Understanding how a baby extracts milk from the breast is essential to practising sound, effective breastfeeding management. This is necessary to optimise milk transfer from mother to baby, in turn, allowing one to maximise the transfer of calorie rich nutrients (predominantly breast milk fat).
For several centuries, received wisdom was that babies extract milk from the breast by a combination of baseline suction, compression and relaxation of the baby’s jaws against the breast, and rhythmical application of waves of pressure applied to the underside of the breast/nipple held within the baby’s mouth by the tongue. Based on this premise the core principles of WHO/UNICEF training were established, focusing on optimising the ‘positioning’ and ‘attachment’ of the baby at the breast, in order to maximise the effectiveness of milk transfer.
In the past decade, this received wisdom was challenged by the use both of modern ultrasound equipment and engineering-based modelling of breast anatomy (specifically the milk duct system) and the baby’s sucking action. A key novel claim was made that the baby can generate localised, ‘added’ suction with its tongue to enhance milk transfer; this has since been confirmed, although the evidence is that this novel mechanism remains secondary to the core process of peristaltic expression by the tongue. In contrast, the engineering-based studies have proved contradictory, providing new insights yet posing fresh challenges. To date, however, they have not produced a definitive view, nor have they altered the core underpinnings of best breastfeeding practice and management.
In the field of Medicine, it is recognised that the validity of Randomised Controlled Trials (RCTs) should be evaluated by a set of quality control standards, and the Critical Appraisal Skills (CASP) framework is a way of achieving this. No such quality standards or guidelines exist for evaluating engineering-based models of a physiological process. So, in order to address the veracity of the conclusions drawn, I have sought to evaluate the assumptions made in these models; whether or not they are valid; and whether specific elements are missing from current models which might affect their outcome.
Certain physical assumptions, made during the modelling process, are known to be incorrect, but have been made in order to simplify the modelling process (i.e. the ducts are rigid). Further ways in which the modelling process departs from known physiology include the view that negative suction pressure is the exclusive force in these models, without any contribution being made by the progressive peristaltic pressure exerted by the baby’s tongue. The models also make the core assumption that the milk duct system remains patent throughout a feed, thereby ignoring the occlusive impact of the baby’s jaw closure with each suck. The inclusion of any one of these natural processes would radically alter the conclusions from modelling, thereby disproving the claim that ‘suction alone can explain milk extraction’ while giving greater credence to the suggestion that ‘suction alone may not fully explain milk extraction’.
One feature consistently missing from such analyses is the clinical implications arising from them, and what they add to our understanding in terms of how to help mothers and babies breastfeed more effectively. To this end, the pivotal role played by peristaltic tongue movements, essential to effective breastfeeding, will be identified and elaborated, so providing evidence as to why the core management principles of ‘Positioning’ and ‘Attachment’ remain central to breastfeeding success.
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