Introduction

Colostrum is the milk produced by the breast initially during the 3rd trimester of pregnancy and, subsequently, in larger volumes during the postpartum period (see Image. Breast Milk Transition). This early milk is rich in immunoglobulins and differs in caloric and protein composition from mature breast milk, which transitions into colostrum over the first 3 weeks postpartum.

Colostrum and lactation carry significant clinical implications, as early breastfeeding supports neonatal immunity, gastrointestinal maturation, and overall health outcomes. Breast surgery, including augmentation, reduction, and excision of benign or malignant tissue, can disrupt neural and ductal pathways, altering colostrum production and milk ejection, with potential consequences for the neonate’s nutrition. Familiarity with breast anatomy, surgical techniques, and lactation physiology enables clinicians to counsel patients effectively, anticipate complications, and optimize breastfeeding outcomes.

Structure and Function

The chief function of the breasts is to produce milk for infant nourishment. Colostrum provides a low-volume secretion that assists the neonate in learning to coordinate the suck, swallow, and breathing sequence during feeds. Colostrum contributes to neonatal immunity and nutrition and supports the establishment of a healthy gut microbiome, with potential long-term beneficial effects.[1]

The breasts change in size and appearance under the influence of estrogen and progesterone during pregnancy.[2] Alveolar cells initiate colostrum secretion between the 12th and 16th weeks of gestation, a process termed "lactogenesis I." Colostrum is a thick, yellowish-white fluid that may be expressed from the breast by the 3rd trimester. Milk secretion is suppressed during pregnancy due to the continued effects of estrogen and progesterone.

Colostrum, the initial milk produced by the breast during pregnancy, may be expressed during the 3rd trimester and is secreted in larger volumes postpartum. Lactogenesis II, the onset of copious milk secretion occurring 2 to 3 days after birth, produces what is termed "transitional milk." Transitional milk gradually changes from colostrum to mature milk. The volume of milk increases rapidly, immunoglobulin and protein concentrations decline, and lactose, fat, and caloric content increase. Lactogenesis III corresponds to the production of mature milk, which replaces transitional milk. Mature milk is bluish-white, less viscous, and contains approximately 20 kcal/oz, with nutrients tailored to meet the needs of the growing infant. Mature milk continues to provide immunoglobulins and additional antibacterial components.[3]

Colostrum contains higher protein concentrations and lower carbohydrate and fat content than mature breast milk.[4] Secretory immunoglobulin A in colostrum protects against infection. Colostrum also contributes to the establishment of a normal gut microbiome in the neonate, whose intestines are considered sterile at birth.

Human colostrum is the optimal nutrition for human neonates and is superior to formula or milk from other species. Nutrient proportions in human milk differ from those in other animals and are, therefore, better suited to human physiological requirements. Although infant formula is designed to replicate human milk, components such as immunoglobulins, leukocytes, antioxidants, enzymes, and hormones confer distinct advantages to colostrum and mature human milk. These benefits are particularly critical for preterm infants, who are highly susceptible to infection and derive substantial protection and developmental support from colostrum and human milk.[5][6][7]

Embryology

Female breast development in the fetus begins during the 4th week of gestation. By 16 weeks, smooth muscle has formed in the nipple and areola, and epithelial cells differentiate into mammary buds. These buds subsequently branch into alveoli and ducts, establishing the mammary system. Mammary gland development continues throughout childhood and accelerates during puberty, with rapid proliferation of ducts and alveoli. Hormones associated with each menstrual cycle further stimulate the proliferation and growth of mammary tissue.[8]

Blood Supply and Lymphatics

The breast is highly vascularized, primarily supplied by the internal mammary and lateral thoracic arteries.[9] Numerous lymphatic vessels are present within the breast and axilla. These lymphatic vessels follow the lactiferous ducts and converge near the nipple. Lymphatic fluid may accumulate during the engorgement phase of breastfeeding, typically occurring 3 to 5 days postpartum, contributing to visible breast distention. Milk components are synthesized within the alveoli, including protein, fat, and carbohydrates, or are derived from maternal plasma, such as vitamins and minerals.

Nerves

The posterior pituitary secretes oxytocin in response to infant suckling at the breast.[10] The nipple and areola contain a high density of sensory nerve endings. Oxytocin release initiates the milk ejection reflex (MER), also referred to as the "letdown reflex."[11] Contraction of myoepithelial cells surrounding the alveoli propels milk through the lactiferous ducts and out of the nipples. The mother may experience a tingling sensation during this process. Infant suckling also stimulates prolactin secretion. Prolactin levels increase during pregnancy, decline shortly before birth, and rise again postpartum. Prolactin concentrations approximately double in response to infant suckling.

Physiologic Variants

Factors influencing prolactin release and subsequent milk production include breast stimulation, sleep, stress, and pregnancy. Medications that stimulate prolactin secretion include neuroleptic agents, thyroid-releasing hormone, metoclopramide, estrogens, phenothiazines, norepinephrine, histamine, and acetylcholine. Medications that suppress prolactin include levodopa, ergot derivatives, clomiphene citrate, pyridoxine, monoamine oxidase inhibitors, and prostaglandins E and F.[12][13][14]

Multiple physiologic variables, both maternal and neonatal, can affect breastfeeding and, consequently, colostrum intake. Maternal factors include nipple size and shape, breast development during puberty and pregnancy, mammoplasty (reduction or augmentation), other breast surgery, fibrocystic changes, breast cancer, obesity, and concurrent medical conditions. Neonatal factors that may influence breastfeeding include gestational age at birth, ankyloglossia, cleft lip or palate, and other physical malformations; infections; oral-motor dysfunction; and conditions such as congenital heart disease, cystic fibrosis, inborn errors of metabolism, intestinal malabsorption syndromes, neurological disorders, renal pathologies, and thyroid disease.

Nipple size and shape are among the most common factors influencing the initial days of breastfeeding when colostrum is received. A more erect nipple facilitates neonatal latching and effective suckling. Flat or inverted nipples may impede the mother and neonate from establishing successful breastfeeding. Nipple shields may be employed, although their effectiveness is limited.

Neonatal wakefulness and the ability to suck are additional critical factors. Optimal promotion of breastfeeding involves providing skin-to-skin contact between the mother and the infant within 5 minutes of birth for a minimum of 1 hour. This contact supports physiological adaptation to extrauterine life and enables the neonate to locate the nipple through olfactory and tactile cues. Skin-to-skin contact also contributes to the establishment of normal cutaneous flora in the neonate, thereby protecting against pathogenic bacteria. Successful breastfeeding within the 1st hour postpartum establishes a foundation for improved breastfeeding outcomes in subsequent days.

Surgical Considerations

The role of the interprofessional team in the evaluation and management of women is critical. Breast surgical procedures can influence milk production and ejection. Key factors include the type of surgery performed, disruption of neural or ductal pathways, and the volume of breast tissue removed.

Breast augmentation typically does not impede full breastfeeding, whereas breast reduction surgery frequently compromises the ability to breastfeed. Certain breast reduction procedures involve complete removal and subsequent reattachment of the nipple after excision of excess tissue, which disrupts neural and ductal pathways. The pedicle technique preserves nipple attachment while removing surrounding tissue, increasing the likelihood of maintaining milk production and ejection. Surgical intervention for benign tumors or malignancy can similarly affect the breast's capacity to produce milk.[15]

Clinical Significance

The interprofessional team should consider the patient’s age and future reproductive or lactation plans whenever breast surgery is contemplated. Patients should receive counseling regarding the risks and benefits of surgical and nonsurgical breast interventions and their potential impact on future breastfeeding, enabling informed decision-making.[16] The healthcare team should also evaluate the effects of medications on colostrum, breastfeeding, and neonatal suckling. Patients require thorough counseling on indications, interactions, and potential adverse effects for both the patient and the neonate.[17][18] The interprofessional team should provide education on the significance of colostrum for neonatal health and support early breastfeeding experiences to optimize breastfeeding outcomes and promote neonatal well-being.

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Disclosure: Felix Jozsa declares no relevant financial relationships with ineligible companies.

Disclosure: Jennifer Thistle declares no relevant financial relationships with ineligible companies.