A woman’s breasts start getting ready to make milk when she becomes pregnant. Breast changes are caused by four main hormones. These hormones cause the ducts and glandular tissue (alveoli) to grow and increase in size. Your breasts start to make the first milk, colostrum, in the second trimester. Colostrum is thick and clear to yellow in color. Once your baby and the placenta are delivered, your body starts to make more milk. Over the next few days, the amount of milk your breasts make will increase and the color will change to appear more watery and white.