Today’s Podcast

109:  Part 3 FAQ  How do the Breasts Make Milk?

Pregnancy is considered to be the period of the most extensive and rapid growth of the mammary gland.  Changes occur the fastest during the later states of pregnancy, which coincides with the most rapid period of fetal growth.

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How do the Breasts Make Milk?

Pregnancy is considered to be the period of the most extensive and rapid growth of the mammary gland. Changes occur the fastest during the later states of pregnancy, which coincides with the most rapid period of fetal growth.

Breast changes are one of the earliest signs of pregnancy. The areolas ( the dark areas of skin that surrounds the nipples) begin to swell followed by the rapid swelling of the breasts themselves. Many pregnant women experience tenderness down the sides of the breasts and tingling or soreness of the nipples. This is because the growth of the milk duct system and the formation of many more lobules.

Before I became pregnant the first time, I had no idea of the science behind this. I had no idea that hormones were responsible for these breast changes. With my first baby, I just knew that my nipples were incredibly sore. I never really paid them much attention up to this point, but all of a sudden my attention was drawn to my nipples a lot during the first trimester. Because they were so sore, I naturally looked at them more, which I had not spent much time doing before. They were getting darker and they were sticking out more. All to prepare for breastfeeding. How cool is that? Thank goodness the worst was in the first trimester and all but dissapeared in the third trimester.

The funny thing is though with each of my other pregnancies, I did not need any test to tell me I was pregnant. Each time there was this significant, what seemed like overnight change. probably gradually, but at some point in the first 6 weeks, all of a sudden I was distracted thinking of my nipples again. Sore nipples = pregnancy to me!

By the fifth or sixth month, the 20th – 24th week of pregnancy, the breasts are fully capable of producing milk. Many things are going on in your lovely mammary glands. Hormones are controlling the growth of the ducts and the glandular tissue. The prominence of the blood vessels in the breast and the enlargement and darkening of the areola are happening. All these changes are in preparation for breastfeeding your baby.

Your body does not discriminate. It just prepares to make milk. It does not know whether you are going to breastfeed or not, whether you are going to give birth prematurely or full term, whether you are birthing a baby who has special needs or birthing a baby you are going to have adopted or giving birth to twins. Your body is growing a baby and it is preparing to feed your baby.


With all of these changes and growth, your breast can increase up to almost a pound during pregnancy.

Blood flow to the breast can double during pregnancy

Increase in size during pregnancy, areola will darken during pregnancy. The skin surrounding your breasts will seem thinner, and the veins will be much more noticeable.

The Montgomery glands, which are those tiny little bumps on the areola that secrete natural oils to lubricate the area and help to prevent bacteria from breeding) will become larger and more noticeable

Nipples become more pronounced.

The ductal system expands and branches out under the influence of the hormone estrogen.

Progesterone helps to increase the size of the lobes and lobules – the branching network of the internal structure of the breast.

Each breast has many lobules, could be up to 20, that end in the nipple.

Many hormones are at work changing the inner workings of the breast tissue.

Also during this time, lymphocytes, plasma cells and eosinphils, which are all white blood cells.. well these are all gradually introduced into the small, narrow spaces between the tissue of the breast. To drill it down even further. – the lymphocytes are ( white blood cells that protect against disease and fight infection, the plasma cells are = white blood cells that secrete large volumes of antibodies and the eosinophils are ( white blood cells that fight against parasites and are gradually introduced into the small, narrow spaces between the tissue of the breast.

Can you freakin believe all the changes that are going on in the breast tissue,,, all in the first trimester?

Can you begin to see why I get so excited? Just wait til you learn what is happening in the second trimester

Second trimester changes:

Continued fascinating things all happening behind the scenes. There is more development and enlargement of the duct system and additional growth of the lobules

Some people think that you don’t start making food/milk for your baby until your baby is born or right before. Guess What? The breasts are busy making milk from the third month on.

The lovely hormone called prolactin triggers the production of colostrum which is your babies first food.

Your last trimester – More growth and development of ducts is going on. You now have secretory cells, which produce and secrete or release breastmilk.

How incredibly exciting is all this that is happening, all while you are just going on your merry way.
Each and every day, just doing your thing. and look at what busy ness is going on in your breasts.
I find this fascinating and hope you do too!

And the finale…. well it is really just the beginning, but I like to call it the finale, because the birth of your baby signals the end of all the crazy good stuff that goes on during pregnancy and you are now entering a new phase of lactation.

After the birth of your baby & the amazing placenta, further shifting of the hormones are happening. and the two most critical hormones in milk production which are prolactin and oxytocin are busy at work.

Do you want to be further wowed by this amazing fluid? Do you know that human milk is a living fluid. It is a secretion of the mammary gland and it is constantly changing its composition, dependent on the interaction with the baby.

And what it is made up of? Hundreds of ingredients that fall into the following categories:

the first thing to know is that breastmilk is about 90% water, which is exactly why you may have heard that breastfed babies do not need to be given any water as they are already getting plenty from you. Other great stuff: nutrient proteins, lipids, sugars, vitamins, minerals, hormones, enzymes growth factors and protective agents.

This is an ever changing fluid that is changed by – the stage of lactation, how old the baby is, timing of the feeding and your babies feeding patterns. One of my educators years ago said something that has really stuck with me.

She said – formula has, by and large the same 40-45 ingredients in the package. It can stay in that package for up to a year. And throughout the very first feeding after birth until the last feeding at the end of the first year, the ingredients all stay the same. For every single feeding.

While I have always known this to be true.. It is quite obvious. I had not yet, up until that moment, taken the time to contemplate the beauty and wonder of human milk. That it has several hundred ingredients and every feeding the baby has these nutrients, these ingredients are changing from one feeding to the next and even in the middle of feedings… more protein and water and sugars during some feedings and less during other feedings. Call me this crazy lactation consultant, but this just blew me away.

Now, this is the simple version of what is in breastmilk. Check out the link that is in the show notes that gives you a list of ALL the ingredients in breastmilk. Prepare to be ahmazed!

There is so much more to know about human milk. I don’t want to overwhelm you with information, but I find it hard to just stop right here. Just when you give birth and the whole milk making systems continues to go through some dramatic changes. Can I have just a few more minutes of your attention so I can tell you a few more amazing things? Great. Here we go:

During pregnancy and the first few days of postpartum, milk supply is hormonally driven. This is called the endocrine control system.
No matter what you do, your hormones are in charge of milk making.

The first phase in making milk is called Lactogenesis 1 and this happens halfway through pregnancy when you start making colostrum, the early milk. Ever wonder why you are not making large volumes of milk during pregnancy? Sure, you might experience some leaking, but the volume is still quite low. The high levels of progesterone needed during pregnancy inhibit milk secretion and keep the volume down.

The second phase in making milk is called Lactogenesis 2, which happens after birth with the abrupt hormonal shift once the baby is born and the placenta is out. Now the delivery of the placenta results in a sudden drop in a combination of the progesterone/estrogen and HPL levels. These changes in the presence of a high prolactin level now set the stage for copious milk production.

Within 2-4 days, moms have a sense of increased breast fullness. Now what is so amazing about this is again, your body is doing this all on its own.

Very quickly, you move into the next phase which is called… guess what? Lactogenesis 3. Now this is a very interesting phase because it is now as if a switch has been turned and that switch is from a mother driven milk supply to a baby driven milk supply.

This means that the supply will not increase all on its own. The breasts needs a lot of activity, meaning frequent and efficient milk removal, so it gets a strong message that you have a baby to feed. The more frequent the milk is removed, the more milk you will make.

Now the name of the game in the milk making department is to understand that you supply is very dependent on the frequency and efficiency of the milk removal. Babies tummies are very small, about the size of a small marble. Their tummy can only hold so much, which sends them back to the breast frequently. A baby who has an excellent latch and who comes to the breast for excellent feedings 7-9 times a day, will help you increase your supply to meet their needs.

You will often hear me say this. Information is powerful. Especially in new parenthood.
I hope that learning how the breasts make milk and how the breasts increase supply to meet your babies needs,
helps you out in the first few weeks of your babies life.

Newborns nurse very frequently and it can be quite exhausting. Having knowledge that frequent feedings are incredibly important to building a good supply, and that this is very normal, will help you get through the fatigue of the first few weeks.

If you are skipping feedings at night time to get more rest & not removing the milk, you may struggle with building a supply to meet your babies needs. There are ways to help you deal with this time period as you prepare for the birth of your baby. To help you with the preparation for the first few months postpartum, just check out the Show Notes for Episode # 9 and you can grab this handout.

A few last pieces of information to know. Despite all their best efforts, some mothers struggle with supply. There are some very real factors that can put you at risk for not making enough milk. This is what we will be talking about on next weeks FAQ #4

1. breast surgery – any kind.. implants, biopsies, breast reduction
2. retained placenta – this means that you have higher levels of certain hormones that will inhibit milk supply.
3. Sheehans syndrome/pituitary shock – frequent cause of this is pph
4. hormonal imbalance – thyroid is a common one
5. hormonal contraception – birth control pills and IUDs can make milk production hard for some moms.
6. insufficient glandular tissue.

You can also struggle to make enough milk if:

Baby is not at breast frequently enough = babies who are too sleepy to breastfeed OR if you are scheduling your babies feedings

Babies are not of efficiently enough – They do not have the best of latch. this can greatly affect milk transfer.

You can begin to understand my intense pushiness to get help from an IBCLC early on, if you feel you are at risk or are struggling with supply the first few days.

As always, I hope you find this information useful as you prepare to breastfeed your baby.
My greatest wish for you is that you will be breastfeeding your baby in comfort and with joy, have a good milk supply, a baby that is gaining well and that once you get past the first few weeks or so, you enjoy the convenience of breastfeeding your baby.

I will leave you today with this quote:

The benefits to the mother of immediate breastfeeding are innumerable, not the least of which after the weariness of labor and birth is the emotional gratification, the feeling of strength, the composure, and the sense of fulfillment that comes with the handling and suckling of the baby. ~Ashley Montague

Poster Link:

Poster Link:

Bonus Episode: Preparing for a C – section

Lori J. Isenstadt, IBCLC
Lori j Isenstadt, IBCLCLori Jill Isenstadt, IBCLC is a huge breastfeeding supporter.  She has spent much  of her adult life working in the maternal health field. Once she became turned on to birth and became a childbirth educator, there was no stopping her love of working with families during their childbearing years.  Lori became a Birth doula and a Postpartum doula and soon became a lactation consultant.  She has been helping moms and babies with breastfeeding for over 25 years.  Lori founded her private practice, All About Breastfeeding where she meets with moms one on one to help solve their breastfeeding challenges.  She is an international speaker, book author and the host of the  popular itunes podcast, All About Breastfeeding, the place where the girls hang out.  You can reach Lori by email at: [email protected] or contact her via her website:

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