Foundations of Breastfeeding: Milk Flow and Infant Oral Anatomy

by Christine Staricka, BS, IBCLC, CCE

The velocity of milk flow is not a specifically predictable factor in breastfeeding, and it cannot be replicated by observing milk expression manually or by using an electric breastpump.  The velocity of milk flow is relevant ONLY relative to the baby's ability to manage it; therefore, to calculate or label it would not predict a baby's capacity to feed efficiently.  It becomes relevant when it is observed that a baby is not managing milk flow comfortably or efficiently.  However, understanding how milk flows from the breast is imperative to comprehending how infant oral anatomical variations may affect efficiency of breastfeeding.  

 

The velocity of milk flow at each feeding is determined by multiple factors:

-time since birth of the baby

-fullness of the breast

-time since last emptying of the breast

-intrinsic maternal factors affecting nerve response and reflex, as well as maternal milk storage capacity

 

In addition, the velocity changes throughout the feeding.

In the immediate postpartum period, milk flow is slow and milk is extracted in small volumes.  The newborn suckles at the breast to obtain its milk. Long suckling sessions maintain the newborn's level of hydration and stimulate digestion and the passage of meconium.  Because nutrients transferred to the newborn through the umbilical cord until the moment it was cut, the newborn does not require large volumes of milk.  When the newborn has completed a suckling session, hunger cues cease and the infant rests.

During this time, the newborn completes the process of coordinating the suck/swallow/breathe pattern of feeding which was begun months earlier inutero.    At an average time of 30-40 hours postpartum, the flow of milk begins to steadily increase with the onset of copious milk production.  By this time the newborn requires additional hydration, so the milk transitions to contain more water than the earlier milk. As the milk begins to flow faster, the newborn proceeds with the suck/swallow/breathe pattern and uses longer pauses for recovery between bursts of 10-12 sucks.  When the newborn begins to feel satiated, hunger cues cease and satiation cues begin to appear.  

As the production of milk increases throughout the breastfeeding establishment period, the flow of milk can be quite variable depending upon the mother's capacity to store milk between feedings.  The infant stimulates the release of milk by suckling; this release is triggered by a combination of mechanical and hormonal stimulation of the breast.  After an initial spray, milk does not continue to flow unabated; rather, the infant creates a pattern of rising and falling intraoral pressure to continue extracting milk.  When the milk slows, if the infant wishes to continue the feeding, he returns to a faster rhythm of sucking to stimulate another milk ejection reflex.  Therefore, there are 2 distinct types of milk flow during breastfeeding: the milk ejection reflex and the controlled milk flow phase.  As the milk flow slows after a period of rhythmic pressure alteration, if the infant requires more milk, he increases the speed of pressure alteration to elicit a milk ejection reflex, then decreases the speed after the MER slows. Milk flows differently during each phase, and the infant cycles through the phases until hormonal signals of fullness are internally released, and he then usually detaches from the breast. 

To conduct this process of feeding, the infant creates an intricate chamber in the oral space to accomodate and manipulate the nipple/areolar complex of his mother.  He then enacts complex movements of his oral anatomy to extract, transport, and swallow milk.  During the process of attachment to the breast at the nipple/areolar complex, the infant extends his tongue over his lower gumline while widely gaping at the jaw.  Both of his lips flange outward as he attaches, and complete attachment is achieved when his mouth seals completely, partially or fully covering the nipple/areolar complex (depending on its unique size and shape, which varies from breast to breast even in the same woman.)  Once attached, the infant begins to suck by repeatedly lowering and then raising the posterior portion of the tongue.  This speed of this vertical motion dictates the type of milk release: rapid motion  stimulates the milk ejection reflex, while slower motion enables controlled milk release.  

Simultaneously, other anatomical structures are at work maintaining the stability of the attachment and performing the milk transport activities.  The inner portion of the infant's cheeks form the walls of the cavity, while the palate forms the roof and the tongue is the floor.  The anterior portion of the tongue rests unmoving between the lower gumline and the mother's nipple.  The side edges of the tongue roll slightly vertically toward the palate to create a channel for the milk to flow backward toward the throat, and the swallow reflex is triggered as necessary.  The infant's flanged lips complete the sealed environment in order to contain the alterations of vacuum and pressure inside the cavity.

The pliability of the breast tissue and the elasticity of the nipple also play a role in determining the quality of the infant's attachment to the breast and the efficiency of breastfeeding.  These factors are also highly variable and dependent upon similar triggers to the rate of milk flow.  A healthy infant who has uninterrupted access to the breast from the time of birth helps to improve both pliability of breast tissue through frequent emptying of the breast as well as nipple elasticity through repeated stretching and elongating of the ligaments within the nipple and areola.  

Variations

Variations of normal infant oral anatomy include improperly formed structures, such as clefts of the lip or palate, as well as the presence of restrictive tissues which bind structures in ways that prevent normal movement and function.  Restrictive tissues, also known as tethered oral tissues, can affect the normal process of breastfeeding and cause a multitude of symptoms in mother and baby. Visual assessment of the structures provides a partial window into the capacity for normal function, but the functional capacity of the structures can only be evaluated by observing the function itself.  

In evaluating for appropriate breastfeeding function, it is critical to evaluate all elements of the system: mother,  baby, and breastfeeding.  If any one element is presenting abnormal outcomes, all element of the system must be addressed.  For example, if breastfeeding is causing nipple trauma for the mother, the IBCLC evaluates each element of the system in order to treat the symptom as well as to prevent further complications in other elements such as milk stasis or poor milk transfer.  Looking only at the way the baby latches to the breast, or simply providing instruction to the mother on appropriate latch technique is a function of a provider of basic breastfeeding support such as a La Leche League Leader or a lactation educator/counselor.  The Scope of Practice for the IBCLC requires that the IBCLC evaluate and address all elements of the dyad for normal function and normal outcomes.  

Observation of movements during feeding provide key pieces of information about function.  The overall rhythm and "smoothness" of breastfeeding should be clear and obvious.  If stuttering or choppy movements are observed during suckling, if the infant is unable to initiate and maintain a pattern of suckling, or if the infant repeatedly detaches and re-attaches to the breast, these all indicate dysfunction, regardless of the infant's age.  The emergence of the mother's nipple from the infant's mouth with a pinched or compressed appearance indicates dysfunction.  A stressed appearance in the infant during feeding, usually indicated by furrowed or raised brows along with splayed fingers and toes, indicates infant dysfunction.  A stressed appearance in the mother during feeding, indicated by furrowed or raised brows, hunching forward of the shoulders, grimacing, or verbal expressions, can indicate maternal pain or dysfunction and must be addressed as equally significant as infant indicators.  

Visual evaluation of the infant oral anatomy can provide important information regarding function; it is important to observe as many movements as possible.  

-During crying - observe both anterior and posterior portions of tongue, observe for symmetry of tongue lift

-During yawning - observe both anterior and posterior portions of tongue, observe angle of jaw opening and ability to gape widely, observe for mobility of upper and lower lip

-While performing Murphy maneuver

-When infant's mouth is at rest - observe for symmetry of external oral and facial structures, observe for mouth movements away from feeding time such as intermittent jaw clenching, tongue sucking, generally tight movements of mouth during rest time

Visual assessment of the overall structure of the infant's mouth and the movement of its individual parts can enhance understanding of where dysfunction is occurring.  For example, the observation of a blister in the center of baby's upper lip indicates that the pressures being created in the oral cavity are being diverted toward the lips to maintain the seal, rather than occurring and remaining at the posterior tongue for milk extraction.  Similarly, the observation that during elevation an infant's tongue creates a "bowl" with a humped posterior indicates that the infant may be unable to properly lift the sides of the tongue to manage the bolus of milk and transport it to the soft palate to trigger swallowing.  An infant with low muscle tone in the cheeks or minimal fat pads on the cheeks may have difficulty creating a properly sealed oral cavity because the cheek walls do not reach the tongue and so do not become the "walls" of the cavity.  

Symptoms

Mothers reporting the following symptoms or situations should be thoroughly evaluated by an IBCLC:

-difficulty latching baby at birth and during first 48 hours of life even when infant is properly positioned for self-latching (failure of a properly positioned newborn to self-attach to the breast indicates an improperly functioning reflex or an oral dysfunction)

-mother describing baby as unable to gape widely for latch (infant's lower jaw should drop noticeably during yawning and when approaching the breast for attachment; inability to gape widely indicates an oral dysfunction)

-nipple pain which persists throughout feedings (normal oral movement during breastfeeding does not create friction or compression of maternal structures; initial tenderness at time of attachment due to stretching of ligaments generally resolves within first 30 seconds, so pain which persists past that time indicates oral dysfunction) 

-nipple trauma (normal oral movement during breastfeeding does not create friction or compression and thus does not create trauma or breakdown of skin on nipple)

-consistently poor breast emptying by infant, necessitating mechanical or manual milk expression to facilitate maternal comfort or to protect or increase milk supply (normally functioning, healthy, breastfed infants regulate milk supply without other interference)

-infection of nipple or breast diagnosed by a physician, whether or not prescription medications are indicated or prescribed; or suspected infection of nipple or breast  (nipple trauma or breakdown facilitates uptake of infectious microbes by the breast)

-poor milk transfer by infant, indicated by test weights and visual observation of a breastfeeding session (normally functioning, healthy breastfed infants transfer volumes of milk sufficient to meet their needs when permitted access to the breast on demand)

-poor weight gain in infant, indicated by weight loss after the first 10-14 days of life or failure to gain weight over time (normally functioning, healthy, breastfed infants typically increase weight, length, and head circumference on an upward trend over time)

-jaundice requiring treatment by phototherapy or additional feeding (physiologic jaundice is monitored and exclusive breastfeeding is continued, but pathologic jaundice may indicate other breastfeeding dysfunction)

-blisters on infant's lips which are pronounced after feedings (normally flanging lips have elasticity and seal to the breast without the infant exerting excessive pressures to maintain the seal)

-inability of infant to maintain latch during a feeding; infant breaks seal repeatedly and requires re-latching (infants latched well pause for recovery between bursts of suckling but do not routinely detach from the breast until satiated)

-choking, gasping, gulping, sputtering during breastfeeding (normally functioning, healthy, breastfed infants control milk flow through rhythmic alterations of suckling)

-clicking sound during breastfeeding (a properly latched infant does not take in air when sealed to the breast)

-maternal description of breastfeeding including terms such as biting, chewing, gumming, clenching (normal breastfeeding is described by mothers as tugging, pulling, or sucking)

-low frequency of voids in infant (normally functioning, healthy, breastfed infants require no additional fluids for hydration during the first 6 months of life)

-poor stool output in infant, defined as failure to stool daily (normally functioning, healthy, breastfed infants with a healthy microbiome typically stool at least daily)

-infant regurgitating frequently; suspected or diagnosed acid reflux condition (normally functioning, healthy, breastfed infants may spit up occasionally but not excessively, generally if they have taken in air during a period of crying)

-maternal description of infant "breastfeeding constantly" with only brief intervals between feeds inclusive of entire 24-hour periods (normally functioning, healthy, breastfed infants breastfeed effectively to clear signs of satiation, utilize intervals between feedings for quiet alert states and cycle between light and deep sleep periods easily) 

**Normally functioning, healthy breastfed infant = exclusively breastfed (at the breast) infant permitted to access the breast and to sleep and wake entirely on demand**

**  While not all these symptoms indicate a breastfeeding problem related to tethered oral tissues, all of them indicate breastfeeding symptoms indicating a need for thorough IBCLC care.  **

Artificial Teats: Nipple Shields, Bottles, Pacifiers

By altering the shape, texture, and pliability of the nipple/areolar complex, a nipple shield creates a different structure to which the infant attaches. This artificial nipple can mask or bypass infant oral anatomy variations.  Some, but not all, infants are able to transfer milk through a shield.  The barrier of a shield between the infant’s mouth and the mother’s breast reduces necessary hormonal signals and microbial transfer between the two, altering the shared environment of the breast as communication between mother and baby.  

An artificial nipple used on a bottle can similarly bypass infant oral anatomy variations.  Frequently, the length of the artificial nipple, as well as the firm structure can gently force the tongue into creating the channel necessary for managing the flow of milk from the bottle.  Milk flow from a bottle varies widely, dependent upon the size of the nipple opening and the angle at which liquid is being forced into the nipple by the feeder.  The infant can control this flow by biting or compressing the nipple rather than altering pressures as they do while breastfeeding.  

The use of a pacifier can mask symptoms and bypass infant signals.  In the presence of infant oral anatomy variations, bypassing these signals delays appropriate return to normal breastfeeding.