How breasts make milk in pregnancy and beyond

How will my breasts change in pregnancy?

Your breasts begin to gear up for feeding your baby as soon as you're pregnant. Having tingling nipples and tender, swollen breasts is one of the first signs of pregnancy (MIDIRS 2011). It's caused by hormones surging through your body.

The skin around your nipples (areolas) may also appear darker, and have tiny bumps. This is nature's visual way of directing your baby towards her feed.

The tiny bumps around your areolas produce an oily substance that cleanses, lubricates and protects your nipples from infection during breastfeeding (Geddes 2007). It smells like amniotic fluid, so your baby will instinctively move towards this familiar smell soon after birth (Doucet et al 2007, Doucet et al 2012).

By the time your baby is born, the glandular tissue in your breasts may have doubled in size. The timing of this change varies from woman to women. It can happen in mid- or late-pregnancy, or even after you've given birth (Geddes 2007, MIDIRS 2011).

Don't worry if your breasts don't seem to grow much in size. There's no link between the amount of breast growth and your ability to produce milk once your baby has arrived (MIDIRS 2011). When your milk comes in after your baby is born, your breasts will feel noticeably heavier and fuller.

How do my breasts make milk?

diagram of milk production in the breastMammary glands in your breasts produce breastmilk. Within each mammary gland, different parts play a role in making breastmilk:
  • Alveoli: where breastmilk is made. These clusters of small grape-like sacs in your breast are surrounded by tiny muscles that squeeze them to push milk out into the ductules. They develop during each pregnancy (Sternlicht et al 2006).
  • Ductules: small canals that carry milk from the alveoli to the main milk ducts.
  • Milk ducts: the intricate network of canals that carries milk from the alveoli and ductules straight to your baby. These ducts increase in size and number during each pregnancy. The average is nine or so in each breast by the time you start breastfeeding.
  • (Geddes 2007, MIDIRS 2011)

You may find you leak a few drops of milk during your pregnancy. In fact, your milk-making system will be ready to go some time during your second trimester (Geddes 2007). You'll be able to breastfeed your baby even if she arrives prematurely.

After your baby is 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 (MIDIRS 2011).

Prolactin signals your body to make lots of milk to nourish your baby, and may also make you feel more maternal.

When can I start feeding my baby?

You can start feeding your baby as soon as she's born. Having skin-to-skin contact immediately after the birth may help:
  • You and your baby to bond with each other.
  • Your baby's natural feeding reflexes to kick in.
  • To stimulate your milk to flow (Sullivan et al 2011).

The first milk you'll feed your baby is colostrum, which is a concentrated, creamy-looking, high-protein, low-fat substance. This is all your baby needs in her first three days of her life.

Colostrum is easily-digestible and full of disease-fighting antibodies (immunoglobulins) that strengthen your baby's immune system (Kent 2007).

Your milk will come in about three days after you've given birth (Kent 2007). This is when the levels of prolactin have adjusted and you produce breastmilk, rather than colostrum.

What happens when my baby starts to feed?

breastfeeding flow chartFor your baby to get your milk, it must be released from the alveoli, which is called letdown. Here's how it happens:
  • As your baby suckles, the sensation in 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, and release 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. (MIDIRS 2011)

As your milk flow increases during letdown, you may also feel some tingling, stinging, burning or prickling in your breasts (NCT 2012, Walker 2011). This is normal, and the sensation passes in a few moments.

You may find that your milk drips or even sprays as it comes down. If you have painful, engorged breasts during the first few days, feeding your baby often will help. This moves the milk through your breasts, which will help to avoid the milk staying in one of the ducts too long and causing infection (NHS Choices 2012).

You may feel some contractions in your belly during the first few days as your baby suckles (afterpains) (NCT 2012, Walker 2011). These feel like mild labour contractions. It's oxytocin getting to work again, shrinking your uterus (womb) 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 (Uvnäs-Moberg 2003), though this doesn't always happen (Bosco 2012).

How do my breasts produce enough milk for my baby?

While your baby is feeding, her suckling stimulates your brain to release more of the prolactin hormone. Prolactin 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. Prolactin is also the reason that your periods stop, as it can suppress ovulation. Some mums use breastfeeding as a form of birth control for the first six months, though this method isn't fail-safe (FPA 2012).

What happens to my milk over time?

Gradually, the prolactin response to your baby feeding reduces, and your periods return. Bear in mind that you may start ovulating again, even if you are still breastfeeding your baby exclusively (FPA 2012).

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 protein called feedback inhibitor of lactation (FIL). This 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. This acts as a signal for that breast to make more milk (Kent 2007).

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

Because FIL acts separately in each breast, you could reduce milk production in one breast, and continue to feed your baby with the other. FIL is also the reason why one breast can produce enough milk to fully feed one baby. So if you have twins, it's possible to feed a baby on each breast.

Last reviewed: December 2013


Bosco ML. 2012. Dysmorphic milk ejection reflex (D_MER). Fitzgerald Health Education Associates. [pdf file, accessed October 2013]

Doucet S, Soussignan R, Sagot P, et al. 2007. The "smellscape" of mother's breast: effects of odor masking and selective unmasking on neonatal arousal, oral, and visual responses. Dev Psychobiol 49(2):129-38

Doucet S, Soussignan R, Sagot P, et al. 2012. An overlooked aspect of the human breast areolar glands in relation with breastfeeding pattern, neonatal weight gain, and the dynamics of lactation. Early Hum Dev 88(2):119-28

FPA. 2012. Natural family planning. Family Planning Association. [pdf file, accessed October 2013]

Geddes DT. 2007. Inside the lactating breast: the latest anatomy research. J Mid Women’s Health 52(6):556-63

Kent JC. 2007. How breastfeeding works. J Midwifery & Women's Health 52(6): 564-70

MIDIRS. 2011. Female breast structure. Midwifery Information & Resource Service

NCT. 2012. Breastfeeding: a good start: feeding positions and attachment. [pdf file, accessed October 2013]

NHS Choices.2012. Mastitis. NHS Choices, Health A-Z. [Accessed December 2013]

Sternlicht MD, Kouros-Mehr H, Liu P, et al. 2006. Hormonal and local control of mammary branching morphogenesis. Differentiation 74(7):365-81

Sullivan R, Perry R, Sloan A, et al. 2011. Infant bonding and attachment to the caregiver: Insights from basic and clinical science. Clin Perinatol 38(4): 643–655

Uvnäs-Moberg K. 2003. The oxytocin factor. London: Pinter and Martin

Walker M. 2011. Influence of the maternal anatomy and physiology on lactation. Chapter 2 in Breastfeeding management for the clinician: using the evidence. 2nd ed. Sudbury, Massachussetts: Jones and Bartlett Publishers.

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Helpful information. I'm due to have my baby in February.
Thanks for the information. As a first time mum, I have learnt a lot from this site.
Thank u very much...very informative as its my first baby!!!
I am concerned that I had a breast lump removed a few years ago, is this going to cause me problems breastfeeding on one side!
Very informative..

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