Colostrum is produced in very small amounts, which surprises many parents. After the effort of pregnancy and the expectation that the body will immediately produce substantial volumes of milk, a few millilitres of thick amber or clear fluid seems inadequate. It is not. Colostrum is one of the most concentrated biological fluids the body produces, packed with components that do specific work in a newborn that mature milk cannot replicate.
The small volumes are intentional: a newborn's stomach holds around 5-7ml at birth and the kidneys are not yet mature enough to handle large fluid volumes. Colostrum meets the need precisely while doing far more than just delivering calories.
Healthbooq (healthbooq.com) covers breastfeeding in the newborn period and beyond.
What Colostrum Contains
Compared to mature breast milk, colostrum has much higher concentrations of protein and much lower concentrations of fat and lactose. The protein content includes large amounts of secretory immunoglobulin A (sIgA), the dominant antibody of mucosal immunity. SIgA coats the lining of the newborn gut and respiratory tract, blocking pathogens from attaching to and crossing the gut wall.
Colostrum also contains lactoferrin (a protein that binds iron and has antimicrobial properties), lysozyme, and large numbers of white blood cells – macrophages, lymphocytes, and neutrophils – that provide additional immune protection. Some of these cells may cross intact into the newborn's circulation, though the mechanism and extent of this are still being studied.
Growth factors in colostrum, including epidermal growth factor (EGF) and insulin-like growth factor (IGF), support maturation of the newborn gut epithelium and close the leaky junctions between gut cells that are present at birth. This closure process – known as gut closure – reduces the ability of large proteins and pathogens to cross the gut wall, lowering the risk of sepsis and reducing exposure to allergens.
The yellow or orange colour of colostrum comes from beta-carotene, which has antioxidant properties.
Why Volume Is Small
Colostrum is produced in response to prolactin, which rises steadily during pregnancy. Progesterone, which remains high while the placenta is in place, suppresses large-scale milk production. When the placenta delivers, progesterone drops sharply, prolactin rises, and transitional milk begins to come in, typically 2-5 days postpartum. Before that, colostrum is all there is – and it is all that is needed.
The volume produced averages 7-10ml per feed in the first 24 hours and rises to around 15-30ml per feed by day 3. These volumes, combined with a newborn's stomach capacity and slow gut transit, are sufficient. Frequent feeding (8-12 times in 24 hours) matters more than volume at individual feeds.
Weight loss of up to 7% of birth weight in the first few days is normal and expected. Above 10%, assessment of feeding is warranted.
Antenatal Colostrum Harvesting
From around 36 weeks of pregnancy, women at higher risk of their baby needing supplemental feeding after birth can be offered the option of hand-expressing and collecting colostrum in small syringes, which are frozen and brought to hospital for use if needed.
The groups for whom antenatal harvesting is recommended by NICE and the Unicef Baby Friendly Initiative include: women with insulin-treated diabetes in pregnancy (babies are at higher risk of neonatal hypoglycaemia because maternal high blood glucose causes fetal hyperinsulinaemia), women expecting preterm or small-for-gestational-age babies, and women carrying babies with known conditions that may affect feeding, including cleft palate or Down syndrome.
Having a supply of expressed colostrum means that if the baby needs supplemental feeding, the mother's own milk can be used rather than formula, preserving all the immune and gut-protective benefits of colostrum and supporting the breastfeeding relationship.
Hand-expressing before 36-37 weeks is not recommended as nipple stimulation can trigger uterine contractions, though the evidence that this leads to preterm labour is limited.
Transition to Mature Milk
Transitional milk, produced from around days 3-5, gradually changes in composition over two weeks as volume increases. Fat and lactose rise; protein and immune component concentrations fall. By around 2 weeks postpartum, mature breast milk has established, though it continues to contain sIgA, lactoferrin, and other immune components throughout breastfeeding.
The timing of milk coming in is influenced by the frequency and effectiveness of feeding or expressing in the first days. Frequent removal of colostrum signals demand and accelerates the transition.
Key Takeaways
Colostrum is the thick, concentrated first milk produced from around 16 weeks of pregnancy through the first few days after birth. It is produced in small quantities – typically 7-10ml per feed in the first 24 hours – but is highly concentrated in immunoglobulins (particularly secretory IgA), growth factors, white blood cells, and nutrients. Its primary function is to provide passive immune protection and to coat and seal the newborn gut, reducing permeability and protecting against pathogens. Antenatal colostrum harvesting from around 36 weeks is now recommended for women at risk of low blood sugar in their newborn, including those with diabetes in pregnancy and those expecting preterm or small-for-gestational-age babies.
