Breast milk

The hormonal balance of oestrogen and progesterone changes during pregnancy and causes the mammary glands (the milk-producing organ in a mother’s breast) to develop. From the 16th week of pregnancy, mothers are able to produce milk from their breasts but hormones inhibit milk production until birth. 

Content of breast milk

The consistency and composition of breast milk changes naturally according to the exact needs of each baby. There are differences according to the age of the baby, the time of day and the nutrition of the mother.

The content also varies depending on the following three different stages of milk production (lactogenesis stages).



Colostrum is the first fluid provided by mothers during the first days after birth. It is produced in low quantities with a relatively low concentration of fat resulting in lower nutritional quality. Therefore, it is ideal for the immature intestinal tract of newborn babies. It is highly digestible and supports the passing of meconium, the infant’s first stool. Additionally, colostrum is rich in components that help the babies to develop and to enhance their immune system such as lymphocytes, antibodies, growth factors and high protein levels.

Transitional milk combines some of the characteristics of colostrum with those of fully mature breast milk. It is usually produced from 5 to 14 days, or even longer after birth, and supports the nutritional needs of the rapidly growing baby during that time.

Fully mature milk is produced between 4 to 6 weeks after birth and remains almost unchanged during the rest of lactation.

The main macronutrients in breast milk are lactose, fat and proteins. They may vary depending on lactation stage and also within mothers. Fat is the most variable nutrient while lactose does not change much over different lactation stages or throughout the day. Also the so-called hind milk, which is the last milk of a feed, contains more fat than foremilk, which is defined as the initial milk of a feed.

Protein concentration is higher in the first weeks after birth and decreases after 4 to 6 weeks. Proteins like immunoglobulin A are very important for the immunity of the baby.

In addition, breast milk comprises various micronutrients such as Vitamin A, B1, B2, B6, B12, D, and iodine which also vary across women depending on their diet and body stores. They are relevant for the development and different organ functions of a newborn baby.

Benefits of breastfeeding

Several studies have confirmed the benefits of breast milk on health outcomes in newborns. Mother‘s milk protects babies against gastrointestinal and respiratory infections such as necrotising enterocolitis (NEC) (disease of the intestinal tract, caused by inflammation or decreased blood supply to the bowel), or pneumonia (lung inflammation). There is also a link between breastfeeding and a reduced risk of overweight and obesity in adults and a lower risk of type II diabetes and high blood pressure in later life. Additionally breastfed babies are at lower risk of sudden infant death syndrome (SIDS).

Some studies reported that breastfed children have a lower risk to develop clinical asthma, atopic dermatitis or eczema. For women breastfeeding can be beneficial by lowering the risk of bleeding after delivery as well as the risk of breast and ovarian cancer.

Breastfeeding or milk expression after a caesarean section is particularly important to help the uterus to begin to return to its normal size.

Children and mothers also benefit from skin-to-skin contact for example during breastfeeding or kangaroo care. Skin-to-skin care has shown to have positive effects on the baby and the mother and should therefore be initiated as soon as possible after birth and continued as long as possible afterwards. Kangaroo care may reduce postpartum depression the months following birth. Studies also show a physiological effect on preterm infants such as stabilised cardiac frequency, blood oxygen, and breathing frequency during the skin-to-skin contact.