The process starts during pregnancy
If you're pregnant, you have no doubt noticed the huge metamorphosis occurring in your bra cups. Those physical changes - tender, swollen breasts, and darkened nipples and areolas (the circle of skin surrounding your nipple) - may be one of your earliest clues that you've conceived. Experts believe the colour change may also be a helpful aid to breastfeeding. It's nature's way of providing a visual guide that helps newborns feed successfully (hey, dinner's over here!). Another pregnancy signal: the appearance of tiny bumps around your areola called the glands of Montgomery (named after the British obstetrician who first described them), which also play a role in breastfeeding. These bumps produce an oily substance that cleanses, lubricates, and protects the nipple from infection during breastfeeding.
What's going on inside your breasts
Perhaps even more remarkable than this visible transformation is the extensive changes taking place inside your breasts. Your developing placenta stimulates the release of oestrogen and progesterone, which in turn stimulate the complex biological system that makes lactation possible.
oestrogen caused them to grow and swell. During pregnancy, those glands shift into high gear.
By the time your baby is born, the glandular tissue in your breasts doubles in size, which accounts for your bigger-than-ever breasts. Each one may get as much as 1½ pounds heavier!
Nestled amid the fat cells and glandular tissue is an intricate network of channels or canals called milk ducts. Pregnancy hormones cause the milk ducts to increase in number and size; the ducts then branch off into smaller canals near the chest wall called ductules. At the end of each one is a cluster of small, grapelike sacs called alveoli. A cluster of alveoli is called a lobule; a cluster of lobules is called a lobe. Each breast contains between 15 and 20 lobes.
Milk is produced inside the alveoli, which are surrounded by tiny muscles that squeeze the glands and push milk out into the ductules. Those ductules converge and lead to a bigger ducts that end in your nipple. (You can think of the nine or so milk ducts in each breast as individual straws that all end at the tip of your nipple and deliver milk into your baby's mouth.) Your milk-duct system becomes fully developed sometime during your second trimester, so you can breastfeed your baby even if she arrives prematurely. Before pregnancy, a combination of supportive tissue, milk glands, and protective fat makes up a large portion of your breasts (the amount of fatty tissue varies among women, which is why breasts come in such a variety of sizes and shapes). In fact, your newly tender, swollen orbs have been preparing for your pregnancy since you were a 6-week-old embryo in your own mother's womb. By the time you were born, your main milk ducts -- a network of canals that transport milk through your breasts -- had already formed. Your mammary glands stayed quiet until puberty, when a flood of the female hormone
Production heats up after the baby is born
Milk production and prolactin
You'll begin full-scale milk production within 24 to 48 hours of giving birth to your baby. Scientifically speaking, this period is called lactogenesis. Once you expel your hormone-producing placenta, the oestrogen and progesterone levels in your body start to drop. The hormone prolactin, which has been rising throughout your pregnancy, is released to do its work. This pituitary gland hormone signals your body to make lots of milk to nourish your baby. Laboratory studies also show that prolactin may make you feel more "motherly", which is why some experts call it the mothering hormone.
As your body readies itself for lactation, it pumps extra blood into the alveoli, making your breasts firm and full. Swollen blood vessels, combined with an abundance of milk, may make your breasts temporarily painful and engorged, but breastfeeding frequently in the first few days will help relieve any discomfort.
First comes colostrum
During the early days of breastfeeding, your baby will enjoy a concentrated, creamy-looking, high-protein, low-fat substance called colostrum. You may have leaked a few drops of this thick, whitish substance during the final weeks of your pregnancy (some women have this happen during their second trimester). The precious, easily digestible liquid is full of disease-fighting antibodies called immunoglobulins that strengthen your baby's immune system. Your breastmilk changes throughout the feed to suit your baby's needs.
For your baby to enjoy your milk, it must be "let down" or released from the internal alveoli. Here's how it happens: As your baby sucks your nipple, she stimulates the pituitary gland to release oxytocin - as well as prolactin - into your bloodstream. When it reaches your breast, oxytocin causes the tiny muscles around the milk-filled alveoli to contract and squeeze. The nourishing liquid is emptied into the ducts, which transport it to the milk ducts just below the areola. When she feeds, your baby presses the milk from the ducts into her mouth.
During the first days of feeding, you may feel some contractions in your abdomen as the baby sucks. The usually mild discomfort signals the release of oxytocin, which helps shrink your uterus back to its pre-pregnancy size. (This same hormone caused your uterus to contract during labour.) Another signal: You may feel calm, satisfied, and joyful as you breastfeed. No wonder some people call oxytocin the hormone of love!
As your milk flow increases, you may also feel some tingling, stinging, burning, or prickling in your breasts. Some women say their milk drips or even sprays during letdown. And it helps if you can create a peaceful environment - if you're relaxed during feeds, your milk will flow more freely and easily. In fact, many women compare breastfeeding to learning how to ride a bike: It may be tricky at first, but once you - and your baby - get the hang of it, it becomes second nature.