Overview

During the nine months of pregnancy, your body undergoes more changes than at any other time in your life. Your breasts, in particular, will experience significant transformations from the moment you conceive through the breastfeeding period. These changes include noticeable differences in appearance and sensitivity, as well as internal changes to prepare your body for lactation. Learn how your breasts will change, how much your breasts will increase in size, and how to manage symptoms such as sensitivity, leaking, and stretch marks. The more you are educated about how your breasts develop during pregnancy you can alleviate discomfort and develop a greater appreciation for the hard work your body is doing to prepare for your baby.

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The Anatomy of Breasts

Breasts are much more complex than they appear. Internally, the pectoralis muscles form the first layer of breasts. Next is a layer of fatty tissue that gives breasts their size and shape. Within the fatty tissue is a tree-like network of branched milk ducts. Externally is the areola, which is the darker skin surrounding the nipple. The areola contains small glands called Montgomery’s tubercles. In the center of the areola is the nipple, which has 4-18 ducts that connect to it.

Breast Development

A defining characteristic of mammals is that females produce milk to feed their young. The word mammal comes from the Latin word mamma, which means breast. Even your baby has mammary-specific cells as early as 4-6 weeks. Mammary glands are derived from a modification of sweat glands.

Hormones drive the development and all of the changes in female breasts. This starts in puberty with an increase in hormones, especially estrogen. Hormones are the same reason you may notice some changes in your breasts during a menstrual cycle. During pregnancy, you can expect a lot of changes as your breasts prepare for lactation. After menopause, your mammary glands atrophy and are replaced by connective tissue and fat.

Hormone Changes During Pregnancy

Hormones are the driving force behind all the physical and emotional changes you experience during pregnancy. Estrogen, prolactin, and progesterone are essential hormones contributing to breast changes.

Progesterone supports the formation and growth of milk-producing cells within the glands of the breasts. Estrogen stimulates the growth of the breast duct cells and generates the secretion of prolactin. Prolactin stimulates breast enlargement and milk production. This hormone is responsible for building lactocytes capable of secreting milk components. After you have your baby, your levels of estrogen and progesterone drop very quickly. The fall in these hormones and the rise in prolactin start milk production.

Breast Growth

Many changes alter how your breasts look and feel. One of the more obvious is that your breasts will get bigger. Most expecting moms will see their breasts increase in size, beginning in the first trimester of pregnancy. This happens as the ducts and alveoli in the breast multiply rapidly in preparation for breastfeeding. There isn’t much research on how breasts increase in size during pregnancy. One study showed that the average breast size increase didn’t change based on the initial size. Everyone is different, and you may not gain several cup sizes, but that seems most common across the whole population.

For some expecting mothers, larger breasts are a perk of pregnancy, but not everyone feels this way. Whatever feelings you have about your breasts before, during, and after pregnancy, I can assure you that you are not alone. For some women who already have large breasts, an increase in size is not a welcome change. For more information on challenges with large breasts, see this episode.

In one study, breast volume, milk production, and storage capacity decreased after six months. This makes sense because you introduce your baby to solid foods around six months. At 15 months, the 24-hour milk production was still substantial, even though breasts returned to pre-pregnancy size. Your breasts will go back to a smaller size, even if you continue extended breastfeeding, due to increased efficiency. Remember, your breasts work on a demand and supply system. The more milk you remove, the more you make. Plus, you calibrate your breasts separately. This means they may have different storage capacities and slightly different sizes. When your breasts go back to their pre-pregnancy size depends on how long you breastfeed and whether you return to your pre-pregnancy weight.

Sensitivity

Sensitivity, tenderness, and pain in the breasts are common early in pregnancy. This can start as early as one to two weeks after conception. For many women, this is one of the first signs of pregnancy. Soreness is caused by hormonal changes, retaining more fluids, and the breasts preparing for lactation.

If your breasts are sensitive or sore, wearing a supportive bra may be helpful even when sleeping. You may need to go up a bra size once or twice during your pregnancy. If you have the opportunity to go into a store and get fitted, that can be helpful. You will likely go up in the band and cup size.

Nipple sensitivity is another issue that can be very uncomfortable. You may find that having any clothing against your nipples is painful. If you are home and can go topless, you may want to try that. You also may want to let your partner know that your breasts are off-limits. Sensitivity and soreness should subside towards the second half of the first trimester.

Stretchmarks and Itching

Your breasts grow a lot during pregnancy, and that rapid growth can make your skin feel tight because it is stretching to accommodate your growing breasts. The tightening of your skin can make you feel itchy. The best defense for this is using a moisturizer to keep your skin hydrated and relieve the itch.

Another side effect is that you may get stretch marks. These are off-color lines that can appear on your breasts. They are lighter than your skin tone and can be pink or reddish. Stretch marks happen when the underlying supporting tissue stretches and tears during rapid stretching of your skin.

Using any moisturizer may help with itchy skin that often accompanies stretch marks. There is some research on topical treatments for stretch marks. The most promising ingredient I have seen from a research perspective is Centella Asiatica. If you want to use a product with this ingredient, I recommend the True Belly Serum from 8 Sheep Organics. You can save 10% with the code PREGNANCYPODCAST, and all of the 8 Sheep products come with a 100% Happiness Guarantee, and you can try it completely risk-free for three months. If you’re not 100% happy with your purchase, email them, and they will get you a refund within a day, no questions asked! The good news is that stretch marks do fade over time and will become less noticeable.

More Visible Veins

During pregnancy, your blood supply increases significantly by about 50%. One of the side effects of this change is that you may notice veins in your breasts become more noticeable. These are larger, blue veins you can see through the skin. Unless you sunbathe topless, your breasts are likely a lighter shade than more exposed skin. Visible veins are more prominent with lighter skin tones. The good news is that these visible veins will disappear with time and are not permanent changes.

Changes in Your Areolas

In addition to your breasts changing size and shape, you will also notice your areolas will get larger and darker. This is temporary, and after you have your baby, they fade in color. Over time, they may go entirely back to their pre-pregnancy appearance, or they may remain slightly larger and darker than they were pre-pregnancy. The color change is due to an increase in melanin. There is nothing you can do to prevent it. The sun can make it more pronounced. No judgment if you are sunbathing topless during your pregnancy, but that may make your areolas darker.

You may notice small bumps on your areolas. These are small glands called Montgomery glands or Montgomery tubercles. They get that name from an Irish obstetrician who described these in the 1800s. They are always there, but they get larger during pregnancy. The purpose of these glands is to secret oils that help to lubricate your areola and nipple. There is a lot of research demonstrating that these secretions also play an important role in breastfeeding. It turns out that these secretions have an odor that your baby can detect. A study that examined areolar secretions found that they play a crucial role in establishing behavioral and physiological processes of milk transfer and production. Newborns increased their behavioral and autonomic responses to the areolar secretion. Babies can detect these secretions and are attracted more to them than other stimuli.

Nipple Changes and Oxytocin

Changes don’t stop with your areolas. Your nipples will also change by getting bigger, sticking out more, and may even change shape slightly.  Like the changes to your areolas, your nipples will get smaller and go more back to what they were pre-pregnancy after pregnancy and cessation of breastfeeding.

Your nipples are an erogenous zone. This means that they are involved in arousal, and stimulation of your nipples prompts your pituitary gland to release oxytocin. There are several reasons why this is helpful during pregnancy, birth, breastfeeding, and postpartum.

Nipple stimulation may help bring on labor. One study that investigated this found it was associated with fewer inductions and more vaginal deliveries. A Cochrane review that included six trials found that significantly more women went into labor within 72 hours with the intervention of nipple stimulation. 37.3% of the intervention group was in labor vs. 6.4% of the group with no nipple stimulation. As a tool for naturally inducing labor, there is no downside to nipple stimulation as long as you aren’t stimulating your nipples to the point at which they are sore. The upside is that there is some evidence that this can start your labor.

Your newborn should latch to your breast within the first hour after birth. The sucking motion on your nipple causes your body to release oxytocin, which has two main effects. The first is that it reinforces that breastfeeding is a positive experience and increases bonding with your baby. The second is that oxytocin causes your uterus to contract, which can help your uterus shrink in size after you have your baby.

Breast Crawl

We often forget that every change going on in our bodies during pregnancy is designed for the survival of our babies. The changes in your breasts, areolas, and nipples are no exception. These changes are geared towards helping your baby find your breast and latch on to breastfeed. Babies can do this entirely on their own.

The breast crawl is a chain of events in which a newborn baby placed on its mother’s abdomen makes its way up its mother’s breast to initiate breastfeeding independently. This is pretty incredible to see and is such a testament to how instinctual breastfeeding is. 

For the first hour after birth, your baby should be very alert. Many instinctual behaviors will happen if your newborn is immediately placed on your abdomen. Your baby may put their hands in their mouth and taste the amniotic fluid, and they will also be able to smell it. They will get the same scent from your breasts because your areola’s glands smell like amniotic fluid.

Your baby will slowly crawl and wiggle up from your abdomen to your breast. This is not a quick process, and it does take some time. If you are speaking to your baby, they will recognize your voice, which will help guide them toward your voice and towards your breast. Your baby will reach for your nipple with their hand, which will make your nipple protrude out a bit more, making it easier for your baby to latch on. This stimulation also causes oxytocin release, which helps to shrink your uterus, prevent postpartum hemorrhage, and birth your placenta if that has not occurred yet. Your baby will start moving their mouth and salivating. As your baby gets closer, your areolas will help your baby spot your breast, even though their vision isn’t excellent at birth. Your baby will be able to lift their head and will bob their head until they can find your nipple, and they will latch on their own.

The experience from one baby to the next can vary greatly. Studies show that babies born via cesarean or in a medicated vaginal birth take longer or cannot complete the breast crawl more often than babies born vaginally without any medications. You can see that having larger and darker areolas emitting secretions with an odor and having larger, more protruding nipples all make it easier for your baby to find your nipple and latch on.

Colostrum, Milk Production, and Leaking

During your pregnancy, your body starts producing colostrum. This first milk has immunological properties. Most importantly, colostrum contains high concentrations of secretory immunoglobulin A. This is an anti-infective agent that coats your baby’s intestines to protect against the passage of germs and foreign proteins that could create allergic sensitivities. Another ingredient is a pancreatic secretory trypsin inhibitor, which protects and repairs the infant’s intestine. Colostrum helps seal your baby’s intestines. This is nature’s perfect food until your milk comes in. It may not seem like very much, but your baby’s stomach is the size of a marble at birth.

Leaking colostrum can happen during your pregnancy. This signifies that your body is working to prepare for breastfeeding. Not everyone leaks during pregnancy. Just because you do not see it does not mean your body is not producing it. Colostrum tends to be yellowish, and the consistency can range from thin to thick.

After your birth, it takes 3-4 days for your milk to come in. You will know this happens when your breasts feel huge and full. Once your milk comes in, leaking tends to be more common. This is especially true in the beginning when you are getting everything calibrated with your supply and your baby’s demand. If your breasts are full and you or your baby do not remove milk, they will leak. It is also possible to leak randomly, like when you hear a baby cry. If you are concerned about leaking, which happens, you will want to use some nursing pads. Pads are helpful during the day because it can be awkward to have your boobs leaking in public. They are also convenient to spare your sheets, bras, or clothing at home or at night. There are disposable and washable pads.

For more info on troubleshooting breastfeeding issues like cracked nipples, engorgement, and more, see this episode. Even though breastfeeding is instinctive, it isn’t easy for everyone. For more info on the basics of breastfeeding, click here.

I know you are dealing with a lot of changes during your pregnancy. It can be overwhelming. Understanding why these changes are taking place can help you have some compassion for the hard work your body is doing in preparing for your baby.

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