Signs milk is coming in during pregnancy

Clinically reviewed by Sandra Jennings-Curry, RN, MSN, IBCLC, CNL

One of the most common pregnancy symptoms is changes in your breasts. Anything from tingling, leaking, or a feeling of fullness. You might be wondering: is this milk coming in already? The answer is yes, it might be. Your body starts preparing to feed your baby well before birth, and for many people, that means milk production begins during pregnancy.

When does breast milk come in during pregnancy?

Your body typically begins producing breast milk before your baby is born. This starts with colostrum, a thick, yellowish fluid that starts forming as early as 16 weeks into pregnancy. Some people notice a little leaking in the second or third trimester; others don’t see any signs until baby arrives and both are totally normal!

In early pregnancy, rising levels of hormones like estrogen, progesterone, and hCG trigger a wave of changes throughout your body. These shifts help support your growing baby but they can also cause some noticeable symptoms. You might experience morning sickness due to increased sensitivity in your digestive system, or notice more vaginal discharge as estrogen boosts blood flow and stimulates the production of cervical mucus. Meanwhile, as your skin stretches to accommodate breast and belly growth, you may begin to see stretch marks forming. All of these signs are common, and often early indicators that your body is adapting to pregnancy.

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The stages of breast milk production

There are three main stages of milk production and each stage matches the baby's rapidly growing body and evolving nutritional needs.

1. Colostrum (during pregnancy through early postpartum)

Colostrum is often called “liquid gold,” and for good reason: it’s small in volume but packed with powerful ingredients that protect and nourish your baby in the first days after birth.

• High in antibodies: Colostrum is high in the antibody IgA, which lines your baby’s gut and helps defend against viruses and bacteria.
• Rich in white blood cells: Colostrum contains living immune cells that help fight infection and kickstart your baby’s immune system.
• Concentrated nutrition: A few drops of colostrum go a long way, delivering high levels of protein, minerals, and fat-soluble vitamins.
• Supports gut development: Colostrum helps support the lining of your baby’s intestines, reducing the risk of infection and future allergies.
• Natural laxative: Colostrum helps your baby pass meconium, the first stools, which supports early digestion and reduces the risk of jaundice.
• Tailored for newborn needs: Colostrum is low in fat and easy to digest, making it ideal for your baby's tiny stomach (which is about the size of a marble on day one).

Some pregnant people collect and store the colostrum that starts leaking during pregnancy, to start building up a supply that can be used to feed your baby before your milk comes in.  Consult with your health care provider or lactation consultant to make sure this is the right plan for you.

2. Transitional milk (about 3 to 5 days after giving birth)

Transitional milk, which your body produces around 3 to 5 days after giving birth, plays a key role in meeting your baby’s rapidly changing nutritional needs during the first week of life. It bridges the gap between colostrum and mature milk, and here’s what makes it special:

• Higher volume than colostrum: Your baby’s stomach is growing quickly, and transitional milk provides more fluid to meet that need.
• Balanced nutrients: Transitional milk contains a blend of protein, fat, and lactose to support early growth and brain development.
• Immune support: While not as concentrated as colostrum, transitional milk still contains antibodies and white blood cells that help protect against infection.
• Energy for rapid growth: Transitional milk has more calories than colostrum, which supports your baby’s increasing energy demands and helps regulate weight gain.
• Hydration: As milk volume increases, so does water content, keeping your baby hydrated without the need for additional fluids.
• Evolving composition: The makeup of transitional milk continues to change day by day, adapting to your baby’s developmental stage and feeding patterns.

Transitional milk is your body’s natural way of scaling up both quantity and complexity. It’s one more example of how your milk is perfectly matched to your baby from birth.

3. Mature milk (by the second week postpartum)

Mature milk is the final stage of breast milk production. It continues to evolve with your baby’s needs and offers a complete source of nutrition well into the first year and beyond.

• Balanced macronutrients: Mature milk provides just the right amounts of fat, protein, and carbohydrates to support steady growth.
• Dynamic and adaptive: Mature milk changes composition within each feeding and over time to meet your baby’s changing needs. Your milk is composed of foremilk and hindmilk. Foremilk being higher in water and lactose at the start of a nursing session to hydrate and provide quick energy vs. hindmilk a fat-rich milk at the end of feeding, helps your baby feel full and supports healthy weight gain and brain development.
• Rich in brain-building fats: Essential fatty acids like DHA support early brain and nervous system development.
• Sustained immune protection: While lower in antibodies than colostrum, mature milk still contains protective factors, enzymes, and hormones that support long-term health. When your baby latches, the antibodies may also increase in your milk if your baby is sick.
• Hydration and temperature regulation: Breastmilk is over 80% water and helps keep your baby hydrated while also adjusting temperature slightly in response to your baby’s body.
• Supports the microbiome: Prebiotics in mature milk feed the good bacteria in your baby’s gut, supporting digestion and immune resilience.

Signs your milk is coming in during pregnancy

Every body is different, but here are a few common signs to look for that your breastmilk may be coming in:

• Leaking colostrum: You may notice yellowish drops on your bra or nipples, especially in the third trimester.
• Tingling or fullness: Some people feel a tingling sensation as the milk ducts begin to fill.
• Darker nipples and areolas: Hormonal changes can cause the skin around your nipples to darken.
• More visible veins: Increased blood flow to your breasts can make veins stand out more.
• Breast growth: Your breasts may become noticeably larger as milk ducts develop.
• Feeling more emotional or hormonal: As your body preps for lactation, mood shifts can happen.

If you’re hand-expressing colostrum, seeing just a few drops is normal.

Factors that affect when your breast milk comes in

Several factors can influence the timing and volume of your milk supply, including:

• Hormonal shifts: After birth, a drop in progesterone and a rise in prolactin signal your body to produce milk; if these hormone levels are off, it can delay or reduce milk production.
• Chronic condition:: PCOS or thyroid issues  can interfere with the hormones needed for milk production and make it harder for your supply to fully establish.
• Past breast surgery: Procedures like breast reductions, augmentations, or biopsies can sometimes damage nerves or ducts involved in milk production.
• Medications: Certain medications, including those for mental health, fertility, or blood pressure, may affect milk supply depending on how they interact with your hormonal system.
• Stress or separation from baby after birth: Physical or emotional stress and delayed skin-to-skin contact can interrupt the natural hormone flow needed to bring in milk.
• Preterm labor or complications: When babies are born early or there are delivery complications, your body might need more time and support to establish a full milk supply.

If you’re unsure whether your milk production is on track, a lactation consultant can help you figure out what’s normal for your body.

What to do if your milk is delayed

If your milk hasn’t come in within five days of giving birth, or you’re concerned about low milk supply, know that you’re not alone, and there are effective ways to increase milk supply.

• Nurse or pump often: Feeding or pumping at least 8-10 times in 24 hours sends your body the message that your baby is here and needs milk, helping stimulate production.
• Prioritize skin-to-skin contact: Holding your baby skin-to-skin boosts oxytocin levels, which supports both bonding and milk letdown.
• Hand express colostrum if possible: Gently expressing small amounts of colostrum can help stimulate your milk ducts and encourage your body to increase supply.
• Watch for breast engorgement: When milk begins to come in, your breasts may become very full, firm, and tender. While this is a sign your supply is building, it can also make it harder for baby to latch or milk to flow. Gentle hand expression or pumping for comfort can help relieve pressure and prevent clogged ducts.
• Get personalized support from a lactation expert: Everybody is different, and sometimes milk production just needs the right environment and guidance to kick in. International Board Certified Lactation Consultants (IBCLCs) are specialized lactation professionals who can assess what’s going on and help you create a feeding plan that works for your body, your baby, and your goals.

Whether you’re exclusively nursing, combo feeding, or still figuring it out, support can make all the difference. A lactation consultant works with you to find the right strategies, whether that’s building your milk supply, exploring combination feeding, or just making feeding feel a little less overwhelming.