From Colostrum to Mature Milk: The Stages of Breastmilk Production Explained

Breastmilk production moves through three distinct stages in the weeks after birth. Each stage has a different composition — different proportions of protein, fat, carbohydrate, antibodies, and water — because each one is designed to meet a different phase of a newborn's development. The three stages are:

• Colostrum — produced from the final weeks of pregnancy through approximately the first three to four days after birth
• Transitional milk — produced from approximately days four to fourteen
• Mature milk — produced from approximately day fourteen onwards, continuing for as long as breastfeeding continues

The transition between stages is gradual rather than sudden, and the timing varies between mothers. Some mothers notice their milk "coming in" — the transition from colostrum to transitional milk — as early as day three; for others, this occurs closer to day five. Both are within a normal range.

Colostrum is the first milk — sometimes called liquid gold, not for its golden-yellow colour alone but for the extraordinary concentration of nutrients and immune factors it contains. It is produced in the mammary glands from around the middle of pregnancy, meaning it is present and available from the very first feed, even before the feeling of milk "coming in" occurs.

Volume

Colostrum is produced in small amounts — typically between 30 and 90 mL per day across all feeds combined in the first 24 hours. This volume feels alarmingly small to many new parents, particularly those who expect more visible evidence that their baby is being fed. But the newborn stomach is small — roughly the size of a marble on day one — and colostrum's density means that a small volume delivers a significant nutritional payload.

Composition

Compared with mature milk, colostrum is higher in protein, lower in fat, and much lower in lactose. This makes it easier for a newborn's immature digestive system to process. Its most distinctive feature is its immune content: colostrum is extraordinarily rich in secretory immunoglobulin A (sIgA), a specific antibody that coats the lining of the newborn's gut and respiratory tract, providing a layer of immune protection before the baby's own immune system is functional.

Key components of colostrum include:

• High concentrations of sIgA antibodies — protecting the gut and respiratory system from pathogens
• White blood cells (leukocytes) — providing direct immune defence
• Growth factors — supporting the maturation of the newborn's gut lining, helping seal the "leaky gut" that all newborns are born with
• High levels of Vitamin A, Vitamin E, and Vitamin K — nutrients that are critical in the first days of life
• A mild laxative effect — helping the baby pass meconium (the first dark stool), which reduces bilirubin levels and lowers the risk of newborn jaundice

What this means practically

The small volume of colostrum is not a sign of low supply. It is appropriate for a newborn's stomach capacity and nutritional needs. Frequent feeding in the first days — eight to twelve times in 24 hours — is normal and beneficial: it stimulates the prolactin receptors that establish the milk supply, and ensures the baby receives the full immune benefits of colostrum in the window when it matters most.

Transitional milk is the bridge between colostrum and mature milk. It emerges as the hormonal shift after birth — specifically the significant drop in progesterone — triggers a dramatic increase in milk production volume. This is the moment many mothers describe as their milk "coming in": a rapid increase in breast fullness that can feel overwhelming after the subtler presence of colostrum.

Volume

Volume increases substantially during this transition — from the 30–90 mL per day of early colostrum to 400–750 mL or more by the end of the first week, continuing to increase through week two as demand from feeding establishes the longer-term supply. This rapid volume increase is normal and does not mean the milk has changed quality — it has changed purpose.

Composition

Transitional milk contains lower concentrations of the immune proteins found in colostrum, but it retains meaningful levels of sIgA and other protective factors. As the immune concentration decreases, the caloric and macronutrient content increases: fat levels rise, lactose content increases, and the milk becomes more dilute and whiter in colour. This higher fat and calorie content supports the rapid weight gain that is the primary task of the first weeks of life.

Key changes during transitional milk:

• Increased fat content — supporting rapid brain development and caloric needs
• Higher lactose — the primary carbohydrate in breastmilk, supporting energy and gut microbiome development
• Increased water-soluble vitamins (B vitamins, Vitamin C) — meeting rising nutritional requirements
• Continued (though declining) immune protection from antibodies and white blood cells

What this means practically

The volume increase during transitional milk can produce engorgement — a period of breast fullness, heaviness, and sometimes firmness that occurs when volume outpaces the baby's current capacity to remove milk. Engorgement is normal and temporary, but it can make latch more difficult. Frequent feeding and responsive demand feeding during this period helps regulate supply to match the baby's actual intake. If concerns about supply arise during this stage — whether worry about too little or uncertainty about whether the baby is getting enough — our evidence-based article on how to accurately assess your milk supply provides a grounded framework for making that assessment.

By approximately day 14, breastmilk has reached its mature composition — though "mature" does not mean static. Mature milk continues to adapt throughout the breastfeeding relationship: its composition changes between the beginning and end of a single feed, between morning and evening, between illness and health, and between early infancy and toddlerhood. It remains a living, responsive substance.

Composition

Mature milk is approximately 87–88% water — which is why a well-hydrated mother is an important part of breastfeeding support, and why adequate fluid intake matters more than many mothers realise. The remaining 10–13% is a nutritional profile that provides everything a baby under six months requires: protein, fat, carbohydrate, vitamins, minerals, and a diverse array of bioactive factors including hormones, enzymes, and immune components that formula cannot replicate.

Key features of mature milk:

• Foremilk — the milk produced at the beginning of a feed, which is more watery and higher in lactose, primarily serving a hydration function
• Hindmilk — the milk produced as the feed progresses, which is higher in fat and calories, providing satiety and supporting weight gain
• Dynamic antibody response — mature milk continues to contain sIgA and other immune factors, and its antibody profile actually adapts in response to pathogens in the mother's and baby's environment
• Hormonal content that changes by time of day — including higher melatonin in milk expressed at night, which may support infant sleep-wake cycle development
• Adaptation over time — the composition of mature milk at six months differs meaningfully from its composition at 12 or 18 months, continuing to meet the changing needs of a growing child

Foremilk and hindmilk in practice

The foremilk-hindmilk distinction is real but often misunderstood. There is no clear moment when one becomes the other — fat content rises gradually throughout the feed as more fat is drawn from the alveoli into the milk. The practical implication is simply that a baby who feeds long enough to reach the higher-fat milk at the end of a feed will have a more calorically complete feed. Switching breasts very early in a feed, before fat content has risen, may reduce the caloric density of what the baby receives — though this is rarely a significant problem when feeding is responsive and frequent.

While the stages of breastmilk production are a natural process, there are circumstances where professional support is genuinely helpful:

• If your milk has not visibly increased in volume by day five to six after birth
• If your baby is losing more than 10% of birth weight and is not beginning to regain by day five
• If your baby has fewer than six wet nappies per day after day six
• If breastfeeding is significantly painful beyond the first week
• If you have a history of breast surgery, insufficient glandular tissue, or hormonal conditions that may affect supply

In these situations, an International Board Certified Lactation Consultant (IBCLC) can provide individualised assessment and support. The Australian Breastfeeding Association (ABA) helpline is also available 24 hours a day: 1800 686 268.

Understanding how breastmilk changes over time is the foundation for navigating many of the practical questions that arise through the breastfeeding journey:

• Return to the Breastfeeding Nutrition & Milk Supply Guide for the complete framework of evidence-based breastfeeding nutrition and supply support
• If you are concerned about your supply during any stage of milk production, read our evidence-based article on how to tell whether you have low milk supply or normal variation
• To understand what nutrition and galactagogue foods may support supply through the mature milk stage, our guide to 10 evidence-based ways to increase milk supply provides a practical, research-grounded overview
• Explore our range of breastfeeding hydration support products designed to support the high fluid demands of mature milk production

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