The Watson Genna et al 2021 study of the biomechanics of infant suck in breastfeeding has serious limitations
This series of NDC (Neuroprotective Developmental Care) analyses of new research in the fields of breastfeeding, lactation, and infant care acknowledge the tremendous amount of work that goes into each new study and it's publication, celebrating the passion authors have for advancing knowledge in the clinical care of parents with infants. The series also claims the importance of respectful dissent and debate, which is fundamental to the advancement of science and the care of families. Our small team at The NDC Institute: Home of the Possums Programs hope that researchers whose work Pam analyses and critiques accept the sincere respect from which we offer differing perspectives, as together we serve the shared value of contributing to better outcomes for families.
There are multiple methodological weaknesses in Genna et al's 2021 study
Cathy Watson Genna et al’s 2021 study, published with David Elad’s team, is now often used in discussions of the biomechanics of infant suck and swallow. But there are multiple methodological weaknesses in this single study; nor does it tell us anything new.
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There's little reason to believe that creating submental ultrasound videos and analysing the recordings using computational techniques is any more objective or reliable than creating submental ultrasound videos and analysing them using the standard measurement of recorded videos by an observer, such as has been implemented in the Geddes Hartmann Human Lactation Research Group’s extensive ultrasound studies analysing infant suck in breastfeeding. Adding in a layer of computerized data analysis is not necessarily more objective or more accurate – this has not been established.
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Importantly, Genna et al's study lacks information about how the four infants’ medical conditions of airways instability, tongue-tie, and dysphagia were diagnosed. It’s true that the final, fifth subject, an adult swallowing water, was found to have a peristaltic-like movement from the anterior tongue through to the posterior tongue, which is to be expected and is very different to the biomechanics of an infant suckling at the breast.
Genna et al 2021 lacks clarity about the posterior tongue and doesn't consider multiple confounding factors
There is often confusion about the differences between the anterior, mid, and posterior tongue, which might be a problem in the way Genna et al 2021 is interpreted by readers.
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The posterior tongue, which is generally agreed to have movement akin to peristalsis, is not visible on clinical oral inspection and is not connected anatomically to the floor of mouth fascia or frenulum.
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The visible part of the tongue (anterior and mid) move enbloc with the jaw drop, as one.
In this respect Genna et al doesn’t tell us anything new. The findings of changes in posterior tongue movements after frenotomy could be explained by other factors, such as an infant’s upregulated sympathetic nervous system post-surgery, though these are not considered.
An MRI study (Mills et al 2020) of 8 shows that most successfully breastfeeding infants don’t flange or evert their lips against the breast, yet Genna et al attribute changes in the posterior tongue movements to the labial frenotomy, to which the improved capacity to latch is also attributed. There are multiple other studies demonstrating that labial frenotomy doesn't improve breastfeeding outcomes. There is no place for labial frenotomy in the management of breastfeeding problems. Fit and hold and its impact on tongue shape and movement remains an omitted variable bias in this Watson Genna et al 2021 in this study. Any change in the posterior tongue movement noted by this team post-labial-frenotomy is likely to have other explanations, which are not considered.
For a detailed explanation of the biomechanics of infant suck and swallow please read the open access research paper here or watch the animation here.
Has a peer review process occurred prior to publication of Genna et al 2021?
According to the notations on this team's publication, there was an eight day turnaround from submission of this study to its publication. Unless there is a mistake in the publication of dates, such rapid turnaround is extremely unusual, and raises serious questions about rigor of - or the existence of any meaningful - peer review. As a matter of course, researchers wait months for their manuscript to
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Pass initial editor's approval (many submissions are rejected initially - that is, not accepted for the review process in that journal)
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Be sent out to selected reviewers, who either consent to review or reject the request. Just finding reviewers can take the editor weeks.
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Be reviewed and have that review usually by two reviewers, at least, returned to the editor
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Have the article accepted without change (very unlikely), rejected at that point in time, or invited for further re-write in response to reviewers critique (most common option)
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Move through the process in which the editor and often the reviewers again review the revised draft. This can sometimes happens twice or more, iteratively
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Wait weeks or even much longer, once the author is notified that the publication will proceed, for the article to appear in the next online edition of the journal.
The time that is invested in peer review, and responses which are approved by the reviewers, is a vital part of establishing the credibility of any research publication.
Recommended resources
How babies breastfeed: the biomechanics of infant suck (short animation)
How babies breastfeed: the biomechanics of infant suck - video and animation
Ultrasound and vacuum studies elucidate the biomechanics of the infant suck cycle in breastfeeding
Selected references
Douglas PS, Perrella SL, Geddes DT. A brief gestalt intervention changes ultrasound measures of tongue movement during breastfeeding: case series. BMC Pregnancy and Childbirth. 2022;22(1):94. DOI: 10.1186/s12884-12021-04363-12887.
Genna CW, Saperstein Y, Siegel SA, Laine AF, Elad D. Quantitative imaging of tongue kinematics during infant feeding and adult swallowing reveals highly conserved patterns. Physiological Reports. 2021;9:e14685.
Mills N, Lydon A-M, Davies-Payne D, Keesing M, Mirjalili SA, Geddes DT. Imaging the breastfeeding swallow: pilot study utilizing real-time MRI. Laryngoscope Investigative Otolaryngology. 2020;5:572-579.