Intra-oral ultrasound and vacuum studies of breastfeeding infants support the mechanobiological model of lactation-related nipple pain and damage

Analysis of ultrasound and vacuum studies corroborates the mechanobiological model of nipple pain in breastfeeding

Geddes et al 2008

In 2008 Geddes et al investigated 24 Australian infants diagnosed with ankyloglossia in the presence of breastfeeding problems, though definitions and assessment criteria for ankyloglossia were not stipulated.

Some of their mothers were found by ultrasound to have a narrowing at the base of the intra-oral nipple and breast tissue during suckling; others to have narrowing of the tip of the nipple.

These changes were not associated with difference in reports of maternal pain and resolved overall in both groups immediately post-scissors frenotomy, also associated with immediate decrease in self-reports of maternal pain.

When interpreted through the lens of the mechanobiological model of nipple pain in breastfeeding, this study shows that infants with breastfeeding problems resulting in maternal nipple pain had difficulty achieving adequate intra-oral breast tissue volumes due to conflicting intra-oral vectors of force (or breast tissue drag) and positional instability.

From the perspective of the mechanobiological model, the variable pattern of nipple and breast tissue expansion or narrowing is more likely to reflect differences in nipple and breast tissue elasticity as the intra-oral breast tissue responds to excessively high stretching mechanical loads, rather than differences in tongue movement.

Pain scores may decrease immediately after scissors frenotomy due to the infant’s sympathetic nervous system reaction and the change in fit and hold which result when a mother and baby are exposed to an environmental stressor (e.g. frenotomy), though these factors remain an omitted variable bias in existing research.1

McClellan et al 2008

In 2008, McClellan et al compared intra-oral vacuums in the babies of 30 Australian women breastfeeding successfully without nipple pain with 30 who had pain despite having received unspecified IBCLC interventions.

Infants in the pain group applied significantly higher baseline and peak vacuums, and transferred less milk despite similar sucking times. Pausing at the breast occurred for about a quarter of the feed in both groups, but infants in the pain group applied significantly higher vacuums when pausing.2

McClellan et al 2015

In 2015 McClellan et al compared 25 Australian breastfeeding women who had received IBCLC interventions without resolution of their persistent nipple pain, with 25 breastfeeding successfully without pain.3 Infants with ankyloglossia were excluded, without clarification of assessment criteria.

• Baseline vacuums were almost twice as high in the pain group, with significantly higher peak vacuums. These findings corroborated the lead author’s 2008 study, above.

• The vacuum in the pain group was stronger than the maximum comfortable pumping vacuum measured for women who were successfully breastfeeding with no pain.4

• The study also found a (statistically insignificant) trend to slower milk transfer in the pain group, consistent with the decreased milk transfer identified in women with nipple pain in 2008.

The authors conclude that nipple pain is not associated with increased milk transfer, consistent with the hypothesis that ductal compression results from conflicting intra-oral vectors of force when vacuums are excessively high.3

Pain group infants showed less expansion of the middle of the intra-oral nipple and breast tissue, and no expansion at the base, consistent with increased mechanical stretching caused by a conflicting intra-oral vector of force.

The finding of decreased depth of intra-oral space at mandible and tongue down in the pain group is also consistent with increased stretching of intra-oral breast tissue resulting from conflicting intra-oral vectors of force (or breast tissue drag), and with decreased intra-oral breast tissue volume.3

The distance between the nipple tip and the junction of the hard and soft palate (NHSPJ) was about the same between the pain and control groups. This finding however does not mean that increased breast tissue in the infant’s mouth may not be beneficial in breastfeeding, as suggested in a 2021 review,5 because the NHSPJ is just one indicator of potentially increased surface area; other indicators of decreased surface area is the decreased diameter of the intra-oral nipple and breast tissue volume, and decreased depth of intra-oral space.

In addition to primary biomechanical challenge of fit and hold, factors such as nipple and breast tissue elasticity are likely to play a role in the infant’s capacity to optimise intra-oral breast tissue volume.

Babies reflexly attempt to maximise intra-oral breast tissue volumes during breastfeeding

Interpreted from the perspective of the mechanobiological model, these ultrasound and vacuum studies of breastfeeding pairs demonstrate the effect of conflicting intra-oral vectors of force as infants reflexly attempt to optimize intra-oral breast tissue volume.

Infants generate higher baseline and peak vacuums to hold breast tissue in their mouths when the force of gravity drags the breast in a different direction, resulting in nipple pain.6

References

1. Geddes DT, Langton DB, Gollow I, et al. Frenulotomy for breastfeeding infants with ankyloglossia: effect on milk removal and sucking mechanism as imaged by ultrasound. Pediatrics 2008;122:e188-e94.
2. McClellan HI, Geddes DT, Kent JC, et al. Infants of mothers with persistent nipple pain exert strong sucking vacuums. Acta Paediatrica 2008;97(9):1205-09.
3. McClellan HL, Kent JC, Hepworth AR, et al. Persistent nipple pain in breastfeeding mothers associated with abnormal infant tongue movement. International Journal of Environmental Research and Public Health 2015;12:10833-45.
4. Kent JC, Mitoulas LR, Cregan MD, et al. Importance of vacuum for breastmilk expression. Breastfeeding Medicine 2008;3(1):9-11.
5. Geddes DT, Gridneva Z, Perrella SL, et al. 25 years of research in human lactation: from discovery to translation. Nutrients 2021;13:1307.
6. McLClellan HL, Geddes DT, Kent JC, et al. Infants of mothers with persistent nipple pain exert strong sucking vacuums. Acta Paediatrica 2008;97:1205-09.