancy, oestrogen and progesterone stimulate the milk-producing glands of the breast to develop, enlarge, and become active in preparation for breast-feeding. After birth, these glands first produce colostrum, rich in protein and antibodies, then milk. The baby's suckling reflex is present at birth. It instinctively sucks anything that touches the roof of its mouth.