Effects of Fetal Head Motion on Pelvic Floor Mechanics

Pelvic Floor Disorders 6 Months after Attempted Operative Vaginal Delivery According to the Fetal Head Station: A Prospective Cohort Study

PLoS ONE ◽

10.1371/journal.pone.0168591 ◽

2016 ◽

Vol 11 (12) ◽

pp. e0168591 ◽

Cited By ~ 2

Author(s):

Guillaume Ducarme ◽

Jean-François Hamel ◽

Stéphanie Brun ◽

Hugo Madar ◽

Benjamin Merlot ◽

...

Keyword(s):

Cohort Study ◽

Pelvic Floor ◽

Vaginal Delivery ◽

Prospective Cohort Study ◽

Prospective Cohort ◽

Pelvic Floor Disorders ◽

Fetal Head ◽

Operative Vaginal Delivery

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Transperineal ultrasound assessment of maternal pelvic floor at term and fetal head engagement

Ultrasound in Obstetrics and Gynecology ◽

10.1002/uog.21982 ◽

2020 ◽

Vol 56 (6) ◽

pp. 921-927 ◽

Cited By ~ 1

Author(s):

A. Youssef ◽

E. Brunelli ◽

E. Montaguti ◽

G. Di Donna ◽

M. G. Dodaro ◽

...

Keyword(s):

Pelvic Floor ◽

Transperineal Ultrasound ◽

Fetal Head ◽

Ultrasound Assessment

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Biomechanical trade-offs in the pelvic floor constrain the evolution of the human birth canal

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2022159118 ◽

2021 ◽

Vol 118 (16) ◽

pp. e2022159118 ◽

Cited By ~ 1

Author(s):

Ekaterina Stansfield ◽

Krishna Kumar ◽

Philipp Mitteroecker ◽

Nicole D. S. Grunstra

Keyword(s):

Pelvic Floor ◽

Element Model ◽

Original Position ◽

Abdominal Pressure ◽

Fetal Head ◽

Birth Canal ◽

Trade Offs ◽

Resistance To Deformation ◽

Inner Organs ◽

Tissue Stresses

Compared with most other primates, humans are characterized by a tight fit between the maternal birth canal and the fetal head, leading to a relatively high risk of neonatal and maternal mortality and morbidities. Obstetric selection is thought to favor a spacious birth canal, whereas the source for opposing selection is frequently assumed to relate to bipedal locomotion. Another, yet underinvestigated, hypothesis is that a more expansive birth canal suspends the soft tissue of the pelvic floor across a larger area, which is disadvantageous for continence and support of the weight of the inner organs and fetus. To test this “pelvic floor hypothesis,” we generated a finite element model of the human female pelvic floor and varied its radial size and thickness while keeping all else constant. This allowed us to study the effect of pelvic geometry on pelvic floor deflection (i.e., the amount of bending from the original position) and tissue stresses and stretches. Deflection grew disproportionately fast with increasing radial size, and stresses and stretches also increased. By contrast, an increase in thickness increased pelvic floor stiffness (i.e., the resistance to deformation), which reduced deflection but was unable to fully compensate for the effect of increasing radial size. Moreover, larger thicknesses increase the intra-abdominal pressure necessary for childbirth. Our results support the pelvic floor hypothesis and evince functional trade-offs affecting not only the size of the birth canal but also the thickness and stiffness of the pelvic floor.

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832: Pelvic floor disorders 6 months after attempted operative vaginal delivery according to the fetal head station

American Journal of Obstetrics and Gynecology ◽

10.1016/j.ajog.2015.10.882 ◽

2016 ◽

Vol 214 (1) ◽

pp. S433

Author(s):

Guillaume Ducarme ◽

Jean François Hamel ◽

Stephanie Brun ◽

Hugo Madar ◽

Frederic Coatleven ◽

...

Keyword(s):

Pelvic Floor ◽

Vaginal Delivery ◽

Pelvic Floor Disorders ◽

Fetal Head ◽

Operative Vaginal Delivery

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

Journal of Biomechanical Engineering ◽

10.1115/1.4032424 ◽

2016 ◽

Vol 138 (2) ◽

Cited By ~ 17

Author(s):

Paige V. Tracy ◽

John O. DeLancey ◽

James A. Ashton-Miller

Keyword(s):

Soft Tissue ◽

Pelvic Floor ◽

Separation Distance ◽

Demand Analysis ◽

Head Size ◽

Levator Muscle ◽

Muscle Injuries ◽

Fetal Head ◽

Stretch Injury ◽

Geometric Ratio

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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Effects of Nonlinear Muscle Elasticity on Pelvic Floor Mechanics During Vaginal Childbirth

Journal of Biomechanical Engineering ◽

10.1115/1.4002558 ◽

2010 ◽

Vol 132 (11) ◽

Cited By ~ 24

Author(s):

Xinshan Li ◽

Jennifer A. Kruger ◽

Martyn P. Nash ◽

Poul M. F. Nielsen

Keyword(s):

Experimental Data ◽

Pelvic Floor ◽

Vaginal Delivery ◽

Pelvic Floor Dysfunction ◽

Levator Ani ◽

Head Model ◽

Levator Ani Muscle ◽

Fetal Head ◽

Second Stage Of Labor ◽

Second Stage

The role of the pelvic floor soft tissues during the second stage of labor, particularly the levator ani muscle, has attracted much interest recently. It has been postulated that the passage of the fetal head through the pelvis may cause excessive stretching of the levator ani muscle, which may lead to pelvic floor dysfunction and pelvic organ prolapse later in life. In order to study the complex biomechanical interactions between the levator ani muscle and the fetal head during the second stage of labor, finite element models have been developed for quantitative analysis of this process. In this study we have simulated vaginal delivery using individual-specific anatomical computer models of the pelvic floor interacting with a fetal head model with minimal restrictions placed upon its motion. Two constitutive relations were considered for the levator ani muscle (of exponential and neo-Hookean forms). For comparison purposes, the exponential relation was chosen to exhibit much greater stiffening at higher strains beyond the range of the experimental data. We demonstrated that increased nonlinearity in the elastic response of the tissues leads to considerably higher (56%) estimated force required for delivery, accompanied by a more homogeneous spatial distribution of maximum principal stretch ratio across the muscle. These results indicate that the form of constitutive relation beyond the presently available experimental data markedly affects the estimated function of the levator ani muscle during vaginal delivery, due to the large strains that occur. Further experimental data at higher strains are necessary in order to more reliably characterize the constitutive behavior required for modeling vaginal childbirth.

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