The Breast and the Physiology of Lactation

Role of the Obstetrician in Promoting Breastfeeding

Obstetricians have many responsibilities for breastfeeding, including the following:

• Enthusiastically promoting and supporting breastfeeding, based on the published literature of its benefits advocated by the major pediatric, obstetric, and women’s health organizations. ^{, ,}

• Imparting clinical information to the lactating mother about the physiology of lactogenesis and lactation, before and after the birth.

• Developing and supporting hospital policies that facilitate breastfeeding and actively remove any barriers to it.

• Supporting community efforts to provide women with adequate information to make an informed decision about breastfeeding, including links to community breastfeeding resources.

• Providing balanced anticipatory guidance and lactation support to mothers and families regarding potential concerns during labor, delivery, the postpartum period, and breastfeeding (e.g., antenatal consultation with a breastfeeding medicine specialist or lactation specialist for anticipated needs such as suspected fetal cleft palate, multiple gestation, prematurity, and prior breast reduction surgery).

• Actively assessing women for potential breastfeeding challenges, especially those with high-risk pregnancies. Be prepared to fully evaluate and manage breastfeeding difficulties mothers encounter, personally or with the assistance of a breastfeeding medicine specialist or lactation specialist. Enabling breastfeeding in this at-risk population may ameliorate cardiometabolic disease trajectories in the mother and child dyads.

• Providing additional breastfeeding support for mothers at increased risk of low or insufficient milk production or other breastfeeding challenges.

• Proactively providing equitable lactation care addressing potential social challenges to initiating and continuing breastfeeding through the individual attention of the obstetrician and the coordinated and collaborative efforts of institutional and community-based lactation support teams.

• Fostering a general acceptance of breastfeeding by promoting a normative portrayal of breastfeeding and supporting the provision of sufficient time and facilities in the workplace.

• Performing breast examinations before and after the birth and emphasizing lactation as the primary function of the breast.

• Participating in breastfeeding education in medical and other health profession schools.

• Supporting breastfeeding within their own medical facilities by instituting the “Ten Steps to Successful Breastfeeding” as outlined by UNICEF/WHO ( Box 11.1 ).

  Box 11.1

  The Ten Steps to Successful Breastfeeding

  From UNICEF/WHO. The ten steps to successful breastfeeding. https://www.who.int/activities/promoting-baby-friendly-hospitals/ten-steps-to-successful-breastfeeding . Accessed January 28, 2021.

  Critical Management Procedures

  • 1a.

    Comply fully with the International Code of Marketing of Breast-milk Substitutes and relevant World Health Assembly resolutions.

  • 1b.

    Have a written infant feeding policy that is routinely communicated to staff and parents.

  • 1c.

    Establish ongoing monitoring and data-management systems.

  • 2.

    Ensure that staff have sufficient knowledge, competence, and skills to support breastfeeding.

  Key Clinical Practices

  • 3.

    Discuss the importance and management of breastfeeding with pregnant women and their families.

  • 4.

    Facilitate immediate and uninterrupted skin-to-skin contact and support mothers to initiate breastfeeding as soon as possible after birth.

  • 5.

    Support mothers to initiate and maintain breastfeeding and manage common difficulties.

  • 6.

    Do not provide breastfed newborns any food or fluids other than breast milk, unless medically indicated.

  • 7.

    Enable mothers and their infants to remain together and to practice rooming-in 24 hours a day.

  • 8.

    Support mothers to recognize and respond to their infants’ cues for feeding.

  • 9.

    Counsel mothers on the use and risks of feeding bottles, teats, and pacifiers.

  • 10.

    Coordinate discharge so that parents and their infants have timely access to ongoing support and care.

The mother’s plan for infant feeding should be addressed early in prenatal care, with counseling, a medical history focused on breast health and breastfeeding, and a physical examination of the breast. An outline for breastfeeding promotion in the prenatal setting is provided in the Academy of Breastfeeding Medicine’s Clinical Protocol #19. Counseling can be modeled after “The Best Start Three-Step Counseling Strategy” as suggested by Lazarov and Evans. This strategy advises beginning with open-ended questions about breastfeeding. An acknowledgment that feelings of doubt about the ability to breastfeed successfully are normal is a good place to begin. Education about breastfeeding then continues with discussion of how others have dealt with these concerns. This conversation will elucidate much about the woman’s knowledge of breastfeeding, her previous experiences with breastfeeding, and her own attitudes and those of the mother’s partner, the extended family, and other potentially supportive persons in the mother’s life. To be respectfully inclusive of all parents/families and avoid one example of discrimination and inequity as experienced by the LGBTQ+ community, affirming health care should begin with affirming names, pronouns, and consideration of the experiences and opinions of both parents. The Academy of Breastfeeding Medicine (ABM) provides some guides for providing affirming lactation care to LGBTQ+ patients and families.

To support breastfeeding optimally, the concerns of family and friends must be addressed actively to foster needed support on many levels. Misconceptions and potential barriers must be identified and reasonable solutions developed in partnership with the woman. These often include feelings of responsibility for every unexplained problem the infant displays; conflicts among a woman’s several roles as mother, sexual partner, and worker outside the home; and, most commonly, a greater time commitment and fatigue than was expected. It is important to address these and other questions repeatedly throughout pregnancy and not just in the immediate postpartum period, working closely with the infant’s pediatrician. ^, Dr. Alison Stuebe, a maternal-fetal medicine expert and a member of the Academy of Breastfeeding Medicine, utilizes open-ended questions following a format recommended by Duggan and Street that encompasses relational functions (fostering healing and validating and responding to patient emotions) of provider-patient communication and “task-driven” functions (exchanging and managing information, making treatment decisions, enabling patient self-management, and managing uncertainty) to approach maternal and familial recurring issues and concerns regarding breastfeeding. ^,

It is important to be familiar with and in communication with members of the medical team who support breastfeeding throughout the community including lactation consultants, pediatric practices, and support groups. Specific codes from the International Classification of Diseases , 10th Revision (ICD-10) commonly used for breastfeeding care and breast abnormalities are listed by ACOG to facilitate billing for the time required for informed medical care and effective communication.

Embryonic Development

The milk streak appears in the fourth week of gestation when the embryo is approximately 2.5 mm long. It becomes the milk line, or milk ridge, during the fifth week of gestation (2.5 to 5.5 mm). The mammary gland itself begins to develop at 6 weeks of embryonic life, and proliferation of the milk ducts continues throughout embryonic growth and again in pregnancy and lactation. The process of forming the nipple in the human embryo begins with a thickened, raised area of ectoderm in the region of the future gland by the fourth week of pregnancy. This thickened ectoderm becomes depressed into the underlying mesoderm and thus the surface of the mammary area soon becomes flat and finally sinks below the level of the surrounding epidermis. The mesoderm that is in contact with the ingrowth of the ectoderm is compressed, and its elements become arranged in concentric layers that at a later stage give rise to the gland’s stroma. By dividing and branching, the ingrowing mass of ectodermal cells gives rise to the future lobes and lobules, and much later to the alveoli.

By 16 weeks’ gestation in the fetus, the branching stage has produced 15 to 25 epithelial strips that represent the future secretory alveoli. By 28 weeks’ gestation, placental sex hormones enter the fetal circulation and induce canalization in the fetal mammary tissue. The lactiferous ducts and their branches are developed from outgrowth in the lumen. They open into a shallow epidermal depression known as the mammary pit. The pit becomes elevated because of mesenchymal proliferation, forming the nipple and areola. An inverted nipple is the failure of this pit to elevate. At 32 weeks’ gestation, the lumen has formed in the branching system, and by term there are 4 to 18 mammary ducts that form the fetal mammary gland. Fig. 11.2 shows the hormonal regulation of mammary development in the mouse.

The nipple, areola, and breast bud are important landmarks for the determination of gestational age in the newborn. At 40 weeks, the nipple and areola are clearly seen and the breast bud is up to 1.0 cm in diameter. In the first weeks after delivery, the breast bud is visible and palpable; however, the gland then regresses to a quiescent stage as maternal hormones in the infant diminish. After this, the gland grows only in proportion to the rest of the body until puberty.

Pubertal Development

With the onset of puberty in the female, further growth of the breast occurs, and the areolae enlarge and become more pigmented. The further development of the breast involves two distinct processes: organogenesis and milk production. The ductal and lobular growth is organogenesis, and this is initiated before and throughout puberty, resulting in the growth of breast parenchyma with its surrounding fat pad. The formation of alveolar buds begins within 1 to 2 years of the onset of menses and continues for several years, producing alveolar lobes. This menarchial stimulus begins with the extension of the ductal tree and the generation of its branching pattern. The existing ducts elongate. The ducts can develop bulbous terminal end buds that are the forerunners of alveoli. The formation of the alveolar bud begins within 1 to 2 years of the onset of menses. During this ductal growth, the alveoli enlarge and the nipple and areola become more pigmented. This growth involves an increase in connective tissue, adipose tissue, and vascular channels and is stimulated by estrogen and progesterone released by the ovary.

During the menstrual cycle, there continues to be cyclic microscopic proliferation and regression of ductal breast tissue. The breast continues to enlarge slightly with further division of the ductal system until about the age of 28 unless pregnancy intervenes.

The Mature Breast

The mature breast is located in the superficial fascia between the second and sixth intercostal cartilages and is superficial to the pectoralis muscle. It measures 10 to 12 cm in diameter. It is located horizontally from the parasternal to the midaxillary line. The central thickness of the gland is 5 to 7 cm. In the nonpregnant state, the breast weighs on average 200 g. During pregnancy, however, the size and weight increase to about 400 to 600 g, and to 600 to 800 g during lactation. Early in pregnancy there is a significant increase in ductal expansion and branching attributed to estrogen. Lobular formation increases due to prolactin, progesterone, and chorionic gonadotropin. By the third month of gestation, secretory material like colostrum is present in acini. Prolactin stimulates the secretion of colostrum in the second trimester, but production of milk prior to delivery is limited by the presence of progesterone. A projection of mammary tissue into the axilla is known as the tail of Spence and is connected to the central duct system. The breast is usually dome shaped or conic, becoming more hemispheric in the adult and pendulous in the older parous woman.

Abnormalities

In some women, mammary tissue develops at other sites in the galactic band. This is referred to as hypermastia , which is the presence of accessory mammary glands that are phylogenic remnants. These remnants may include accessory nipples or accessory gland tissue located anywhere along the milk line. From 2% to 6% of women have hypermastia. These remnants remain quiet until pregnancy, when they may respond to the hormonal milieu by enlarging and even secreting milk during lactation. If left unstimulated, they will regress after the birth. Major glandular tissue in the axilla may pose a cosmetic or management problem if the tissue enlarges significantly during pregnancy and lactation, secreting milk. It is distinct from the tail of Spence.

Other abnormalities include amastia (absence of the breast or nipple), amazia, hyperadenia, hypoplasia, polythelia, and symmastia ( Box 11.2 ). Abnormalities of the kidneys have been associated with polythelia. Other variations include hyperplasia or hypoplasia in various combinations, as listed in Box 11.3 . Gigantomastia is the excessive enlargement of the breasts in pregnancy and lactation, sometimes to life-threatening proportions. This enlargement may occur with the first or any pregnancy and may not recur. The enlargement recedes but rarely back to original size. Breastfeeding has been successful in some cases of gigantomastia with appropriate professional support. In extreme cases, gigantomastia may require heroic measures, including emergency mastectomy.

Mothers with congenital abnormalities of the breast may wish to breastfeed. Not all abnormalities or variations preclude breastfeeding, and the decision is made on a case-by-case basis.

Nipple and Areola

The skin of the breast includes the nipple and areola and the thin, flexible, elastic skin that covers the body of the breast. The nipple is a conic elevation in the center of the areola at the level of about the fourth intercostal space, just below the midline of the breast. The nipple contains smooth muscle fibers and is richly innervated with sensory and pain fibers. It has a verrucous surface and has sebaceous and apocrine sweat glands but not hair.

The areola surrounds the nipple and is also slightly pigmented and becomes deeply pigmented during pregnancy and lactation. The average diameter is 15 to 16 mm, but the range may exceed 5 cm during pregnancy. The sensory innervation is less than that of the nipple. The nipple and areola are very elastic and elongate into a teat when drawn into the mouth by the suckling infant.

The surface of the areola contains Montgomery glands, which hypertrophy during pregnancy and lactation and resemble vesicles. During lactation, they secrete a sebaceous material to lubricate the nipple and areola and protect the tissue while the infant suckles. These glands atrophy after weaning and are not visible to the naked eye except during pregnancy or lactation.

Each nipple contains 4 to 18 lactiferous ducts, of which 5 to 8 are main ducts surrounded by fibromuscular tissue. These ducts end as small orifices at the tip of the nipple from which the milk flows. The corpus mammae is an orderly conglomeration of a number of independent glands known as lobes . The morphology of the gland includes parenchyma that contains the ductular-lobular-alveolar structures. It also includes the stroma, which is composed of connective tissue, fat tissue, blood vessels, nerves, and lymphatics.

The mass of breast tissue consists of tubuloalveolar glands embedded in adipose tissue, which gives the gland its smooth, rounded contour. The mammary fat pad is essential for the proliferation and differentiation of the ductal arborization ( Fig. 11.3 ). Each lobe is separated from the others by connective tissue and opens into a duct that opens into the nipple. The extension of ducts is orderly and protected by an inhibitory zone into which other ducts cannot penetrate.

Blood is supplied to the breast from branches of the intercostal arteries and perforating branches of the internal thoracic artery. The main blood supply comes from the internal mammary artery and the lateral thoracic artery. The venous supply parallels the arterial supply.

Lymphatic drainage has been thoroughly studied by researchers of breast cancer. The main drainage is to axillary nodes and the parasternal nodes along the thoracic artery within the thorax. The lymphatics of the breast originate in lymph capillaries of the mammary connective tissue and drain through the deep substance of the breast.

The breast is innervated from the branches of the fourth, fifth, and sixth intercostal nerves. The sensory innervation of the nipple and areola is extensive and includes both autonomic and sensory nerves. The innervation of the corpus mammae is meager by comparison and is predominantly autonomic. Neither parasympathetic nor cholinergic fibers supply any part of the breast. The efferent nerves are sympathetic adrenergic. Most of the mammary nerves follow the arteries. A few fibers course along the walls of the ducts. They may be sensory fibers that sense milk pressure. No innervation has been identified to supply the myoepithelial cells. The conclusion is that secretory activities of the acinar epithelium of the ducts depend on hormonal stimulation, such as by oxytocin.

When sensory fibers are stimulated, the release of adenohypophyseal prolactin and neurohypophyseal oxytocin occurs. The areola is most sensitive to the stimulus of suckling and the nipple the least; the skin of the breast is intermediate. The large number of dermal nerve endings results in high responsiveness to suckling. Pain fibers are more numerous in the nipple, with few in the areola. All cutaneous nerves run radially toward the nipple. Breast nerves can influence the mammary blood supply and therefore also influence the transport of oxytocin and prolactin to the myoepithelial cells and the lacteal cells, respectively.