As you experience all of the physiological changes preceding the birth of your baby, which ones are preparing your body to breastfeed? And how does the process work?
You probably noted early in your pregnancy—at around the fifth or sixth week—that your breasts had become fuller and your nipples were more tender than before. Your nipples and the darker-colored area around them, called the areolae, may have enlarged and darkened, and the small bumps on the areolae, called the Montgomery’s glands, became more prominent. Starting about the third month of pregnancy, the complex interplay of a number of hormones—including prolactin, estrogen, progesterone, and human growth hormone—leads to the proliferation of milk ducts and gland-producing cells in your breasts as your body prepares for milk production.
As your pregnancy progresses, the glandular tissue necessary to produce milk replaces much of the fatty and supportive tissue that normally makes up most of the volume of your breast. This causes your breasts to become substantially larger during pregnancy and lactation. Such changes may worry you that breastfeeding will cause your breasts to sag or change shape after weaning, but there is no reason for concern. Once your baby is weaned from the breast (when you stop nursing and your milk glands are once again replaced by fatty and supportive tissue) and you return to your prepregnancy weight, your breasts will return to their approximate prepregnancy size and shape.
By the end of the second trimester, your body has become fully capable of producing breastmilk—which means that even if your child is born prematurely, you will be able to produce breastmilk. Colostrum, the first milk produced, is thick, somewhat sticky, and yellow or orange in color. (If you notice yellow or orange stains on the inside of your maternity bra, your breasts are making colostrum. However, some mothers do not notice any colostrum being secreted until after their babies are born.)
After your baby is born, the areolae of your breasts, and especially the nipples, will become exquisitely sensitive to touch. When your baby’s mouth touches the nipple, nerve cells will send a signal to your brain, causing the release of the hormone oxytocin. Oxytocin causes tiny muscle cells within the breasts to contract, squeezing milk from the milk-producing cells down the milk ducts toward small sacs or sinuses near the nipples.
As your baby suckles at the breast, drawing milk from the sinuses through the nipple and into her mouth, the production of oxytocin will increase, causing more milk to be moved through the ducts in a process called the let-down or milk-ejection reflex. This is a simplified description of the complex system by which your body ensures that whenever your infant is hungry, your body will provide her with the nourishment she needs.