WHY DO WE MAKE MILK?
So why does human milk matter for infants and new parents? Human milk feeding, whether by a chest, breast, or bottle, is the normative standard for infant nutrition and not simply a lifestyle choice. National rates of any and exclusive breastfeeding have been steadily increasing since the 1970s, and families look to health care providers for support and advice on infant feeding.
Since many of us did not receive any formal medical education on human milk and lactation, it's often our own experiences, whether positive or negative, that inform the advice that we give to patients. Like any other area of medicine, our goal should be to provide evidence-based information on the science and health impacts of human milk feeding and to support families in identifying and helping them to reach their personal infant feeding goals.
WHAT EXACTLY IS THE “MILK” THAT COMES OUT WITH NURSING?
Human milk is a dynamic, complex fluid that contains not only nutrients but also bioactive factors that are needed for infant health and development. Its composition changes over the course of feeding day-to-day, and over the first year of life, to meet the changing growth needs of the infant.
COLOSTRUM
Colostrum produced in the first three to four days is particularly rich in protein, antibodies, and beta carotene, which are important for host defense during that unique and vulnerable period of time.
PROTEIN
The protein content of human milk differs pretty significantly from cows. Human milk is 70% whey and 30% casein, whereas cow’s milk is predominantly casein. And this makes a difference because whey is digested much more easily than casein.
And the protein components of human milk include not only nutritive amino acids but immunoglobulins, lysozyme, lactoferrin, amylase, lipase, insulin, and growth factors. In particular, human milk’s lactoferrin, lysozyme, and secretory IgA are specific to human milk and are really important for lining the gastrointestinal tract to provide that first-line host defense against pathogens.
LACTOSE
The primary carbohydrate in human milk is lactose. About 5-10% of that carbohydrate is a very specific type of carbohydrate called a human milk oligosaccharide, of which there are more than 100 different types and they are specific to human milk.
HMOs
HMOs act as prebiotics and they stimulate intestinal colonization with lactobacillus and bifidobacteria species and reduce the pathogenic bacterial colonization with E. coli and other microbes.
LIPIDS
Lipids compose 50% of the calories in human milk. In particular, arachidonic acid, or ARA and DHA, are specific to human milk and are very important for retinol and neural tissue development. The lipid content of human milk actually increases two to threefold from the beginning to the end of a feed, so that can make a difference as well.
CALORIES IN BREASTMILK
In terms of calorie intake based on maternal-infant feeding behavior, human milk, in particular, is low in calcium, phosphorus, iron, zinc, vitamin K, and vitamin D, thus we supplement babies right at birth with vitamin K. We recommend vitamin D supplementation through the first year as long as mom is breastfeeding and iron supplementation for infants after six months of age.
WHY BREASTMILK IS GOOD FOR BABIES
There are some really important bioactive factors in human milk that can never be replicated in infant formula. Some of those are cytokines, various growth factors, enzymes, nucleotides, antioxidants, and hormones like insulin, leptin, and adiponectin.
Human milk also amazingly contains macrophages, lymphocytes, neutrophils, nucleotides, and even stem cells. So when a mother is exposed to foreign antigens via her gastrointestinal or respiratory tract, she produces secretory IgA that's specific to that antigen exposure and is secreted at mucosal surfaces throughout the body, including in the mammary glands.
And so ingestion of human milk provides the infant with passive secretory IgA antibodies within 3-4 days of maternal antigen exposure. The skin-to-skin contact of the breastfeeding mother and infant is thought to facilitate this relationship.
And during active infection in nursing infants, macrophages and TNF-alpha levels actually increased in the mother's milk. Human milk feeding has been associated with a reduced risk of atopic diseases. The growth of the lactobacillus and bifidobacterium species in the metabolism of these particular types of bacteria actually influences immune system maturation.
For example, this milieu can cause upregulation of regulatory T cells that promote oral tolerance. And it can also induce the production of IL-22, which impacts gut maturation.
THE SHORT & LONG-TERM BENEFITS
So you're likely familiar with some of the short and long-term health benefits of mother's milk for infants. These are dose and duration-dependent, such that increased duration and exclusivity of breastfeeding confers greater protection.
These outcomes include a lower risk of upper respiratory tract infections, lower respiratory tract infection, otitis media, asthma, atopic dermatitis, necrotizing enterocolitis, gastroenteritis, inflammatory bowel disease, celiac disease, obesity, Type 1 and Type 2 diabetes, ALL, AML, and SIDS.
In addition to these infant health outcomes, mothers who breastfeed for at least 12 cumulative months over their childbearing years have about a 26% reduced risk of breast cancer, a 37% reduced risk of ovarian cancer, and a 32% decreased risk of Type 2 diabetes.
So with so many really amazing and documented health benefits for infants and mothers, why is it that so many families continue to use cow's milk-based infant formulas to feed their infants?
WHY DO MANY PEOPLE USE REGULAR MILK INSTEAD OF BREASTMILK?
Well, in many cases, it's a personal choice, or in some cases, there are contraindications to human milk feeding. But for the vast majority of families, it really comes down to barriers to breastfeeding in the U.S.
And these are so pervasive that actually about nine years ago in 2011, the Surgeon General published a call to action to support breastfeeding and, along with the CDC and the World Health Organization, has made promotion and protection of breastfeeding a high priority.
Some of these barriers include a lack of public knowledge about the benefits and maintenance of breastfeeding, social norms that favor formula feeding, poor family and social support, embarrassment around feeding in public or even incidences of public shaming, lactation difficulties, employment, and childcare barriers, and barriers related to health care services.
We as maternal-child health care providers can support families that are choosing to breastfeed.
Overall, the rates of breastfeeding in the U.S. are actually relatively high when we look at breastfeeding initiation at delivery. About 82% of children born in 2016, for example, received at least some breast milk prior to hospital discharge, and about 65% were exclusively breastfed. With each subsequent week and month, however, those rates drop off pretty precipitously, such that at six months, only about 25% of children are still being exclusively breastfed, which is the recommendation of the American Academy of Pediatrics.
So another way to look at this data is to note that most women are intending to breastfeed at the time of delivery, but about 60% of mothers who stop breastfeeding do so earlier than they had originally intended to. Really, the things that impacted not meeting one's personal goals included reporting difficulty with latch, nipple trauma or pain, engorgement, mastitis, a perception of insufficient milk supply, mother's concern or family's concern over insufficient infant weight gain, and maternal medication use.
And it's important to note that these are all really common issues that are very preventable with education, particularly, in the prenatal period, and with skilled perinatal health care provider support. So, next, I'd like to just briefly review the anatomy and physiology of human lactation.
THE ANATOMY AND PHYSIOLOGY OF HUMAN LACTATION
So the human mammary gland is really the only organ that's not fully developed at birth, and it only reaches full maturity during pregnancy. It's a compound tubuloalveolar gland with 15-25 lobes that radiate from each nipple. The ducts and the little ductules consist of an inner lining of epithelial cells and an outer lining of myoepithelial cells.
So then, when we think about lactogenesis, which is really the stage of milk production, there are two stages. The first starts around 16 weeks of pregnancy and involves the cellular differentiation of the alveoli epithelial to secretory cells. And this development is stimulated by prolactin and human milk lactogen.
And the high levels of progesterone during pregnancy prevent actual milk production during that time. Stage two, then, after delivery is marked by that rapid drop in the progesterone with the delivery of the placenta, and that stimulates that onset of the copious milk production within about two to four days after delivery.
So one really important factor to remember is that if colostrum or milk are not removed from the breast, the glands become distended, and there is actually an increase in something called feedback inhibitor of lactation, which then causes a negative feedback loop and down-regulates milk production to prevent massive overextension of the gland.
And so this will become critical when we are counseling families in the first days after delivery and down the road in terms of that frequent nursing, frequent removal of milk being so important for establishment and maintenance of lactation.
THE NIPPLE
The nipple contains smooth muscle fibers and is really richly innervated with sensory nerve endings that are important for the normal milk ejection reflex. And that is important because in cases where there may have been breast augmentation, for example, if there's a periareolar incision that's used, that can actually sever or damage the cutaneous branch of the fourth intercostal nerve, and that can impact those afference stimuli that impact the milk ejection reflex.
So, in terms of physiology, milk is really continuously synthesized and secreted into the lumen of the alveoli, where it's then stored. When the infant nurses the breast, there's an afferent sensory input that goes to the hypothalamus, which then causes a release of prolactin from the anterior pituitary and that causes milk secretion.
At the same time, oxytocin is released from the posterior pituitary and that causes smooth muscle contraction of the myoepithelial cells surrounding the alveoli and ducts, resulting in the milk let-down reflex.
WHAT HAPPENS TO THE MOTHER IN BREASTFEEDING?
One thing that's really interesting that some have likely experienced is that the higher brain centers regulate that hypothalamic control of oxytocin and prolactin secretion and respond to the sound of a baby crying, whether it's yours or another person's child while you're nursing and even thinking of one baby can actually cause that the milk let-down reflex.
Alternately, stress, pain, fatigue, anxiety: can all inhibit oxytocin release and lead to decreased milk output. Alcohol and opioids can also inhibit oxytocin release. While most women with adequate support are able to produce sufficient milk for their infant and have very few difficulties, there is a growing subpopulation of women who are at risk for either delayed or insufficient milk production.
And many of these women really can be identified through a lactation-focused history and physical exam, a breast exam during the prenatal period.
Because many women, although many have decided either before pregnancy or early in the pregnancy what their intentions are for infant feeding, those regular prenatal visits really provide an amazing opportunity for ongoing exploration of goals and barriers to provide support and education and to again, proactively identify those women that may be at risk for breastfeeding difficulties and connect them early on with skilled lactation support.
HOW TO KNOW IF YOUR PATIENT IS AT RISK OF COPIOUS MILK PRODUCTION?
We know that the advice of a trusted health care provider does influence mothers' decisions regarding breastfeeding. And if ambivalence is expressed, a motivational interviewing approach can be really helpful in terms of exploring that ambivalence over subsequent visits, a lactation-focused history, and breast exam can identify women at higher risk for delayed lactogenesis II, or that copious milk production.
So if we identify these risk factors, that information can be used to guide individual decision-making, and plan, refer to specialists, and most importantly, setting realistic expectations, which can be very important for managing some of the stress and anxiety around breastfeeding right after delivery.
So in terms of that lactation-focused history, there's certainly absolute contraindications to breastfeeding. For example, active maternal HIV infection in the United States in particular or in other developed countries. If a mother has an active, untreated tuberculosis infection, or if she has active HSV lesions on the breast, in particular, those are all contraindications to breastfeeding.
However, there are other kinds in particular of cardiometabolic factors that we think may impact milk production down the line. And so a history of PCOS, gestational diabetes, untreated hypothyroidism, infertility, and even advanced maternal age are not always but can be predisposed to more difficulty with milk production.
History of depression or anxiety is important to note, as those can impact infant feeding experience and how one manages that. And then, if you're anticipating a preterm delivery or a cesarean delivery, that may require some additional counseling in terms of what to expect after delivery. In particular, what to expect with preterm delivery, in terms of initial milk production and getting involved with a lactation consultant right away to get that started.
And with cesarean delivery, the fact that there can be a bit of a delay, about 24 hours in some cases in that lactogenesis II stage, or that feeling of milk coming in. In terms of breast exam, the exam should really note any breast asymmetry, significant breast asymmetry, hyperplasia of the breast, or tubular breast shape as those can be markers for underlying decreased glandular or milk-making tissue.
The provider should note any surgical scars related to breast augmentation, particularly in the periareolar region. One, because that can be a flag for a history of breast asymmetry or hyperplasia that might have led to the decision to undergo augmentation. And secondly, because that severing or damage of the fourth intercostal nerve, if that occurred, can impact the neuroendocrine response and that milk production and let-down reflex.
If any of these risk factors are identified, it's important to communicate to the mother that while we don't have a crystal ball, and many women with some of these factors go on to produce boat-loads of milk, she may have more difficulty with milk production than other women.
HOW TO TREAT A PATIENT WITH LACTATION DIFFICULTY
Then we start to reframe expectations and plan ahead so that she is able to meet her goals with our support backing her up. Some of the steps that you might take if you were to identify a woman that may be at higher risk for lactation difficulties would include a prenatal referral to an international board-certified lactation consultant to help plan for the postpartum period. Referral for prenatal breastfeeding, education classes.
And then one resource that a lot of providers are not aware of is that, actually, many county WIC agencies have a peer breastfeeding support program that is a wonderful, community-based resource for families, and they ideally start working with women in the prenatal period and then through delivery and until the mother decides to wean.
For all new mothers who are planning to breastfeed, it's so critical to provide that anticipatory guidance about what to expect in the first hour after delivery in the first 24, 48, 72 hours, and in the first week postpartum. Because particularly for first-time parents, this just really helps families better understand and respond to their newborns’ normal feeding patterns and cues and to reduce some of the stress and anxiety when a baby's behavior doesn't match their expectations.
PERINATAL PRACTICES THAT OPTIMIZE BREASTFEEDING’S CHANCES OF SUCCESS
You're likely familiar with the 10 steps to successful breastfeeding, which were developed by UNICEF and the World Health Organization for the Baby-Friendly Hospital Initiative. These 10 steps are all evidence-based practices that have been shown to improve breastfeeding rates at hospital discharge and beyond.
Of these, some of the steps that I've found to be the most important are highlighted here. I've found that most families have heard some version of the phrase, “Breast is Best,” and they're aware of some of the benefits to infants like reduced risk of ear infections. But few are aware of the benefits for maternal health.
And most first-time breastfeeding families have little to no prior knowledge of how to get a baby latched comfortably. How important that early and regular colostrum removal is for later milk production. How to remove colostrum from their breasts, or that the second-night feeding marathon, for example, is very normal newborn behavior.
This information really needs to be shared with families in the prenatal period to prepare them for what to expect in those first 24 hours. It's such a stressful period, regardless of what happens with the delivery. And so that is just not the time to be learning new information for the first time, and particularly for something that's as important as infant feeding and helping the family to meet their goals.
RESOURCES AVAILABLE TO NEW MOTHERS
When you have questions about lactation, Mayo Clinic actually has some fabulous lactation resources that are available to us. But I find that we're not all aware that they exist. So Mayo Clinics, Lactation Services Department actually have IBCLCs, or international board-certified lactation consultants, that are available not only in the hospital but also in the outpatient setting through the Department of Obstetrics and Gynecology for prenatal visits.
Postpartum visits can also be planned for those families that are needing more skilled support. Another really helpful resource to know about is that many of our primary care clinics actually have RNs that have additional training as CLCs, or clinical lactation counselors.
These nurses have gone through a training program to receive an extra 45 hours of didactic training, along with some clinical training as well, in order to be able to help families with some of the really common obstacles that come up in the first days and weeks of breastfeeding around the latch, positioning, providing education, general support to families, information about engorgement and how to prevent that.
And so I would encourage you to talk with your nursing leadership and find out whether you have a CLC who is available at your clinic, and how you might be able to integrate them into your visit with newborns and with their families.
If you don't have one available, find out where you know where that next resource would be. We have several primary care clinics in the Rochester area that have wonderful CLCs. And there's actually a really great Ask a Mayo Expert page. If you just enter breastfeeding, it lists a number of common issues that come up and you can search that.
And there's a list of resources, providers that are available as resources to you as well. That WIC peer breastfeeding counselor service is just a fantastic resource to know about. One of the main goals of the program is to improve equity and breastfeeding outcomes and reduce racial and ethnic disparities.
And so peers are ideally paired based on ethnicity or based on language in order to provide that really culturally specific peer-to-peer lactation support. This is an evidence-based program that county by county WIC programs decide if they're going to offer.
MEDICATIONS FOR LACTATION
In terms of medications for lactation, that's a really common question that comes up. And in general, there are very few medications that are absolutely contraindicated in breastfeeding, but they do exist.
There are some principles in general in terms of medications that would be safe for the breastfeeding dyad. In general, if it's a medication that we would prescribe to the infant, that will be safe in lactation. A fabulous resource is Thomas Hale's Medications & Mother's Milk, which is updated regularly and is a very strong evidence-based resource published that is available. You can also look at LactMed, which is produced by the National Library of Medicine.
And then finally, another resource that some are not aware of is that the Texas Tech University Health Sciences Center actually has a hotline, the Infant Risk Center. This was established by Thomas Hale, who wrote Medications & Mother's Milk.
And then finally, the Academy of Breastfeeding Medicine has about 35 different, evidence-based clinical protocols that are a really useful tool to have as well. They recently published a clinical protocol on radiology and nuclear medicine procedures in lactating women. There is one that addresses guidelines around substance use disorders in lactating women, as well as a number of other clinical protocols that address issues like supplementation mastitis, ankyloglossia, human milk storage, hypoglycemia, jaundice. That's a fantastic resource to know about.
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