Fetal head size and effect of manual perineal protection

On the uncertainty quantification of the active uterine contraction during the second stage of labor simulation

Uterine contractions in the myometrium occur at multiple scales, spanning both organ and cellular levels. This complex biological process plays an essential role in the fetus delivery during the second stage of labor. Several finite element models of active uterine contractions have already been developed to simulate the descent of the fetus through the birth canal. However, the developed models suffer severe reliability issues due to the uncertain parameters. In this context, the present study aimed to perform the uncertainty quantification (UQ) of the active uterine contraction simulation to advance our understanding of pregnancy mechanisms with more reliable indicators. A uterus model with and without fetus was developed integrating a transversely isotropic Mooney-Rivlin material with two distinct fiber orientation architectures. Different contraction patterns with complex boundary conditions were designed and applied. A global sensitivity study was performed to select the most valuable parameters for the uncertainty quantification (UQ) process using a copula-based Monte Carlo method. As results, four critical material parameters (C 1 , C 2 , K , Ca 0 ) of the active uterine contraction model were identified and used for the UQ process. The stress distribution on the uterus during the fetus descent, considering first and second fiber orientation families, ranged from 0.144 to 1.234 MPa and 0.044 to 1.619 MPa, respectively. The simulation outcomes revealed also the segment-specific contraction pattern of the uterus tissue. The present study quantified, for the first time, the effect of uncertain parameters of the complex constitutive model of the active uterine contraction on the fetus descent process. As perspectives, a full maternal pelvis model will be coupled with reinforcement learning to automatically identify the delivery mechanism behind the cardinal movements of the fetus during the active expulsion process.

Neonatal head circumference as a risk factor for obstetric anal sphincter injuries: a systematic review and meta-analysis

OBJECTIVE

Between 53% and 79% of women will sustain some degree of perineal laceration during vaginal delivery. Third- and fourth-degree perineal lacerations are known as obstetric anal sphincter injuries. Timely diagnosis and prompt treatment of obstetric anal sphincter injuries can help to prevent the development of severe consequences like fecal incontinence, urinary incontinence, and rectovaginal fistula. Neonatal head circumference is routinely measured postpartum but is often not mentioned as a risk factor for obstetric anal sphincter injuries in clinical guidelines. Thus far, no review article on the risk factors for obstetric anal sphincter injuries has discussed the role of neonatal head circumference. This study aimed to review and analyze the relationship between head circumference and the occurrence of obstetric anal sphincter injuries among previous studies to conclude whether head circumference should be recognized as an important risk factor.

DATA SOURCES

Through study screening on Google Scholar, PubMed, Scopus, and Science Direct for articles published between 2013 to 2023, followed by assessment of eligibility, this study ended up reviewing 25 studies, 17 of which were included in the meta-analysis.

STUDY ELIGIBILITY CRITERIA

Only studies that reported both the neonatal head circumference and the occurrence of obstetric anal sphincter injuries were included in this review.

METHODS

The included studies were appraised using the Dartmouth Library risk of bias assessment checklist. Qualitative synthesis was based on the study population, findings, adjusted confounding factors, and suggested causative links in each study. Quantitative synthesis was conducted using calculation and pooling of odds ratios and inverse variance using Review Manager 5.4.1.

RESULTS

A statistically significant association between head circumference and obstetric anal sphincter injuries was reported in 21 of 25 studies; 4 studies reported that head circumference was a true independent risk factor. A meta-analysis of the studies that reported neonatal head circumference as a dichotomous categorical variable with a cutoff point of 35±1 cm yielded statistically significant pooled results (odds ratio, 1.92; 95% confidence interval, 1.80-2.04).

CONCLUSION

The risk for obstetric anal sphincter injuries increased as the neonatal head circumference increased-this should be considered in decision-making during labor and postpartum management to attain the best outcome.

A Computational Procedure to Derive the Curve of Carus for Childbirth Computational Modeling

Computational modeling serves an important role in childbirth-related research. Prescribed fetal descent trajectory is a key characteristic in childbirth simulations. Two major types of fully prescribed fetal descent trajectory can be identified in the literature: straight descent trajectories and curve of Carus. The straight descent trajectory has the advantage of being simpler and could serve as a reasonable approximation for relatively small fetal movements during labor, but it cannot be used to simulate the entire childbirth process. Curve of Carus is the well-recognized fetal descent trajectory with physiological significance. However, no mathematical description of the curve of Carus can be found in the existing computational studies. This status of curve of Carus simulation in the literature hinders the direct comparison of results across different studies and the advancement of computational techniques built upon previous research. The goals of this study are: (1) propose a universal approach to achieve the curve of Carus for the second stage of labor, from the point when the fetal head engages the pelvis to the point when the fetal head is fully delivered. (2) demonstrate its utility when considering various fetal head sizes. The current study provides a detailed formulation of the curve of Carus, considering geometries of both the mother and the fetus. The maternal geometries were obtained from MRI data, and the fetal head geometries were based on laser scanning of a replica of a real fetal head.

Investigating the Effects of Different Sizes of Silicone Rubber Vacuum Extractors during the Course of Delivery on the Fetal Head: A Finite Element Analysis Study

During certain clinical situations, some parturients require instruments for operative vaginal delivery, and various designs of vacuum extractors may affect the fetal head. To investigate the biomechanical effects of divergent sizes of silicone rubber vacuum extractors, we employed finite element analysis in this study. First, we constructed computer models for different vacuum extractor sizes (diameters: 40 mm, 50 mm, 60 mm, and 70 mm), flat surface, hemispherical ball, and fetal head shape. A hemispherical ball was the main design for the vacuum extractor model, and the material used for the vacuum extractor was silicone rubber. Next, the settings of 1 mm vacuum extractor displacement and vacuum cap pressure of 60 cmHg were applied. The main observation markers of this study were the respective von Mises stresses on the vacuum extractor and skull by the reaction force on the fixed end. The concluded results revealed that vacuum extractors with larger diameters lead to greater reaction force, stress, and strain on fetal heads. Therefore, this study’s biomechanical analytic consequences suggest that clinicians avoid selecting larger vacuum extractors during operative instrumental delivery so that fetal heads will experience less external force, deformation, and resultant complications. It could also provide a practical reference for obstetricians for instrumental vaginal delivery with the vacuum extractor made of silicone rubber.

Musculoskeletal lower back load of accoucheurs during childbirth - A pilot and feasibility study

INTRODUCTION

Back problems represent one of the leading causes of accouchers' work-related musculoskeletal morbidities. The correct execution of birth-related maneuvers including manual perineal protection is crucial not only for the mother and child but also for obstetricians and midwives to reduce any strain on their musculoskeletal system. Therefore, the overall aim of this study was to test the feasibility of determining the effect of different accouchers' postures (standing and kneeling) on their musculoskeletal system.

METHODS

The biomechanical analysis is based on musculoskeletal simulations that included motion recordings of real deliveries as well as deliveries conducted on a birthing simulator. These simulations were then used to determine individual joints' loads.

RESULTS

In the kneeling posture, both a low intra-operator variability and a lower average maximum load of the lower back was observed. For the standing position the spine load was reduced by pivoting the elbow on the accouchers' thigh, which in turn was associated with a significantly greater load on the shoulder joint.

CONCLUSION

The study demonstrated the feasibility of our technique to assess joints loads. It also provided initial data indicating that a posture that reduces spinal flexion and tilt, achieved in this study by the kneeling, can significantly reduce the strain on the practitioner's musculoskeletal system.

Childbirth Computational Models: Characteristics and Applications

The biomechanical process of childbirth is necessary to usher in new lives-but it can also result in trauma. This physically intense process can put both the mother and the child at risk of injuries and complications that have life-long impact. Computational models, as a powerful tool to simulate and explore complex phenomena, have been used to improve our understanding of childbirth processes and related injuries since the 1990s. The goal of this paper is to review and summarize the breadth and current state of the computational models of childbirth in the literature-focusing on those that investigate the mechanical process and effects. We first summarize the state of critical characteristics that have been included in computational models of childbirth (i.e., maternal anatomy, fetal anatomy, cardinal movements, and maternal soft tissue mechanical behavior). We then delve into the findings of the past studies of birth processes and mechanical injuries in an effort to bridge the gap between the theoretical, numerical assessment and the empirical, clinical observations and practices. These findings are from applications of childbirth computational models in four areas: (1) the process of childbirth itself, (2) maternal injuries, (3) fetal injuries, and (4) protective measures employed by clinicians during delivery. Finally, we identify some of the challenges that computational models still face and suggest future directions through which more biofidelic simulations of childbirth might be achieved, with the goal that advancing models may provide more efficient and accurate, patient-specific assessment to support future clinical decision-making.

Finite element modeling of maximum stress in pelvic floor structures during the head expulsion (FINESSE) study

INTRODUCTION AND HYPOTHESIS

Several studies have assessed birth-related deformations of the levator ani muscle (LAM) and perineum on models that depicted these elements in isolation. The main aim of this study was to develop a complex female pelvic floor computational model using the finite element method to evaluate points and timing of maximum stress at the LAM and perineum in relation to the birth process.

METHODS

A three-dimensional computational model of the female pelvic floor was created and used to simulate vaginal birth based on data from previously described real-life MRI scans. We developed three models: model A (LAM without perineum); model B (perineum without LAM); model C (a combined model with both structures).

RESULTS

The maximum stress in the LAM was achieved when the vertex was 9 cm below the ischial spines and measured 37.3 MPa in model A and 88.7 MPa in model C. The maximum stress in the perineum occurred at the time of distension by the suboocipito-frontal diameter and reached 86.7 MPa and 119.6 MPa in models B and C, respectively, while the stress in the posterior fourchette caused by the suboccipito-bregmatic diameter measured 36.9 MPa for model B and 39.8 MPa for model C.

CONCLUSIONS

Including perineal structures in a computational birth model simulation affects the level of stress at the LAM. The maximum stress at the LAM and perineum seems to occur when the head is lower than previously anticipated.

Feasibility and safety of antepartum tactile imaging

Introduction and hypothesis

Quantitative characterization of the birth canal and critical structures before delivery may provide risk assessment for maternal birth injury. The objective of this study was to explore imaging capability of an antepartum tactile imaging (ATI) probe.

Methods

Twenty randomly selected women older than 21 years with completed 35th week of pregnancy and a premise of vaginal delivery were enrolled in the feasibility study. The biomechanical data were acquired using the ATI probe with a double-curved surface, shaped according to the fetal skull and equipped with 168 tactile sensors and an electromagnetic motion tracking sensor. Software package COMSOL Multiphysics was used for finite element modeling. Subjects were asked for assessment of pain and comfort levels experienced during the ATI examination.

Results

All 20 nulliparous women were successfully examined with the ATI. Mean age was 27.8 ± 4.1 years, BMI 30.7 ± 5.8, and week of pregnancy 38.8 ± 1.4. Biomechanical mapping with the ATI allowed real-time observation of the probe location, applied load to the vaginal walls, and a 3D tactile image composition. The nonlinear finite element model describing the stress–strain relationship of the pelvic tissue was developed and used for calculation of Young’s modulus (E). Average perineal elastic modulus was 11.1 ± 4.3 kPa, levator ani 4.8 ± 2.4 kPa, and symphysis–perineum distance was 30.1 ± 6.9 mm. The pain assessment level for the ATI examination was 2.1 ± 0.8 (scale 1–4); the comfort level was 2.05 ± 0.69 (scale 1–3).

Conclusions

The antepartum examination with the ATI probe allowed measurement of the tissue elasticity and anatomical distances. The pain level was low and the comfort level was comparable with manual palpation.

The histological microstructure and in vitro mechanical properties of pregnant and postmenopausal ewe perineal body

OBJECTIVE

The mechanical properties and microstructure of the perineal body are important for the improvement of numerical models of pelvic organs. We determined the mechanical parameters and volume fractions of the ewe perineal body as an animal model.

METHODS

The 39 specimens of 13 pregnant swifter ewes delivering by cesarean section (aged 2 years, weight 61.2 ± 6.2 kg (mean ± standard deviation) and 24 specimens of 8 postmenopausal swifter ewes 150 days after surgical ovariectomy (aged 7 years, 58.6 ± 4.6 kg)) were loaded uniaxially to determine Young's moduli of elasticity in the small (E0) and large (E1) deformation regions, and ultimate stresses and strains. The 63 adjacent tissue samples were processed histologically to assess volume fractions of smooth and skeletal muscle, adipose cells, elastin, and type I collagen using a stereological point testing grid. We compared the structural and mechanical differences along the ewe perineal body, and between pregnant and postmenopausal groups.

RESULTS

The pregnant/postmenopausal perineal body was composed of smooth muscle (12/14%; median), skeletal muscle (12/16%), collagen (10/23%), elastin (8/7%), and adipose cells (6/6%). The E0 was 37/11 kPa (median), E1 was 0.97/1.04 MPa, ultimate stress was 0.55/0.59 MPa, and ultimate strain was 0.90/0.87 for pregnant/postmenopausal perineal body. The perineal body showed a structural and mechanical stability across the sites. The pregnant ewes had a higher amount of skeletal muscle, higher E0, and a less amount of collagen when compared with postmenopausal ewes.

CONCLUSIONS

The data can be used as input for models simulating vaginal delivery, pelvic floor prolapsed, or dysfunction.

Metrics of perineal support (MOPS) study

BACKGROUND

Manual perineal protection (MPP) is an intrapartum intervention suggested to protect perineal integrity during childbirth. Proper execution of MPP is complex and evaluation of its true contribution is difficult in the clinical setting because of the large number of obstetric variables, some of which are hardly quantifiable. In this study we aimed to gather initial data on the forces executed by the accoucheur's thumb, index and middle fingers during MPP at the time of fetal head expulsion, quantify the duration of the intervention and investigate the timely interaction of the different components of MPP.

METHODS

Two bespoke right-handed measurement gloves (MG), with built in sensors, were designed and produced. The MG allowed the electronic real-time measurement of applied forces during MPP and transferred this data wirelessly to an integrated computer system. Sterile gloves were worn over the MG when used at the time of birth. The study was undertaken between January and December 2019. Singleton, term pregnant women having their first vaginal birth who provided a valid written consent were enrolled into this prospective pilot study. All deliveries were undertaken by one of two obstetricians experienced in MPP.

RESULTS

Twenty women were enrolled. The mean duration of execution of MPP during the last contraction was 13.6 s. In 20% it lasted < 5 s. The overall mean values of the average and maximum forces of the thumb, index and middle fingers were 26.7 N; 25.5 N; 20.2 N and 34.3 N; 32.6 N; and 27.6 N respectively. The onset of fingers and thumb activity was simultaneous in 13 cases (65%), while in seven (35%) deliveries the middle finger's force activity was initiated later.

CONCLUSIONS

MPP during fetal head expulsion happens over a short period of time. In the majority of cases the thumb and fingers actions started simultaneously. There were differences in the duration of application and the forces executed by the fingers and thumb between the two practitioners, however this was only significant for thumb measurements. The results obtained will aid in improving further MPP modeling studies to optimize the technique.

Urinary incontinence and its relation to delivery circumstances: A population-based study from rural Kilimanjaro, Tanzania

OBJECTIVES

To investigate the prevalence and risk factors of urinary incontinence (UI), the different UI subtypes and the association between UI and delivery circumstances.

DESIGN

Cross-sectional population-based study conducted in Kilimanjaro Region, Tanzania.

PARTICIPANTS AND SETTINGS

1048 women aged 18-90 women living in rural Kilimanjaro. Simple random sampling was done to select villages, households and participants. Community health workers helped in identifying eligible women and trained nurses/midwives conducted face-to-face interviews. Data were analysed using descriptive statistics and Univariate and Multivariate logistic regression modelling.

RESULTS

The overall prevalence rate of UI was 42%. When focusing on the different types of UI, 17% of the women had stress UI, 9% had urge UI and 16% had mixed UI. Only one woman (0.1%) with vesico-vaginal fistula was identified. UI was found to be significantly associated with increasing parity (OR = 2.41 (1.55-3.74). In addition, women who in relation to their first delivery had delivered at home or had been in labour for more than 24 hours, had increased adjusted ORs of 1.70(1.08-2.68) and 2.10(1.08-4.10), respectively, for having UI.

CONCLUSION

UI is common in rural Tanzania and of the subtypes of UI, Stress Urinary Incontinence (SUI) is the commonest followed by Mixed Urinary Incontinence (MUI). Home delivery, prolonged labour and increasing parity especially having 5 or more deliveries are associated with increased risk for developing UI.

[Childbirth pelvic floor trauma: Anatomy, physiology, pathophysiology and special situations - CNGOF perineal prevention and protection in obstetrics guidelines]

OBJECTIVES

To assess whether pelvic size and shape, spinal curvature, perineal body length and genital hiatus size are associated with the incidence of childbirth pelvic floor trauma. Special situations, such as obesity, ethnicity and hyperlaxity, will also be studied.

METHODS

A bibliographic research using Pubmed and Cochrane Library databases was conducted until May 2018. Publications in English and French were selected by initial reading of the abstracts. Randomized trials, meta-analyzes, case-control studies and large cohorts were studied in a privileged way.

RESULTS

A pubic arch angle<90° (measured clinically) does not appear to increase the risk of OASIS (Level 3), but appears to be a risk factor for postnatal anal incontinence at short-term, but not at long-term (Level 3). Measurement of pelvic dimensions and the subpubic angle is not recommended to predict OASIS or to choose the mode of delivery for the purpose of protecting the perineum (GradeC). Prenatal measurement of both perineal body (Level 3) and genital hiatus (Level 2) does not predict the incidence of 2nd or 3rd degree OASIS. Therefore, the routine prenatal measurement of the length of the perineal body or the genital hiatus is not recommended for any objective related to perineal protection (Grade C). Levator avulsion, resulting in a widening of the genital hiatus, is potentially a source of long-term pelvic floor dysfunction. Biomechanical models suggest that performing a mediolateral episiotomy and applying the fingers to the posterior perineum at the time of expulsive phase may reduce pelvic floor trauma. Obese women have a longer perineal body (Level 3), and obesity does not seem to increase the risk of OASIS (Level 2). There is no difference between Asian and non-Asian women perineal body (Level 3). No studies have validated that the liberal practice of episiotomy in Asian women reduced the risk of OASIS. It is therefore not recommended to practice an episiotomy for simple ethnic reasons in Asian women (GradeC). Compared to white women, black women do not appear to have an increased risk of OASIS and even appear to have a decreased risk of perineal tears of all stages (Level 2). Ligament hyperlaxity seems to be associated with an increased risk of OASIS (Level 2).

CONCLUSIONS

Prenatal assessment of pelvis bone, spine curvature, perineal body and genital hiatus do not allow to predict the incidence of childbirth pelvic floor trauma. Obesity and ethnicity are not risk factors for OASIS.

[Fetal expulsion: Which interventions for perineal prevention? CNGOF Perineal Prevention and Protection in Obstetrics Guidelines]

OBJECTIVE

The objective for all obstetricians and midwifes who intervene during the release of the fetal presentation is to prevent at best the perineal lesions. This work consisted in analyzing the literature, researching and evaluating interventions that reduce this perineal risk during the release.

METHODS

A keyword search for each medical intervention during the expulsion phase was conducted by selecting studies assessing perineal risk. Interventions during pregnancy and during delivery before the expulsion phase were specifically addressed in other sections of the recommendations.

RESULTS

Firstly, the degree of perineal stretching during the second stage of labour does not appear to be a risk factor for OASIS, postpartum incontinence, or sexual disorders (LE3) and that a substantial stretching of the perineum is not an indication of episiotomy (Professional consensus). Then, manual control of the expulsion of the fetus at the end of the second stage of labour and support of the posterior perineum during this time appear to reduce the rate of OASIS (LE3). The crowning of the baby's head should be manually controlled and the posterior perineum manually supported manually to reduce the risk of OASIS (GradeC). There is no recognised benefit to episiotomy in normal deliveries (LE1); the liberal practice of episiotomy results in fewer intact perineums than its restrictive practice, and the latter does not result in increasing the number of cases of OASIS. No evidence indicates that an episiotomy for women with a breech presentation, twin pregnancy, or posterior position prevents OASIS (LE3). Indication for episiotomy during delivery depends on individual risk factors and obstetric conditions (Professional consensus). It is recommended that the indication for episiotomy be explained and the woman's consent received before its performance. The performance of an episiotomy during normal deliveries is not recommended to reduce the risk of OASIS (Grade A). The liberal practice of episiotomy to prevent OASIS is not recommended for women with a breech presentation, twin pregnancy, or posterior position (GradeC). Episiotomy during an instrumental delivery appears to be associated with a reduction of the risk of OASIS (LE3). The vacuum extractor appears to induce fewer cases of OASIS than other instruments (LE3). Episiotomy may be indicated in instrumental deliveries to avoid OASIS (GradeC). Training in perineal protection in obstetrics is recommended (Grade B). In operative vaginal deliveries when several instruments can be used, a vacuum extractor is preferentially recommended to reduce the risk of OASIS (GradeC). When forceps or spatulas are used, it is preferable that they be withdrawn just before cephalic deflexion so that the fetal head is not "capped" with these instruments at birth (Professional consensus). Couder's maneuver, which consists of lowering the forearm during the release of the fetal shoulders, appears to decrease the rate of second-degree perineal tears and increase the rate of intact perineum (LE3).

CONCLUSION

Manual control of the expulsion and perineal support reduce the risk of perineal injury. There is no benefit to episiotomy in normal delivery, nor in special cases such the breech presentation for example. On the other hand, in case of instrumental delivery, an episiotomy may be indicated to avoid OASIS (GradeC), and it is recommended if it is possible to use the ventouse preferentially. The Couder's maneuver seems to reduce the rate of 2^nd degree perineal lesions (LE3). Finally, training in perineal obstetric protection is recommended (Grade B).