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).
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.
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.
There are different types of food for a preterm baby in the neonatal intensive care unit (NICU):
- Mother’s milk
- Donor milk from a human milk bank
- Combination of mother’s/donor milk and formula
Several studies have shown that mother’s milk is the best form of nutrition for term and preterm born infants. If mothers cannot provide enough breast milk, it can be supplemented with donor milk from an established human milk bank that follows specific safety regulations or a preterm infant formula.
Even though early preterm milk has a higher protein content, it is still not sufficient for the high needs of many of these infants and normally needs to be fortified with additional nutrients, in particular protein, calcium and phosphorus, to meet the baby’s increased needs. It is well tolerated and digested in preterm babies and results in faster weight gain.
Breast milk for preterm babies
Preterm infants have higher nutrient requirements than term infants. One reason is that they miss the third trimester of pregnancy which is the intended period of nutrient accumulation and rapid growth. During this time period the foetus swallows around 750 ml of amniotic fluid every day supporting the development of the digestive tract. The digestive tract of preterm babies is immature and functions such as intestinal movements, secretion of protective digestive substances and the digestion and absorption of food are reduced. Mother’s milk is the most suitable food for these babies, too, because of many protective enzymes, hormones and growth factors that play important roles in gastrointestinal development and maturation.
Preterm infants have higher nutrient requirements than term infants. One reason for this is that they miss the third trimester of pregnancy which is the intended period of nutrient accumulation and rapid growth. During this time period the foetus swallows around 750 ml of amniotic fluid every day supporting the development of the digestive tract. The digestive tract of preterm babies is immature and functions such as intestinal movements, secretion of protective digestive substances and the digestion and absorption of food are reduced. Human milk is the most suitable food for these babies because it contains many protective enzymes, hormones and growth factors that play important roles in gastrointestinal development and maturation.
Depending on gestational age, preterm infants may benefit less from the transfer of antibodies across the placenta during the last period of pregnancy. However, they can still receive antibodies through feeding with mother’s milk. The immunologic aspects are especially relevant for preterm infants who are at a higher risk for infections. Additionally to all positive effects of breast milk for newborns, studies report reduced risk of respiratory infections (e.g. lung inflammation), sepsis (blood poisoning), and necrotizing enterocolitis (NEC) (disease of the intestinal tract, caused by inflammation or decreased blood supply to the bowel) in breastfed preterm babies.
As preterm babies were not able to get the necessary time to develop and grow in the womb of their mothers, they may need nutritional supplements in addition to breast milk for a limited time.
Brain, lungs and kidneys are still developing and therefore need adequate nutrition. Extra protein will be added to sufficiently support the development of the brain and to achieve the best growth in length and weight. The growing bones also require minerals like calcium and phosphorus. These supplements are especially important for preterm infants because they missed the normal period of accumulation of these minerals in the third trimester of pregnancy.
These extra nutrients will be added to the milk before it is fed to the baby, e.g., through a feeding tube (small tube to provide nutrition to neonates, who are not able to suck and swallow on their own). They can be added individually to the milk or can be provided by using commercially available liquid or powdered fortifiers which combine several extra nutrients to enrich breast milk.
Nutritional needs of the baby are assessed by healthcare professionals at the neonatal intensive care unit (NICU) and they decide together with parents what is best for the individual preterm infant.
In some cases, it may not be possible to provide a sufficient amount of breast milk. In these cases, special formulas for preterm infants are available. These special formulas contain higher energy, proteins and minerals than formula for babies born at term in order to meet their growth requirements.
Expression of milk
Breastfeeding can be challenging for parents of a preterm baby, because preterm babies may not be able to drink directly from the breast.
Therefore, expression of milk is the best solution to offer mother’s milk to a baby until breastfeeding is achievable.
Frequent expression of breast milk shortly after delivery maximises milk supply and supports the development of colostrum to transitional milk and mature milk. Mothers of preterm babies should be made aware that they will not produce a lot of milk immediately. It takes time for the milk supply to build up. Important is to continue stimulating the breast and to pumping milk regularly. Even though the quantity of milk produced seems low, at the beginning, every drop of milk is important for the baby and the quantity will increase over time.
Colostrum can be obtained directly after birth by massaging the breast or by using a breast pump. According to experts, milk should be expressed regularly every 2 to 3 hours and at least 15 minutes in the days and weeks following delivery to stimulate milk production.
Practicing kangaroo care before or during milk expression can improve the amount of milk. If skin-to-skin contact is not possible also looking at the baby or even a picture might stimulate the milk production.
Methods of milk expression
There are different opportunities for mothers to express breast milk.
can be taught by a lactation specialist. Milk can be effectively expressed, collected in a clean container and stored afterwards. There is no need for a pump or electricity, so that mothers can express their milk any time and place (even though it takes some time).
Mother’s milk can also be expressed by manual or electrical milk pumps.
Manual milk pumps
can be used without electricity just by effort e.g. by pressing a lever. They are lightweight and portable. Nevertheless, it can be quite tiring, if a mother needs to express her milk on a daily basis. But they are a very good option for pumping milk when there is no access to electricity or an electric milk pump.
Electric milk pumps
can be used as single or double pump.
Research has shown that using a double pump is more effective for milk production and that milk expressed by double pumping provides a higher fat level comparing to milk expressed by a single pump. It is also less time consuming as both breasts can be expressed simultaneously.
Hygienic aspects should be considered for optimal storage and transport of expressed breast milk. Milk pumps should be used with sterile expressing sets and bottles which are provided by hospitals. Transferring of milk from one container to another increases the risk of contamination. Parents should ask health professionals or a lactation specialist for the latest guidelines on the storage of breast milk in refrigerators. Cooling bags with cooling elements between the bottles are the best option for transporting expressed milk and for ensuring the continuous cold chain. When feeding the milk to a baby, it should be as fresh as possible and must not be at room temperature for more than 4 hours. The milk must not be at room temperature for more than 4 hours. Also personal hygiene, such as washing hands before expressing the milk or taking a shower regularly is necessary for clean breast milk.
Health professionals or lactation specialists at the hospitals can help to discover the best solution for parents to provide milk for their baby.
The aim of nutritional support for a preterm baby is to achieve a similar growth rate compared to the foetus at the same age. In order to reach the optimal development experts recommend to start feeding as soon as possible after birth. However, it may not always be possible to start full feeding immediately after birth.
might be necessary in the beginning, if the intestines cannot yet tolerate any food. Preterm infants receive all important nutrients such as carbohydrates, electrolytes, protein, minerals, vitamins, and fat as well as liquid through a venous catheter without using the digestive tract. Parenteral nutrition may also be combined with enteral feeding. Studies provide evidence that early parenteral nutrition reduces the time to regain birth weight and improves weight at discharge.
means feeding the baby by using a nasogastric (via nose to stomach) or orogastric (via mouth to stomach) tube. It can be initiated as soon as the gastrointestinal tract is mature. This solution is recommended by most guidelines for preterm infants as long as they cannot coordinate to drink, suck, swallow and breathe. The ability for suck-feeding usually develops around 35 weeks of gestational age, so that infants born before 35 weeks will most likely require temporary tube feeding. During the first days of life, only very small amounts of milk are administered until the intestines get used to it.
The first steps towards breastfeeding can be initiated as soon as the condition of the preterm baby has stabilised. The learning process takes time and needs a lot of patience. The first step towards breastfeeding is kangaroo care which may already be commenced soon after birth. Health care professionals together with parents will decide if the preterm baby is stable enough for kangaroo care. Skin-to-skin contact will help the baby to develop the feeding abilities and also stimulates the milk production.
Around the age of 24 weeks, babies are able to do their first sucking movements but cannot coordinate sucking and swallowing yet.
Between 26 and 30 weeks the development progresses and babies will have a gag reflex, which helps to prevent choking. At this stage, some babies are already able to lick some drops of breast milk.
In the next two weeks, kangarooed infants will already start to turn their head towards the breast and may lick some drops of milk directly from the breast. But most feeds will still need to be through the nasogastric tube.
The ability to coordinate sucking, swallowing and breathing will be developed around the age of 35 weeks. But most infants at that age are still weak and may get tired easily. Hence, tube feeding is still needed in many cases.
The preterm infant will now get more active every day until even full breastfeeding is possible. Some hospitals work with so-called ‘early feeding scales’ for the assessment of feeding abilities or nutrition specialists check whether a preterm baby is ready to start oral feeding.
Babies may also need temporary support such as nipple shields, finger feeding, cup feeding or bottle feeding. There are numerous techniques for feeding a preterm baby with breast milk. Healthcare professionals or lactation specialists can help parents to find the optimal solution for them and their baby.
Cytomegalovirus (CMV) is a virus that persists lifelong in blood cells and approximately half of all adults are carriers. The virus can be reactivated in mothers during the lactation period and can be transmitted to the infant via breast milk.
In general, infections in term infants stay asymptomatic because of the transmission of protective maternal antibodies in the last trimester of pregnancy. Very preterm born infants cannot be protected by these antibodies and are therefore at higher risk for symptomatic CMV. Although it is very unlikely, CMV can affect the clinical course of pre-existing diseases in preterm infants. Nevertheless preterm infants benefit from mother’s milk so that several experts still recommend breastfeeding for CMV-positive mothers. Pasteurisation is effective in deactivating the virus in breast milk and can also be a solution for preterm infants. It is recommended, that CMV-positive mothers and healthcare professionals discuss together the best solution based on the health status of the baby.
When providing milk is not possible
If mothers cannot provide enough milk, they should discuss alternative feeding options with a healthcare professional or a lactation specialist. Some guidelines recommend to express milk more often or to place warm compresses around the breast before milk expression. Specialists can also teach how to massage the breasts to intensify the blood circulation and activate milk ejection reflex. In addition, kangaroo care or any skin-to-skin contact will support mothers to provide more milk to their babies.
In case of insufficient breast milk, the milk can be supplemented with donor milk from an established human milk bank which follows specific safety guidelines or a preterm infant formula.
A human milk bank collects, screens, stores, processes and distributes donor breast milk. Women donating milk will require a series of screening tests to make sure that they are physically healthy.