As survival rates for preterm infants improve, attention is focused on improving the quality of survival through nutritional management. Necrotising enterocolitis (NEC) remains one of the most critical complications. Although no individual randomised controlled trial (RCT) has been sufficiently powered to examine the true effect of breast milk on the incidence of NEC in preterm babies,¹ a series of observational studies and a meta-analysis suggest a reduced incidence in those fed breast milk.^2–5 There is also evidence that human milk is better tolerated than formula, leading to a faster attainment of enteral feeding.⁶

Mothers of preterm infants experience physiological and emotional challenges, which may adversely affect breast feeding outcome following delivery. Therefore, it is not surprising that these mothers start and sustain breast feeding at lower rates than mothers of term babies.⁷ This is further compounded by the high levels of socioeconomic deprivation common in this population.⁸ Although there is a marked inverse relationship between gestational age and duration of breast feeding, it is not inevitable that lactation should fail, even in mothers of extremely low birthweight infants.⁹ This paper discusses the possible implications of a shortened pregnancy on mammary physiology and the lactating breast, and how to deal with any issues this might pose about the management of milk expression.

PHYSIOLOGY OF PRETERM LACTATION

Preterm delivery adversely affects initiation of lactation for the following reasons:

• mammary growth may be incomplete in a substantially shortened pregnancy, and poor placental function with low levels of placental lactogen may exacerbate this problem further¹⁰;

• the mammary epithelium may not be sufficiently prepared by the hormones of pregnancy to respond with efficient milk synthesis¹¹;

• lactation may be inhibited by stress, fatigue and anxiety.¹²

Although some mothers lack the capacity to respond to the stimulation of milk expression and have diminished milk production, others seem to achieve compensatory growth by the adoption of a frequent milk expression schedule in the early postpartum period.¹⁰ As the average baseline milk production on days 6–7 is highly predictive of adequate milk volume (defined as greater than 500 ml/day) at six weeks post partum, mothers of extremely preterm infants should be taught effective milk expression techniques as a matter of urgency.¹³

ENCOURAGING MOTHERS TO PRODUCE MILK

A protocol should be in place to ensure the role of expressed breast milk in the care of the premature infant is discussed with all expectant mothers during the antenatal period. This also provides an opportunity for anticipatory guidance about the importance of early, frequent milk expression. It is helpful to reinforce the verbal discussion with written information about the benefits of breast milk and the principles of milk expression.

Following the birth of a preterm infant, the importance of human milk feeding should be discussed with the parents during the first visit to the unit by neonatal staff. Counselling mothers at this stage increases the incidence of lactation initiation and contrary to popular belief does not increase maternal stress or anxiety.^14,15 When a mother and baby are separated, the health professionals caring for the baby should liaise with staff caring for the mother to ensure that the she has been given support to start a milk supply. The premature charity BLISS has produced a parent information leaflet entitled Breastfeeding your premature baby, which is available for distribution in the UK. It should be given to all mothers of preterm infants at an early stage.¹⁶

OPTIMISING LACTATION SUCCESS

It is important that the first milk expression should take place as soon as possible following delivery.^8,17 Mothers should be given realistic expectations regarding the initial milk volume because the amount produced can be as little as a few drops of colostrum at each expression for the first 24–48 hours post partum. There may be a considerable delay before more substantial milk production begins. Mothers should be encouraged to express at least eight times in 24 hours, because any break in the frequency of effective milk removal at this time may seriously compromise the potential to maximize milk production¹⁸ It has been shown that mothers of very low birthweight (VLBW) infants who produce adequate milk volumes at five weeks post partum pump at least 45 times per week (more than six times a day).¹⁹ The goal is to establish a milk supply of at least 750 ml/day by day 10, because milk production, the most powerful determinant of lactation success, typically plateaus by two weeks post partum.²⁰ When the milk supply is low at day 10 (less than 350 ml/day) despite frequent milk expression, it is important to ensure that the milk expression technique is optimal. This includes:

• a supportive environment for the mother;

• regular breast massage using a good technique;

• simultaneous pumping of both breasts;

• use of a high-quality breast pump;

• a properly fitting milk expression shield.

Usually these measures, which are discussed in detail below, will rescue the situation, but if not then the pharmacological enhancement of prolactin secretion may have some value. Domperidone or metoclopramide may increase milk supply in the short term.^21,22 However, these medications are not licensed to augment lactation and there is no evidence-based protocol for drug timing and dosage.

PRACTICAL MEASURES

The process by which milk is expelled from the alveoli is called the milk ejection reflex and is essential to milk removal from the lactating breast. When this reflex is inhibited, the average milk yield is less than 4% of available milk, and local mechanisms bring about an inhibition in milk secretion.²³ In stressful situations, mothers may have difficulty with milk ejection when expressing. The early instigation of kangaroo mother care (KMC) is thought to be beneficial in this respect, with mothers experiencing feelings of milk ejection during KMC (fig 1).²⁴ It has been shown that mothers of VLBW infants who practised KMC lactated on average four weeks longer than controls,²⁵ with less chances of discontinuing lactation before discharge.²⁶ In contrast, the use of nasal oxytocin spray does not markedly improve the milk yield during the first five days post partum.²⁷

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Figure 1

 Kangaroo Mother Care (KMC). Informed consent was obtained for publication of this figure.

Milk expression is more likely to be effective using a high-quality electric breast pump with the following characteristics²⁸:

• easy to assemble and disassemble with all parts able to withstand sterilisation methods;

• fully automatic, with a cyclic suction rhythm that mimics infant suckling;

• vacuum strength that does not exceed 250 mm Hg, and is easily regulated;

• separate drive and suction system to ensure that no contamination from milk spillage can enter the pump;

• a system of collection that allows milk to be pumped directly into a storage container with a universal thread, to avoid the need to transfer milk to another container for storage or administration.

Breast massage is a highly effective technique for stimulating milk ejection and should be used before starting to express.²⁹ A good massage technique involves stroking the breast with gentle feather-like movements, or using a hand action that rolls the knuckles downwards over the breast, beginning at the top of the breast and working towards the areola. Rolling the nipple gently between the thumb and forefinger or stroking the nipple with the palm of the hand is also beneficial. The massage should be completed by stroking the area under the nipple and areola with flat hands in an upward movement.

Double pumping requires two breast shields and collection sets. A mirror can be used to ensure that the shields are placed with the nipples central. Light pressure is required to obtain a patent seal—firm pressure will inhibit milk flow as the ducts are easily compressed. It is important not to force the rim into a section of the breast and obstruct drainage from the area. A specially adapted bra is available which holds both collection sets securely, allowing the mother to pump hands free.¹⁶

Finally, we have observed that the diameter of the aperture of the milk expression shield can affect milk output, because shields that are too small compress the milk ducts, inhibiting milk flow. As the main culprit for sore nipples during milk expression is the use of an undersized breast shield, a variety of sizes should be available. The most appropriate size is usually determined by comfort.

CONCLUSION

The most common misconception that undermines successful lactation for mothers of preterm infants is that initiation of milk expression can be delayed until an infant is stable. To overcome this problem collaborative guidelines should be in place so that midwives and neonatal nurses can work together to ensure the early establishment of frequent milk expression. Furthermore all healthcare professionals who care for preterm infants should have expert knowledge of mammary physiology and management of milk expression. This requires a comprehensive training programme such as the one currently recommended by the UK Department of Health.³⁰

A mother’s commitment to supplying her milk will probably have considerable medical benefit for a VLBW baby, both in the short and long term. If the principles of milk expression outlined above are followed, there will rarely be a need to resort to bank milk. In most instances, successful expression in the early stages will lead to successful preterm breast feeding, which should be the ultimate goal.