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Research Papers

A Geometric Capacity–Demand Analysis of Maternal Levator Muscle Stretch Required for Vaginal Delivery

[+] Author and Article Information
Paige V. Tracy

Department of Biomedical Engineering,
University of Michigan,
Ann Arbor, MI 48109
e-mail: voigtpai@umich.edu

John O. DeLancey

Department of Obstetrics and Gynecology,
University of Michigan,
Ann Arbor, MI 48109

James A. Ashton-Miller

Department of Mechanical Engineering,
University of Michigan,
Ann Arbor, MI 48109

1Corresponding author.

Manuscript received September 1, 2015; final manuscript received December 11, 2015; published online January 27, 2016. Editor: Beth A. Winkelstein.

J Biomech Eng 138(2), 021001 (Jan 27, 2016) (12 pages) Paper No: BIO-15-1434; doi: 10.1115/1.4032424 History: Received September 01, 2015; Revised December 11, 2015

Because levator ani (LA) muscle injuries occur in approximately 13% of all vaginal births, insights are needed to better prevent them. In Part I of this paper, we conducted an analysis of the bony and soft tissue factors contributing to the geometric “capacity” of the maternal pelvis and pelvic floor to deliver a fetal head without incurring stretch injury of the maternal soft tissue. In Part II, we quantified the range in demand, represented by the variation in fetal head size and shape, placed on the maternal pelvic floor. In Part III, we analyzed the capacity-to-demand geometric ratio, g, in order to determine whether a mother can deliver a head of given size without stretch injury. The results of a Part I sensitivity analysis showed that initial soft tissue loop length (SL) had the greatest effect on maternal capacity, followed by the length of the soft tissue loop above the inferior pubic rami at ultimate crowning, then subpubic arch angle (SPAA) and head size, and finally the levator origin separation distance. We found the more caudal origin of the puborectal portion of the levator muscle helps to protect it from the stretch injuries commonly observed in the pubovisceral portion. Part II fetal head molding index (MI) and fetal head size revealed fetal head circumference values ranging from 253 to 351 mm, which would increase up to 11 mm upon face presentation. The Part III capacity-demand analysis of g revealed that, based on geometry alone, the 10th percentile maternal capacity predicted injury for all head sizes, the 25th percentile maternal capacity could deliver half of all head sizes, while the 50th percentile maternal capacity could deliver a head of any size without injury. If ultrasound imaging could be operationalized to make measurements of ratio g, it might be used to usefully inform women on their level of risk for levator injury during vaginal birth.

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References

Lien, K.-C. , DeLancey, J. O. L. , and Ashton-Miller, J. A. , 2009, “ Biomechanical Analyses of the Efficacy of Patterns of Maternal Effort on Second-Stage Progress,” Obstet. Gynecol., 113(4), pp. 873–880. [CrossRef] [PubMed]
Silva, M. E. T. , Oliveira, D. A. , Roza, T. H. , Brandao, S. , Parente, M. P. L. , Mascarenhas, T. , and Natal Jorge, R. M. , 2015, “ Study on the Influence of the Fetus Head Molding on the Biomechanical Behavior of the Pelvic Floor Muscles, During Vaginal Delivery,” J. Biomech., 48(9), pp. 1600–1605. [CrossRef] [PubMed]
Yan, X. , Kruger, J. A. , Nielsen, P. M. , and Nash, M. P. , 2015, “ Effects of Fetal Head Shape Variation on the Second Stage of Labour,” J. Biomech., 48(9), pp. 1593–1599. [CrossRef] [PubMed]
Shek, K. , and Dietz, H. , 2010, “ Intrapartum Risk Factors for Levator Trauma,” BJOGP, 117(12), pp. 1485–1492. [CrossRef]
Margulies, R. , Huebner, M. , and DeLancey, J. , 2007, “ Origin and Insertion Points Involved in Levator Ani Muscle Defects,” Am. J. Obstet. Gynecol., 196(3), pp. 251–255. [CrossRef] [PubMed]
Mant, J. , Painter, R. , and Vessey, M. , 1997, “ Epidemiology of Genital Prolapse: Observations From the Oxford Planning Association Study,” Br. J. Obstet. Gynaecol., 104(5), pp. 579–585. [CrossRef] [PubMed]
Ashton-Miller, J. A. , and DeLancey, J. O. , 2009, “ On the Biomechanics of Vaginal Birth and Common Sequelae,” Annu. Rev. Biomed. Eng., 11(1), pp. 163–176. [CrossRef] [PubMed]
Betschart, C. , Kim, J. , Miller, J. M. , Ashton-Miller, J. A. , and DeLancey, J. O. L. , 2014, “ Comparison of Muscle Fiber Directions Between Different Levator Ani Muscle Subdivisions: In Vivo MRI Measurements in Women,” Int. Urogynecol. J., 25(9), pp. 1263–1268. [CrossRef] [PubMed]
Kearney, R. , Sawhney, R. , and DeLancey, J. , 2004, “ Levator Ani Muscle Anatomy Evaluated by Origin-Insertion Pairs,” Am. Coll. Obstet. Gynecol., 104(1), pp. 168–173. [CrossRef]
Lien, K. , Mooney, B. , DeLancey, J. , and Ashton-Miller, J. , 2004, “ Levator Ani Muscle Stretch Induced by Simulated Vaginal Birth,” Obstet. Gynecol., 103(1), pp. 31–40. [CrossRef] [PubMed]
Miller, J. M. , Brandon, C. , Jacobson, J. A. , Low, L. K. , Zielinski, R. , Ashton-Miller, J. , and Delancey, J. O. , 2010, “ MRI Findings in Patients Considered High Risk for Pelvic Floor Injury Studied Serially After Vaginal Childbirth,” Am. J. Roentgenol., 195(3), pp. 786–791. [CrossRef]
Brandon, C. , Jacobson, J. , Low, L. , Park, L. , DeLancey, J. O. , and Miller, J. , 2012, “ Pubic Bone Injuries in Primiparous Women: Magnetic Resonance Imaging in Detection and Differential Diagonosis of Structural Injury,” Ultrasound Obstet. Gynecol., 39(4), pp. 444–451. [CrossRef] [PubMed]
Luo, J. , Ashton-Miller, J. A. , and DeLancey, J. O. L. , 2011, “ A Model Patient: Female Pelvic Anatomy can be Viewed in Diverse 3-Dimensional Images With a New Interactive Tool,” Am. J. Obstet. Gynecol., 205(4), pp. 391.e1–391.e2. [CrossRef]
Alperin, M. , Lawley, D. M. , Esparza, M. C. , and Lieber, R. L. , 2015, “ Pregnancy-Induced Adaptations in the Intrinsic Structure of Rat Pelvic Floor Muscles,” Am. J. Obstet. Gynecol., 213(2), pp. 191–197. [CrossRef] [PubMed]
Brooks, S. V. , Zerba, E. , and Faulkner, J. A. , 1995, “ Injury to Muscle Fibers After Single Stretches of Passive and Maximally Stimulated Muscles in Mice,” J. Physiol., 488(2), pp. 459–469. [CrossRef] [PubMed]
Kirilova, M. , Stoytchev, S. , Pashkouleva, D. , and Kavardzhikov, V. , 2011, “ Experimental Study of the Mechanical Properties of Human Abdominal Fascia,” Med. Eng. Phys., 33(1), pp. 1–6. [CrossRef] [PubMed]
Kim, J. , Ramanah, R. , DeLancey, J. , and Ashton-Miller, J. A. , 2011, “ On the Anatomy and Histology of the Pubovisceral Muscle Enthesis in Women,” Neurourol. Urodyn., 30(7), pp. 1366–1370. [PubMed]
Kim, J. , Betschart, C. , Ramanah, R. , Ashton-Miller, J. , and DeLancey, J. , 2015, “ Anatomy of the Pubovisceral Muscle Origin: Macroscopic and Microscopic Findings Within the Injury Zone,” Neurourol. Urodyn., 34(8), pp. 774–780. [CrossRef] [PubMed]
Larson, K. , Luo, J. , Yousuf, A. , Ashton-Miller, J. , and DeLancey, J. , 2012, “ Measurement of the 3D Geometry of the Fascial Arches in Women With a Unilateral Levator Defect and Architectural Distortion,” Int. Urogynecol. J., 23(1), pp. 57–63. [CrossRef] [PubMed]
Handa, V. L. , Lockhart, M. E. , Fielding, J. R. , Bradley, C. S. , Brubaker, L. , Cundiff, G. W. , Ye, W. , and Richter, H. E. , 2008, “ Racial Differences in Pelvic Anatomy by Magnetic Resonance Imaging,” Obstet. Gynecol., 111(4), pp. 914–920. [CrossRef] [PubMed]
Albrich, S. , Shek, K. , Krahn, U. , and Dietz, H. , 2015, “ Measurement of the Subpubic Arch Angle by 3D Translabial Ultrasound and Its Impact on Vaginal Delivery,” Ultrasound Obstet. Gynecol., 46(4), pp. 496–500. [CrossRef] [PubMed]
Centers for Disease Control and Prevention, 2010, “ Data Table for Boys Weight-for-Length and Head Circumference-for-Age Charts,” Last accessed June 18, 2015, http://www.cdc.gov/growthcharts/who/boys_weight_head_circumference.htm
Centers for Disease Control and Prevention, 2010, “ Data Table for Girls Weight-for-Length and Head Circumference-for-Age Charts,” Last accessed June 18, 2015, http://www.cdc.gov/growthcharts/who/girls_weight_head_circumference.htm
Sorbe, B. , and Dahlgren, S. , 1983, “ Some Important Factors in the Molding of the Fetal Head During Vaginal Delivery—A Photographic Study,” Int. J. Gynaecol. Obstet., 21(3), pp. 205–212. [CrossRef] [PubMed]
Baxter, J. , 1946, “ Moulding of the Foetal Head: A Compensatory Mechanism,” J. Obstet. Gynaecol. Br. Emp., 53(3), pp. 212–218. [CrossRef] [PubMed]
Kriewall, T. J. , Stys, S. J. , and McPherson, G. K. , 1977, “ Neonatal Head Shape After Delivery: An Index of Molding,” J. Perinat. Med., 5(6), pp. 260–267. [CrossRef] [PubMed]
Moloy, H. C. , 1942, “ Studies on Head Molding During Labor,” Am. J. Obstet. Gynecol., 76, pp. 762–782. [CrossRef]
Gardberg, M. , and Tuppurainen, M. , 1994, “ Persistent Occiput Posterior Presentation—A Clinical Problem,” Acta Obstet. Gynecol. Scand., 73(1), pp. 45–47. [CrossRef] [PubMed]
Borell, U. , and Fernstrom, I. , 1958, “ Die Umformung des Kindlichen Kopfes Wahrend Normaler Entbingen in Regelrechter Hinterhauptslag,” Geburtshilfe Frauenheilkd., 18(9), pp. 1156–1166. [PubMed]
Lowder, J. , Burrows, L. , Krohn, M. , and Weber, A. , 2007, “ Risk Factors for Primary and Subsequent Anal Sphincter Lacerations: A Comparison of Cohorts by Parity and Prior Mode of Delivery,” Am. J. Obstet. Gynecol., 196(4), pp. 344–348. [CrossRef] [PubMed]
Jing, D. , 2010, “ Experimental and Theoretical Biomechanical Analyses of the Second Stage of Labor,” Last accessed Aug. 21, 2015, http://deepblue.lib.umich.edu/handle/2027.42/76013
Lowder, J. L. , Debes, K. M. , Moon, D. K. , Howden, N. , Abramowitch, S. D. , and Moalli, P. A. , 2007, “ Biomechanical Adaptations of the Rat Vagina and Supportive Tissues in Pregnancy to Accommodate Delivery,” Obstet. Gynecol., 109(1), pp. 136–143. [CrossRef] [PubMed]
Kriewall, T. J. , 1982, “ Structural, Mechanical, and Material Properties of Fetal Cranial Bone,” Am. J. Obstet. Gynecol., 143(6), pp. 707–714. [PubMed]
Margulies, S. S. , and Thibault, K. L. , 2000, “ Infant Skull and Suture Properties: Measurements and Implications for Mechanisms of Pediatric Brian Injury,” ASME J. Biomech. Eng., 122(4), pp. 364–371. [CrossRef]
Ergaz, U. , Goldstein, I. , Divon, M. , and Weiner, Z. , 2015, “ A Preliminary Study of Three-Dimensional Sonographic Measurements of the Fetus,” Rambam Maimonides Med. J., 6(2), p. e0019. [CrossRef] [PubMed]
Maharaj, D. , 2010, “ Assessing Cephalopelvic Disproportion: Back to the Basics,” Obstet. Gynecol. Surv., 65(6), pp. 387–395. [CrossRef] [PubMed]
Beckmann, M. M. , and Stock, O. M. , 2013, “ Antenatal Perineal Massage for Reducing Perineal Trauma,” Cochrane Database Syst. Rev., 4, p. CD005123. [PubMed]
Grobman, W. , Lai, Y. , Landon, M. , Spong, C. , Leveno, K. , Rouse, D. , Varner, M. , Moawad, A. , Caritis, S. , Harper, M. , Wapner, R. , Sorokin, Y. , Miodovnik, M. , Carpenter, M. , O'Sullivan, M. , Sibai, B. , Langer, O. , Thorp, J. , Ramin, S. , Mercer, B. , and NICHD, 2007, “ Development of a Nomogram for Prediction of Vaginal Birth After Cesarean Delivery,” Obstet. Gynecol., 109(4), pp. 806–812. [CrossRef] [PubMed]
Siafarikas, F. , Staer-Jensen, J. , Hilde, G. , Bö, K. , and Ellstrom, E. M. , 2014, “ Levator Hiatus Dimensions in Late Pregnancy and the Process of Labor: A 3- and 4-Dimensional Transperinael Ultrasound Study,” Am. J. Obstet. Gynecol., 210(5), pp. 484–491. [CrossRef] [PubMed]

Figures

Grahic Jump Location
Fig. 1

Schematic illustration of the LA muscles. The subcomponents of the PVM (PPM; PAM, and PVaM) are shown. Left: schematic view of the LA muscles from below after the vulvar structures and PM have been removed showing the arcus tendineus levator ani (ATLA); external anal sphincter (EAS); PAM; PB uniting the two ends of the PPM; ICM; PRM. Right: the LA muscle seen from above looking over the sacral promontory (SAC) showing the PVaM. The urethra, vagina, and rectum have been transected just above the pelvic floor. (The internal obturator muscles have been removed to clarify levator muscle origins.) Recently, it has become clear that the origin of the PRM lies more caudal than is suggested in the illustration at left [8]. Copyright © DeLancey 2003 [9].

Grahic Jump Location
Fig. 2

Upper left: left lateral view of 3D model of the pelvis (green), showing the high origin location (arrow) of the PVM (orange) and the PVM insertion on the PB/AS (light blue). Upper right: 3D model of the pelvis (green), showing the PRM (dark purple, lower right of that image) originating from the PM (white). In the upper two figures, A, P, L, R, and I denote anterior, posterior, left, right, and inferior, respectively. Lower left: The pubic symphysis is projected in the sagittal view seen in a view from the left showing a downward rotation of the PVM loop. Note the wrapping of the PVM around the inferior pubic ramus at point 2 at ultimate crowning. The portion of the PVM between points 1 and 2 lying above the inferior pubic ramus point, 2, is the “noncontact” length because it cannot contact and encircle the fetal head due to the rigidity of the pubic bone. That part of the PVM lying between points 2 and 3 lies below the pubic ramus at 2 so it can contact and encircle the fetal head to allow it to pass inside the loop formed by the PVM. Lower right: This illustrates the downward rotation of the PRM from the prelabor to the ultimate crowning position. Note the absence of PRM wrapping.

Grahic Jump Location
Fig. 3

Caudal view of anterior pelvis with variables used in the maternal capacity calculations. The soft tissue loop originates high on the pelvis (filled arrow heads) and wraps around the fetal head (gray circular structure). The portion of the soft tissue loop in contact with the fetal head is represented by the thick black band, while the portion not in contact with the fetal head is represented by the dashed lines. θ = SPAA. Arch = pelvis/subpubic arch.

Grahic Jump Location
Fig. 4

Graphic illustration of the sensitivity analyses in caudal view. Top: Nominal configuration using the convention in Fig.3. Middle left: varying SL (thick black band). Middle right: varying soft tissue origin placement on pelvis (black arrow heads). Bottom left: varying SPAA. Bottom right: varying head size (gray circle). The variation in soft tissue length reduction in downward rotation is not shown. Factors were varied by ± 10%.

Grahic Jump Location
Fig. 5

Cranial and right side views of the fetal head showing the SD, MD, BD, and FD. Figure adapted from Sobre et al. [24].

Grahic Jump Location
Fig. 6

Vertex presentation. Male fetal head circumference (in mm) presenting to the birth canal in a vertex presentation. The shading (green) or the diagonal indicates a region of equal population distribution values for molding and head size. The intensity of the (blue) shading at lower left indicates the degree of maximal molding of small fetal heads, while the intensity of the (red) shading at upper right indicates the degree of lack of molding of large fetal heads.

Grahic Jump Location
Fig. 7

Predicted maternal capacity-to-fetal head demand ratio, g, for the PVM loop with wrapping. The intensity of the (red) shading indicates the degree of cephalolevator disproportion for the PVM.

Grahic Jump Location
Fig. 8

Predicted maternal capacity-to-fetal head demand ratio, g, for the PRM loop. The intensity of (red) shading indicates the degree of cephalolevator disproportion for the PRM.

Grahic Jump Location
Fig. 9

Face presentation. Male fetal head circumference (in mm) presenting to the birth canal during face presentation. The shading (green) of the diagonal indicates a region of equal population distribution values for molding and head size. The intensity of the (blue) shading at lower left indicates the degree of maximal molding of small fetal heads, while the intensity of (red) shading at upper right indicates the degree of lack of molding of large fetal heads.

Grahic Jump Location
Fig. 10

Predicted maternal capacity-to-fetal head demand ratio, g, for the PVM loop without wrapping. The intensity of the (red) shading indicates the degree of cephalolevator disproportion for the PVM in this special case.

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