Background
During the second stage of labor, the maternal pelvic floor muscles undergo repetitive
stretch loading as uterine contractions and strenuous maternal pushes combined to
expel the fetus, and it is not uncommon that these muscles sustain a partial or complete
rupture. It has recently been demonstrated that soft tissues, including the anterior
cruciate ligament and connective tissue in sheep pelvic floor muscle, can accumulate
damage under repetitive physiological (submaximal) loads. It is well known to material
scientists that this damage accumulation can not only decrease tissue resistance to
stretch but also result in a partial or complete structural failure. Thus, we wondered
whether certain maternal pushing patterns (in terms of frequency and duration of each
push) could increase the risk of excessive damage accumulation in the pelvic floor
tissue, thereby inadvertently contributing to the development of pelvic floor muscle
injury.
Objective
This study aimed to determine which labor management practices (spontaneous vs directed
pushing) are less prone to accumulate damage in the pelvic floor muscles during the
second stage of labor and find the optimum approach in terms of minimizing the risk
of pelvic floor muscle injury.
Study Design
We developed a biomechanical model for the expulsive phase of the second stage of
labor that includes the ability to measure the damage accumulation because of repetitive
physiological submaximal loads. We performed 4 simulations of the second stage of
labor, reflecting a directed pushing technique and 3 alternatives for spontaneous
pushing.
Results
The finite element model predicted that the origin of the pubovisceral muscle accumulates
the most damage and so it is the most likely place for a tear to develop. This result
was independent of the pushing pattern. Performing 3 maternal pushes per contraction,
with each push lasting 5 seconds, caused less damage and seemed the best approach.
The directed pushing technique (3 pushes per contraction, with each push lasting 10
seconds) did not reduce the duration of the second stage of labor and caused higher
damage accumulation.
Conclusion
The frequency and duration of the maternal pushes influenced the damage accumulation
in the passive tissues of the pelvic floor muscles, indicating that it can influence
the prevalence of pelvic floor muscle injuries. Our results suggested that the maternal
pushes should not last longer than 5 seconds and that the duration of active pushing
is a better measurement than the total duration of the second stage of labor. Hopefully,
this research will help to shed new light on the best practices needed to improve
the experience of labor for women.
Key words
To read this article in full you will need to make a payment
Purchase one-time access:
Academic & Personal: 24 hour online accessCorporate R&D Professionals: 24 hour online accessOne-time access price info
- For academic or personal research use, select 'Academic and Personal'
- For corporate R&D use, select 'Corporate R&D Professionals'
Subscribe:
Subscribe to American Journal of Obstetrics & GynecologyAlready a print subscriber? Claim online access
Already an online subscriber? Sign in
Register: Create an account
Institutional Access: Sign in to ScienceDirect
References
- Association of pubovisceral muscle tear with functional capacity of urethral closure: evaluating maternal recovery from labor and delivery.Am J Obstet Gynecol. 2020; 222: 598.e1-598.e7
- The appearance of levator ani muscle abnormalities in magnetic resonance images after vaginal delivery.Obstet Gynecol. 2003; 101: 46-53
- Avulsion of the pubovisceral muscle associated with large vaginal tear after normal vaginal delivery at term.Aust N Z J Obstet Gynaecol. 2007; 47: 341-344
- Comparison of the puborectal muscle on MRI in women with POP and levator ani defects with those with normal support and no defect.Int Urogynecol J. 2012; 23: 73-77
- Origin and insertion points involved in levator ani muscle defects.Am J Obstet Gynecol. 2007; 196: 251.e1-251.e5
- Intrapartum risk factors for levator trauma.BJOG. 2010; 117: 1485-1492
- Evaluating maternal recovery from labor and delivery: bone and levator ani injuries.Am J Obstet Gynecol. 2015; 213: 188.e1-188.e11
- Prevalence of levator ani muscle injury in Chinese women after first delivery.Ultrasound Obstet Gynecol. 2012; 39: 704-709
- Does the Epi-No(®) birth trainer prevent vaginal birth-related pelvic floor trauma? A multicentre prospective randomised controlled trial.BJOG. 2016; 123: 995-1003
- Post-partum pelvic floor dysfunction assessed on 3D rotational ultrasound: a prospective study on women with first- and second-degree perineal tears and episiotomy.J Matern Fetal Neonatal Med. 2021; 34: 445-455
- On the biomechanics of vaginal birth and common sequelae.Annu Rev Biomed Eng. 2009; 11: 163-176
- Procedures for pelvic organ prolapse in the United States, 1979-1997.Am J Obstet Gynecol. 2003; 188: 108-115
- Anterior cruciate ligament fatigue failures in knees subjected to repeated simulated pivot landings.Am J Sports Med. 2013; 41: 1058-1066
- New perspectives on ACL injury: on the role of repetitive sub-maximal knee loading in causing ACL fatigue failure.J Orthop Res. 2016; 34: 2059-2068
- On the heterogeneity of the femoral enthesis of the human ACL: microscopic anatomy and clinical implications.J Exp Orthop. 2016; 3: 14
- An anterior cruciate ligament failure mechanism.Am J Sports Med. 2019; 47: 2067-2076
- Injuries in muscle-tendon-bone units: a systematic review considering the role of passive tissue fatigue.Orthop J Sports Med. 2021; 923259671211020731
- The role of fatigue in susceptibility to acute muscle strain injury.Am J Sports Med. 1996; 24: 137-143
- Identification of a threshold for skeletal muscle injury.Am J Sports Med. 1994; 22: 257-261
- Experimental muscle strain injury. Early functional and structural deficits and the increased risk for reinjury.Am J Sports Med. 1993; 21: 190-194
- The effects of cyclic stretching on tensile properties of the rabbit’s skeletal muscle.Clin Biomech (Bristol, Avon). 1998; 13: 48-53
- Investigating the birth-related caudal maternal pelvic floor muscle injury: the consequences of low cycle fatigue damage.J Mech Behav Biomed Mater. 2020; 110: 103956
- Biomechanical analysis of low-cycle fatigue damage during the second stage of labor.([Doctoral dissertation]) Department of Mechanical Engineering, University of Porto, Portugal2022
- Beckmann and Ling’s obstetrics and gynecology.8th ed. Wolters Kluwer, Philadelphia, PA2019
- Maternal and neonatal outcomes from a comparison of spontaneous and directed pushing in second stage.Women Birth. 2019; 32: e433-e440
- Efficacy of spontaneous pushing with pursed lips breathing compared with directed pushing in maternal and neonatal outcomes.J Obstet Gynaecol. 2021; ([Epub ahead of print])
- Second-stage labor care: challenges in spontaneous bearing down.J Perinat Neonatal Nurs. 2009; 23: 31-41
- A randomized trial of the effects of coached vs uncoached maternal pushing during the second stage of labor on postpartum pelvic floor structure and function.Am J Obstet Gynecol. 2005; 192: 1692-1696
- The “push” for evidence: management of the second stage.J Midwifery Womens Health. 2002; 47: 2-15
- Biomechanical analyses of the efficacy of patterns of maternal effort on second-stage progress.Obstet Gynecol. 2009; 113: 873-880
- Pushing/bearing down methods for the second stage of labour.Cochrane Database Syst Rev. 2017; 3: CD009124
- A comparison of two bearing-down techniques during the second stage of labor.J Nurse Midwif. 1984; 29: 3-11
- The effect of maternal bearing-down efforts on arterial umbilical cord pH and length of the second stage of labor.J Nurse Midwifery. 1992; 37: 61-63
- Spontaneous pushing during birth. Relationship to perineal outcomes.J Nurse Midwifery. 1999; 44: 36-39
- Pushing techniques in the second stage of labour.J Adv Nurs. 1993; 18: 171-177
- Infant outcome in relation to second stage labor pushing method.Birth. 1982; 9: 221-229
- Effects of pushing techniques during the second stage of labor: a randomized controlled trial.Taiwan J Obstet Gynecol. 2017; 56: 606-612
- Pelvic floor muscle injury during a difficult labor. Can tissue fatigue damage play a role?.Int Urogynecol J. 2022; 33: 211-220
- Levator ani muscle stretch induced by simulated vaginal birth.Obstet Gynecol. 2004; 103: 31-40
- Deformation of the pelvic floor muscles during a vaginal delivery.Int Urogynecol J Pelvic Floor Dysfunct. 2008; 19: 65-71
- A biomechanical analysis on the impact of episiotomy during childbirth.Biomech Model Mechanobiol. 2016; 15: 1523-1534
- The management of episiotomy technique and its effect on pelvic floor muscles during a malposition childbirth.Comput Methods Biomech Biomed Engin. 2017; 20: 1249-1259
- Computational modeling approach to study the effects of fetal head flexion during vaginal delivery.Am J Obstet Gynecol. 2010; 203: 217.e1-217.e6
- Viscous effects in pelvic floor muscles during childbirth: a numerical study.Int J Numer Method Biomed Eng. 2018; 34
- The influence of an occipito-posterior malposition on the biomechanical behavior of the pelvic floor.Eur J Obstet Gynecol Reprod Biol. 2009; 144: S166-S169
- A numerical study on fetal head molding during labor.Int J Numer Method Biomed Eng. 2021; 37: e3411
- Measuring morphological parameters of the pelvic floor for finite element modelling purposes.J Biomech. 2003; 36: 749-757
- Experimental and theoretical biomechanical analyses of the second stage of labor.([Doctoral dissertation]) Department of Mechanical Engineering, University of Michigan, Ann Arbor2010
- The effect of pregnancy on hiatal dimensions and urethral mobility: an observational study.Int Urogynecol J. 2012; 23: 1561-1567
- Pelvic floor changes in the first term pregnancy and postpartum period.Int Urogynecol J. 2021; 32: 1897-1905
- The World Health Organization fetal growth charts: a multinational longitudinal study of ultrasound biometric measurements and estimated fetal weight.PLoS Med. 2017; 14e1002220
- A new constitutive framework for arterial wall mechanics and a comparative study of material models.J Elast Phys Sci Solids. 2000; 61: 1-48
- A viscoelastic model for fiber-reinforced composites at finite strains: continuum basis, computational aspects and applications.Comput Methods Appl Mech Eng. 2001; 190: 4379-4403
- A general framework for the numerical implementation of anisotropic hyperelastic material models including non-local damage.Biomech Model Mechanobiol. 2017; 16: 1119-1140
- Simulating uterine contraction by using an electro-chemo-mechanical model.Biomech Model Mechanobiol. 2016; 15: 497-510
- Biomechanical simulation of the fetal descent without imposed theoretical trajectory.Comput Methods Programs Biomed. 2013; 111: 389-401
- Pressures on the fetal head during normal labor.J Perinat Med. 1991; 19: 199-206
- A randomized trial of coached versus uncoached maternal pushing during the second stage of labor.Am J Obstet Gynecol. 2006; 194: 10-13
- Evidence-based management of the second stage of labor.Semin Perinatol. 2020; 44: 151213
- The second stage of labor.Best Pract Res Clin Obstet Gynaecol. 2020; 67: 53-64
- Pubococcygeus-puborectalis trauma after forceps delivery: evaluation of the levator ani muscle with 3D/4D ultrasound.Int Urogynecol J Pelvic Floor Dysfunct. 2009; 20: 1175-1181
- Duration of spontaneous labour in ‘low-risk’ women with ‘normal’ perinatal outcomes: a systematic review.Eur J Obstet Gynecol Reprod Biol. 2018; 223: 123-132
- The influence of maternal bearing-down efforts during second stage on fetal well-being.Birth. 1979; 6: 17-21
- The effect of maternal pushing on fetal cerebral oxygenation and blood volume during the second stage of labour.Br J Obstet Gynaecol. 1995; 102: 448-453
- Minimizing fatigue during repetitive jobs: optimal work-rest schedules.Hum Factors. 1997; 39: 83-101
- Central fatigue contributes to the greater reductions in explosive than maximal strength with high-intensity fatigue.Exp Physiol. 2014; 99: 964-973
- Modification of a three-compartment muscle fatigue model to predict peak torque decline during intermittent tasks.J Biomech. 2018; 77: 16-25
- Predicting birth-related levator ani tear severity in primiparous women: evaluating maternal recovery from labor and delivery (EMRLD study).Open J Obstet Gynecol. 2014; 4: 266-278
- Sample size determination and power analysis using the G∗Power software.J Educ Eval Health Prof. 2021; 18: 17
- Aging effects on pelvic floor support: a pilot study comparing young versus older nulliparous women.Int Urogynecol J. 2020; 31: 535-543
- Pelvic floor shape variations during pregnancy and after vaginal delivery.Comput Methods Programs Biomed. 2020; 194: 105516
- On the variation in maternal birth canal in vivo viscoelastic properties and their effect on the predicted length of active second stage and levator ani tears.J Biomech. 2018; 74: 64-71
- Finite element modeling of maximum stress in pelvic floor structures during the head expulsion (FINESSE) study.Int Urogynecol J. 2021; 32: 1997-2003
- Anatomy of the pubovisceral muscle origin: macroscopic and microscopic findings within the injury zone.Neurourol Urodyn. 2015; 34: 774-780
Supplemental References
Dassault Systemes Simulia Corporation, Abaqus V. 6.14 Documentation.
- Constitutive modeling of soft tissues.in: Narayan R. Encyclopedia of biomedical engineering. Elsevier, Oxford, United Kingdom2019: 81-110
- Nonlinear solid mechanics: a continuum approach for engineering.John Wiley & Sons, Chichester, England2000
- Computational aspects of the numerical modelling of softening, damage and permanent set in soft biological tissues.Comput Struct. 2014; 130: 57-72
- Milella P.P. Milella P.P. Fatigue and corrosion in metals. 1st ed. Springer-Verlag Mailand, Italian Republic2013
- A ductile damage nonlocal model of integral-type at finite strains: formulation and numerical issues.Int J Damage Mech. 2011; 20: 515-557
- Nonlocal integral formulations of plasticity and damage: survey of progress.J Eng Mech. 2002; 128: 1119-1149
Article Info
Publication History
Published online: January 28, 2022
Accepted:
January 14,
2022
Received in revised form:
January 7,
2022
Received:
July 8,
2021
Footnotes
J.A.A.M.’s institution received a US National Institutes of Health grant (grant number R44 HD 096987) for him and a student to analyze the Materna LLC Prep device data on the relationship between birth canal dilation force and displacement during the first stage of labor. That research did not address any topics found in the current paper. The remaining authors report no conflict of interest.
The authors acknowledge the support from the Portuguese Foundation of Science under grant number SFRH/BD/136213/2018 and under the research project UIDB/50022/2020. The funding sources were not involved in preparing the manuscript and conducting the research.
Cite this article as: Vila Pouca MCP, Ferreira JPS, Parente MPL, et al. On the management of maternal pushing during the second stage of labor: a biomechanical study considering passive tissue fatigue damage accumulation. Am J Obstet Gynecol 2022;227:267.e1-20.
Identification
Copyright
© 2022 Elsevier Inc. All rights reserved.
