A constitutive model description of the in vivo material properties of lower birth canal tissue during the first stage of labor

Paige V. Tracy, Alan S. Wineman, Francisco J. Orejuela, Susan M. Ramin, John O.L. DeLancey, James A. Ashton-Miller

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


Remarkable changes must occur in the pelvic floor muscles and tissues comprising the birth canal to allow vaginal delivery. Despite these preparatory adaptations, approximately 13% of women who deliver vaginally for the first time (nulliparas) sustain tears near the origin of the pubovisceral muscle (PVM) which can result in pelvic organ prolapse later in life. To investigate why these tears occur, it is necessary to quantify the viscoelastic behavior of the term pregnant human birth canal. The goal of this study was to quantify the in vivo material properties of the human birth canal, in situ, during the first stage of labor and compare them to published animal data. The results show that pregnant human, ovine and squirrel monkey birth canal tissue can be characterized by the same set of constitutive relations; the interspecies differences were primarily explained by the long time constant, τ 2 , with its values of 555 s, 1110 s, and 2777 s, respectively. Quantification of these viscoelastic properties should allow for improved accuracy of computer models aimed at understanding birth-related injuries.

Original languageEnglish (US)
Pages (from-to)213-218
Number of pages6
JournalJournal of the Mechanical Behavior of Biomedical Materials
StatePublished - Mar 2018

Bibliographical note

Funding Information:
We thank Mr. Mark Juravic of Materna Medical, Inc., for contributing the de-identified human birth canal force-displacement data free of charge under a three-way data sharing agreement between his company, Baylor College of Medicine and the University of Michigan. We thank Drs. Susan Ramin and Francisco Orejuela at Baylor College of Medicine for conducting the clinical trial, funded by Materna, that gave rise to the data we were able to use. We would also like to thank Sharon Edwards and the team at Prince Henry's Institute and the Monash Institute of Medical Research in Melbourne, Australia for their generosity in sharing their ovine specimen data. We gratefully acknowledge financial support from the Public Health Service and the Office for Research on Women and Gender grant P50 HD044406-07 for Project 1 entitled “Pelvic Floor Biomechanics and Birth-Related Injury”. No financial support was provided by Materna Medical, Inc.

Publisher Copyright:
© 2017 Elsevier Ltd


  • Birth
  • Constitutive model
  • Levator ani
  • Quasilinear viscoelasticity


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