4.2 Milk production

Key Points
Sally is 29 years old and presents to see you two and a half weeks postpartum with her first baby. Emily was born at T+7 days and weighed 4060 grams. Sally had a normal delivery but had a postpartum haemorrhage and a retained placenta that required a general anaesthetic and manual removal. They were discharged on day three fully breastfeeding, with Emily weighing 3770 grams and Sally's Hb 92 g/L. Sally has no other significant medical or surgical history, is well educated and has a supportive partner. Emily is a "good" baby: she is sleeping at least six hours at night and seems content. What questions would you ask Sally, and what additional information would you gather to assess whether breastfeeding was progressing normally?
- Topic 4.1: Initial assessment
- To assess the adequacy of breast milk intake ask about: number and length of feeds; elimination patterns; general infant behaviour; breast and nipple concerns; and maternal confidence. Also check: infant weight gain; jaundice and general infant wellbeing.
Sally is confident with her breastfeeding and her breasts and nipples are fine. Her breasts feel a little fuller early in the morning, but she has not had problems with engorgement like some of her friends. Emily is feeding approximately six times a day and feeds for 15-20 minutes before falling asleep. She is having four wet nappies a day – two of which are damp. She is having a bowel motion every three days or so. Emily weighs 3800 grams. On examination, she is not dehydrated. You are concerned that Emily is not getting enough breast milk.
- Topic 4.2: Milk production
- Oxytocin and prolactin are the main hormones necessary for the initiation of lactation. Factors such as diabetes, primiparity, caesarean section, stress and pain in labour, obesity and preterm delivery can interfere with the onset of lactation. Once lactation is established, milk removal is the main determinant of milk production.
Sally is confident with her breastfeeding and her breasts and nipples are fine. Her breasts feel a little fuller early in the morning, but she has not had problems with engorgement like some of her friends. Emily is feeding approximately six times a day and feeds for 15-20 minutes before falling asleep. She is having four wet nappies a day – two of which are damp. She is having a bowel motion every three days or so. Emily weighs 3800 grams. On examination, she is not dehydrated. You are concerned that Emily is not getting enough breast milk.
What initiates and controls milk production?
Hormones necessary for the development of the breasts during pregnancy and the subsequent secretion of colostrum and milk include (but are not limited to) placental lactogen, oestrogen, progesterone, prolactin, glucocorticoids, thyroxin and growth hormone.
During the first half of the pregnancy, mammogenesis occurs with growth and proliferation of the TDLUs, resulting in an increase in breast size for most women. Continued growth occurs during the second half of pregnancy, along with the differentiation of alveolar cells into lactocytes and the production of small quantities of secretion (colostrum) (secretory differentiation/lactogenesis I).1,2 High oestrogen levels during the pregnancy stimulate the release of prolactin. However, progesterone inhibits the effect of prolactin on the lactocytes and thus production of milk. Nevertheless, colostrum production is related to prolactin levels. Junctions between the lactocytes are not tightly closed during pregnancy, enabling lactose secreted into the alveoli to enter the maternal bloodstream and be excreted by the kidney. Urinary lactose levels indicate secretory differentiation has occurred and have been used to calculate the amount of colostrum produced each day (30mls)3. As the breasts are capable of producing milk from the middle of pregnancy, delivery of the foetus/infant from that time will result in an increase in milk production – often an unexpected and unwanted development if the pregnancy ends in miscarriage or the infant is not viable.
In the presence of high levels of prolactin and with a primed mammary epithelium secretory activation (lactogenesis II), the onset of copious milk production, begins with the delivery of the placenta and the subsequent drop in progesterone levels4. The tight junctions between lactocytes close, preventing the passage of molecules from the maternal circulation to alveolar spaces and resulting in an increase in lactose and a decrease in sodium and chloride levels in the milk secreted. As secretory activation progresses, the fat levels increase, as does the concentration of citrate, potassium, casein, calcium and phosphate1. Concentrations of Secretory IgA and lactoferrin also rise during the first 48 hours, but then fall – mainly due to an increase in milk volume rather than a decrease in the total amount secreted. Copious milk production begins around 36 hours postpartum with the volume increasing up to ten times over the next 36 hours. Lactose synthesis largely determines the volume of milk produced as its osmotic activity draws water into the lactocytes and thus to milk2. Women experience this increase in milk volume as "milk coming in"5.
Although secretory activation is primarily hormonally driven, regardless of milk removal, there is some evidence that early, frequent feeding increases subsequent breast milk volumes and it is hypothesised that for some women milk removal is necessary for closure of the tight junctions4. Regardless, by day three milk removal is essential for continued milk production.
Prolactin is produced by the anterior pituitary gland under the control of the hypothalamus. In response to tactile stimulation of the nipple (usually the infant breastfeeding), levels rise, peaking after 25 to 40 minutes and returning to resting levels by 180 minutes6. Both resting levels and suckling-evoked peaks are highest in the first month or so after birth, and then gradually fall so that by six months postpartum the resting levels are only slightly higher than those of non-lactating women7, although milk volumes appear unaltered. Therefore, while prolactin is essential for the initiation of lactation, it is not the main determinant of ongoing milk production.
Oxytocin, an octapeptide produced by the posterior pituitary, is released in a pulsatile fashion in response to the infant suckling at the breast. Oxytocin causes contraction of myoepithelial cells surrounding the mammary ducts, resulting in shortening and widening of the ductal structures and expulsion of milk through the nipple. This reflex, called the milk-ejection or let-down reflex, is essential for the removal of milk already stored in the breast. It can be conditioned so that seeing the infant, or hearing the infant cry in preparation for a breastfeed, results in a rise in oxytocin levels8 and in a milk-ejection. Conversely, the milk-ejection reflex can be inhibited by stimuli such as pain and other stressful events (6,9). Mothers often recognise milk ejection by a tingling sensation in the breast soon after the infant begins to feed, milk dripping from the "other" breast, or a change in the infant's sucking pattern.
Risk factors for a delay in Secretory Activation
Click on the bullet points below for more detail:
- Diabetes
- Women with IDDM have a delay in the onset of copious milk production of approximately 28 hours, although their milk volumes by day seven are within the normal range. As insulin is necessary for lactogenesis and glucose is an important substrate for milk production, it is uncertain whether women with poorly controlled diabetes are more at risk. 10 11 There does not appear to be a similar delay in women with gestational diabetes. 11
- Primiparity
- Cesarean section
- After adjusting for timing of the first feed and other confounders, the amount of milk an infant delivered by caesarean section receives during the first six days of life is less than that received by infants delivered vaginally 16 . Other studies have also noted a delay in the onset of milk production for women who have undergone caesarean section 12 , especially if the caesarean section was unplanned 17 .
- Stress and pain in labour
- Difficult and protracted labours, especially with a long second stage, have also been associated with a delay in secretory activation. 17
- Obesity
- Preterm delivery
- Women who deliver prematurely tend to have a delay in secretory activation and produce less milk than women whose infants are born at term. 20 This effect is often thought to be due to the differences in both the frequency and mechanism of milk removal. However, 82 percent of women who delivered prematurely had at least one of four markers for secretory activation outside the normal range on day five (compared with no abnormal markers for women who delivered at term). 21
- Postpartum hemorrhage
- Women who have had a large postpartum haemorrhage (>3000ml) are more likely to have difficulty initiating lactation and are less likely to be breastfeeding at two and four months. 22
After the initiation of lactation, the most important determinant of ongoing milk production is milk removal. Short-term milk synthesis rates are related to the degree of fullness of the breast so that milk is made at a much faster rate when the breasts are drained, compared with when they are full23. The daily amount of milk a mother makes will be determined by the frequency with which her infant feeds, and the degree of breast emptying at each feed (i.e. the infant's appetite).
There is great variation between mothers in the amount of milk each breast is able to store (e.g. 74 to 382 mls)24. The infants of women with small storage capacities will tend to remove all or most of the available milk at each feed and feed more frequently1, while infants of mothers with large storage capacities may only remove a proportion of the milk available even though they may consume more milk per feed. On average, infants do not remove all available milk at each feed24. The differences in storage capacities between mothers helps explain the differences in feeding patterns between mother-infant couples – including the number and timing of feeds, and whether the infant feeds from one or two breasts at each feed. Therefore, watching for feeding cues and following the infant's lead regarding the pattern of feeding is the most appropriate way to ensure adequate milk production and infant growth.
Case Study Activity
Notes
- # Kent JC (2007) How breastfeeding works
- # Czank C et al. (2007) Hormonal control of the lactation cycle
- # Cox DB et al. (1999) Breast growth and the urinary excretion of lactose during human pregnancy and early lactation: endocrine relationships
- # Neville M et al. (2001) Physiology and Endocrine Changes Underlying Human Lactogenesis II
- # Neville M et al. (2001) Lactogenesis: The transition from pregnancy to lactation
- # Hartmann PE et al. (1995) Endocrine and autocrine strategies for the control of lactation in women and sows
- # Cox DB et al. (1996) Blood and milk prolactin and the rate of milk synthesis in women
- # McNeilly A et al. (1983) Release of oxytocin and prolactin in response to suckling
- # Ueda T et al. (1994) Influence of psychological stress on suckling-induced pulsatile oxytocin release
- # Arthur PG et al. (1989) Milk lactose, citrate, and glucose as markers of lactogenesis in normal and diabetic women
- # Hartmann P et al. (2001) Lactogenesis and the effects of insulin-dependent diabetes mellitus and prematurity
- # Dewey KG et al. (2003) Risk factors for suboptimal infant breastfeeding behavior, delayed onset of lactation, and excess neonatal weight loss
- # Nommsen-Rivers LA et al. (2010) Delayed onset of lactogenesis among first-time mothers is related to maternal obesity and factors associated with ineffective breastfeeding.
- # Hill PD et al. (2005) Primary and secondary mediators' influence on milk output in lactating mothers of preterm and term infants
- # Ingram J et al. (2001) Breastfeeding: it is worth trying with a second baby
- # Evans K et al. (2003) Effect of casearean section on breast milk transfer to the normal term newborn over the first week of life
- # Chapman D et al. (1999) Identification of risk factors for delayed onset of lactation
- # Wojcicki JM (2011) Maternal prepregnancy body mass index and initiation and duration of breastfeeding: a review of the literature.
- # Oddy WH et al. (2006) The association of maternal overweight and obesity with breastfeeding duration
- # Henderson JJ et al. (2008) Effect of preterm birth and antenatal corticosteroid treatment on lactogenesis II in women.
- # Cregan MD et al. (2002) Initiation of lactation in women after preterm delivery
- # Thompson JF et al. (2010) Women\'s breastfeeding experiences following a significant primary postpartum haemorrhage: A multicentre cohort study.
- # Daly SE et al. (1993) The short-term synthesis and infant-regulated removal of milk in lactating women
- # Kent JC et al. (2006) Volume and frequency of breastfeedings and fat content of breast milk throughout the day