Making breastmilk: How your body produces Nature's perfect baby food

How will my breasts change during pregnancy?

Your breasts begin to prepare for feeding your baby as soon as you're pregnant. One of the earliest signs you’re pregnant are your tender, swollen breasts, caused by hormones surging through your body.

Some mums do not notice any change in their breasts but others may notice that the areolas, which are the areas of skin around your nipples, become darker and tiny bumps appear. This darkening of the areolas is nature's way of providing a visual guide to direct your baby towards her feed.

The tiny bumps around your areolas produce an oily substance that cleanses, lubricates, and protects your nipples from infections during breastfeeding.

By the time your baby is born, the glandular tissue in your breasts will double in size. When your milk comes in after your baby is born, your breasts will feel heavier and fuller. Each breast may be as much as 700g heavier!

How do my breasts make milk?

In each of your breasts are mammary glands, which are organs that produce breastmilk. Within each mammary gland are different parts which play a role in making breastmilk:

diagram of milk production in the breast

Alveoli. These are where breastmilk is made. Alveoli are clusters of small grape-like sacs in your breast. They are surrounded by tiny muscles that squeeze them to push milk out into the ductules.

Ductules. These are small canals that carry milk from the alveoli into the main milk ducts.

Milk ducts. These are the intricate network of canals which carry milk from the ductules and alveoli straight to your baby. Think of your milk ducts as individual straws that all end at the tip of your nipple and deliver milk into your baby's mouth. The ducts increase in size and number during pregnancy. You may have nine or so in each breast by the time you start breastfeeding.

You may or may not find that you leak a few drops of milk during your pregnancy. Your milk-making system will be ready some time during your second trimester. Your body is ready this early so that you'll be able to breastfeed your baby even if she arrives prematurely.

After your baby has been born and you have delivered the placenta, the oestrogen and progesterone levels in your body start to drop. This makes way for the hormone prolactin to be released from the pituitary gland in your brain. Prolactin signals your body to make lots of milk to nourish your baby. Prolactin can make you feel more maternal, which is why some experts call it the mothering hormone.

The stimulation that your nipple gets when your baby feeds is also an important part of how your body produces breastmilk. The stimulation sends signals to the body to release breastmilk at the start of a feed, also known as the let-down reflex. It also helps your body know that it needs to produce more milk. So feeding your baby often will trigger a healthy supply of breastmilk.

When can I start feeding my baby?

You can start feeding your baby as soon as she’s born. The first milk you'll feed your baby is a concentrated, creamy-looking, high-protein, low-fat substance called colostrum.

The precious, easily digestible liquid is full of disease-fighting antibodies called immunoglobulins that strengthen your baby's immune system. It is also specifically designed for your newborn's needs.

Your milk will come in about three days after you've given birth. This is when the levels of prolactin have adjusted and you can produce breastmilk rather than colostrum.

What happens when my baby starts to feed?

For your baby to enjoy your milk, it must be released from the alveoli, a process known as let-down. Here's how it happens:

breastfeeding flow chart
  • As your baby suckles, the sensation on your nipple causes another part of your pituitary gland to release oxytocin into your bloodstream.
  • When oxytocin reaches your breast, it causes the tiny muscles around the milk-filled alveoli to contract and squeeze, releasing milk.
  • Your milk moves along to the ducts just below the areola.
  • When your baby feeds, she presses the milk from the ducts into her mouth.

As your milk flow increases during let-down, you may also feel some tingling, stinging, burning or prickling in your breasts. You may find your milk drips or even sprays. If you have painful, engorged breasts during the first few days, feeding your baby often will help.

You may feel some contractions in your belly during the first few days as your baby suckles. These are called afterpains, and they feel like mild labour contractions. It's oxytocin getting to work again, shrinking your uterus back to its pre-pregnancy size.

Oxytocin is the same hormone that caused your uterus to contract during labour. You may also feel calm, satisfied, and joyful as you breastfeed. No wonder oxytocin is known as the hormone of love!

How do my breasts produce enough milk for my baby’s needs?

While your baby is feeding, her suckling releases more of the prolactin hormone. Prolactin, in turn, stimulates your body to make more milk. This places the order to your breasts to make enough milk for your baby's next feed.

As hours pass, the levels of prolactin start to fall again, but they get another boost when your baby feeds again. So the more often your baby breastfeeds, the more the prolactin levels in your bloodstream are boosted to produce milk. This is also the reason why your periods stop. Some mums use breastfeeding as a form of birth control. Consult your doctor if you are doing this as breastfeeding is not always the most efficient form of birth control.

Gradually, however, the prolactin response to your baby feeding reduces and your periods return. Your periods may come back even if you are still breastfeeding your baby exclusively.

You will still have plenty of milk, though. By this time, milk production no longer depends on prolactin, but on the stimulation of your baby feeding.

Your breastmilk contains a special protein called feedback inhibitor of lactation (FIL) that tells each breast how much milk to produce. If your baby empties a breast often, the levels of FIL in that breast will be low. Low FIL levels push up milk production.

If milk is not removed very often, perhaps because your baby has started solids, then FIL builds up and milk production slows.

FIL acts locally, and in each breast separately. This means you can reduce milk production in one breast, and continue to feed your baby with the other. FIL is also the reason why it is possible for one breast to produce enough milk to fully feed one baby. It also explains why a mum with twins can feed a baby on each breast.

If you feel you aren’t making enough milk to keep up with your baby’s demand speak to your doctor. Read our article on low milk supply for more help.

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