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Pregnant anatomy. Representative illustration of a sagittal view of pregnant anatomy with relevant reproductive and surrounding structures labeled. Asterisks ( � ) indicate structures evaluated in the protocol. https://doi.org/10.1371/journal.pone.0242118.g001
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Tissue mechanics is central to pregnancy, during which maternal anatomic structures undergo continuous remodeling to serve a dual function to first protect the fetus in utero while it develops and then facilitate its passage out. In this study of normal pregnancy using biomechanical solid modeling, we used standard clinical ultrasound images to obt...
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Context 1
... mechanical integrity and function of reproductive tissues is clearly critical to pregnancy outcome [2][3][4][5]. The uterus, fetal membranes, and cervix each have dynamic, biological, and mechanical roles (Fig 1); these tissues must remodel and stretch to accommodate the growing fetus while it develops in utero, and then do the opposite, i.e. contract, deform, or rupture, to facilitate safe delivery of the fetus. Failure and mistiming of these essentially mechanical events contribute to major obstetrical complications such as PTB [6,7]. ...
Citations
... accomplish the objectives of this work, following the instructions of Louwagie et al. (Louwagie et al. 2021). Since the geometric model is parametrized, it is possible to generate patient-specific geometries by changing the required dimensions. ...
... Since the geometric model is parametrized, it is possible to generate patient-specific geometries by changing the required dimensions. The model was developed for a mid-thirdtrimester gravid uterine body and cervix, using the average dimensions from different patients retrieved from Louwagie et al. (Louwagie et al. 2021 ...
... Regarding the initial cervical shape (i), three scenarios were considered (Louwagie et al. 2021): ...
Successful pregnancy highly depends on the complex interaction between the uterine body, cervix, and fetal membrane. This interaction is synchronized, usually following a specific sequence in normal vaginal deliveries: (1) cervical ripening, (2) uterine contractions, and (3) rupture of fetal membrane. The complex interaction between the cervix, fetal membrane, and uterine contractions before the onset of labor is investigated using a complete third-trimester gravid model of the uterus, cervix, fetal membrane, and abdomen. Through a series of numerical simulations, we investigate the mechanical impact of (i) initial cervical shape, (ii) cervical stiffness, (iii) cervical contractions, and (iv) intrauterine pressure. The findings of this work reveal several key observations: (i) maximum principal stress values in the cervix decrease in more dilated, shorter, and softer cervices; (ii) reduced cervical stiffness produces increased cervical dilation, larger cervical opening, and decreased cervical length; (iii) the initial cervical shape impacts final cervical dimensions; (iv) cervical contractions increase the maximum principal stress values and change the stress distributions; (v) cervical contractions potentiate cervical shortening and dilation; (vi) larger intrauterine pressure (IUP) causes considerably larger stress values and cervical opening, larger dilation, and smaller cervical length; and (vii) the biaxial strength of the fetal membrane is only surpassed in the cases of the (1) shortest and most dilated initial cervical geometry and (2) larger IUP.
... Globally, more than 1 in 10 babies is 18 born preterm, and PTB-related complications are the leading cause of death for children 19 under 5 years of age [5]. Cited causes of PTB with biomechanical implications are 20 uterine overdistention, preterm premature rupture of membranes, and cervical 21 insufficiency [6]. Still, the pathophysiology and interplay of these conditions remain 22 unknown, and 70-80% of PTB is spontaneous and unexplained [6,7]. ...
... The cervix is the most scrutinized 54 of the maternal anatomic features during pregnancy, as cervical length can be used as a 55 predictive tool for PTB, and time-course studies of cervical length and stiffness have 56 been reported [18,19]. In 2021, our team published the first datasets on uterine and 57 cervical dimension measurements, cervical stiffness data, and computer-aided design 58 (CAD) models of the uterus and cervix across gestation in 29 uncomplicated 59 pregnancies, making all data and models publicly available to create wider opportunity 60 for in-silico pregnancy research [20,21]. ...
... In this study, we build upon previous work to quantify anatomical and 62 biomechanical changes in the uterus and cervix across gestation in pregnant participants 63 at low-risk for preterm birth. Our approach is to parametrically assess the size and 64 shape of the uterus and cervix through a clinically implementable two-dimensional (2D) 65 ultrasound protocol and measure in-vivo cervical stiffness via aspiration [20,22]. ...
The coordinated biomechanical performance, such as uterine stretch and cervical barrier function, within maternal reproductive tissues facilitates healthy human pregnancy and birth. Quantifying normal biomechanical function and detecting potentially detrimental biomechanical dysfunction (e.g., cervical insufficiency, uterine overdistention, premature rupture of membranes) is difficult, largely due to minimal data on the shape and size of maternal anatomy and material properties of tissue across gestation. This study quantitates key structural features of human pregnancy to fill this knowledge gap and facilitate three-dimensional modeling for biomechanical pregnancy simulations to deeply explore pregnancy and childbirth. These measurements include the longitudinal assessment of uterine and cervical dimensions, fetal weight, and cervical stiffness in 47 low-risk pregnancies at four time points during gestation (late first, middle second, late second, and middle third trimesters). The uterine and cervical size were measured via 2-dimensional ultrasound, and cervical stiffness was measured via cervical aspiration. Trends in uterine and cervical measurements were assessed as time-course slopes across pregnancy and between gestational time points, accounting for specific participants. Patient-specific computational solid models of the uterus and cervix, generated from the ultrasonic measurements, were used to estimate deformed uterocervical volume. Results show that for this low-risk cohort, the uterus grows fastest in the inferior-superior direction from the late first to middle second trimester and fastest in the anterior-posterior and left-right direction between the middle and late second trimester. Contemporaneously, the cervix softens and shortens. It softens fastest from the late first to the middle second trimester and shortens fastest between the late second and middle third trimester. Alongside the fetal weight estimated from ultrasonic measurements, this work presents holistic maternal and fetal patient-specific biomechanical measurements across gestation.
... The shape of the inflated balloon also changes based on the "L" value: it tends to become closer to a sphere (when inflated in the open air) the more we increase "L". 34 , we adopted an intermediate value for "L". Based on this final choice, the black signs shown in Fig. 1a were applied to the rectal probe. ...
The 3.1 target of the Sustainable Development Goals of the United Nations aims to reduce the global maternal mortality ratio to less than 70 maternal deaths per 100,000 live births by 2030. The last updates on this target show a significant stagnation in the data, thus reducing the chance of meeting it. What makes this negative result even more serious is that these maternal deaths could be avoided through prevention and the wider use of pharmacological strategies and devices to stop postpartum haemorrhage (PPH). PPH is the leading obstetric cause of maternal mortality in low- and middle-income countries (LMICs). Despite low-cost devices based on the uterine balloon tamponade (UBT) technique are already available, they are not safe enough to guarantee the complete stop of the bleeding. When effective, they are too expensive, especially for LMICs. To address this issue, this study presents the design, mechanical characterisation and technology assessment performed to validate a novel low-cost UBT kit, particularly a novel component, i.e., the connector, which guarantees the kit’s effectiveness and represents the main novelty. Results proved the device’s effectiveness in stopping PPH in a simulated scenario. Moreover, economic and manufacturing evaluations demonstrated its potential to be adopted in LMICs.
... Fiber distribution characterizes the capability of the cervix to resist to both dilatative and compressive forces [6]. During pregnancy, specific areas, such as the internal cervical os and possibly the upper posterior cervix, receive [8,9] and counteract [5,9] the fetus's tensile and dilatative forces. Collagen fibers play an essential role in maintaining cervix competence, and when they decrease and disperse, cervix dilation may occur [2,5,10]. ...
... Fiber distribution characterizes the capability of the cervix to resist to both dilatative and compressive forces [6]. During pregnancy, specific areas, such as the internal cervical os and possibly the upper posterior cervix, receive [8,9] and counteract [5,9] the fetus's tensile and dilatative forces. Collagen fibers play an essential role in maintaining cervix competence, and when they decrease and disperse, cervix dilation may occur [2,5,10]. ...
... Published investigations on cervix structure based on histology, imaging techniques, and mathematical models never considered the position of the uterus as a confounding factor [1][2][3][4][5][6][7][8][9][10]. Future studies need to incorporate the angle of flexion of the uterus among the variables that may influence the results. The possible implications of a different composition of the cervix linked to the angle of flexion should be considered in association with different obstetrics and gynecological disturbances and pathologies. ...
Strain elastography allows the evaluation of tissue elasticity. Background/Objectives: Tissue elasticity depends on the content and distribution of collagen fibers and is shaped by the applied tensile forces that may differ in uteri with a different angle of flexion of the corpus on the cervix. The objective was to investigate whether the angle of uterine flexion is related to cervical tissue elasticity. Methods: The anterior angle between the longitudinal axis of the uterus corpus and that of the cervix was measured in 275 non-pregnant young women by transvaginal ultrasonography and considered both as an absolute value or categorized as ≤150°, between >150° and ≤210°, and >210°. Strain elastography was used to assess tissue elasticity by placing the probe in the anterior vaginal fornix. Tissue elasticity was evaluated in the middle of the anterior cervical compartment (ACC), in the middle of the posterior cervical compartment (PCC), in the middle portion of the cervical canal (MCC), and at the internal cervical os (ICO). In a sagittal plane MCC was evaluated across the cervical canal, and ACC and PCC at a distance equal between the cervical canal and the outer anterior or posterior part of the cervix. MCC, ACC and PCC were evaluated at equal distance between the ICO and the external cervical os. Elasticity was expressed as a color score ranging from 0.1 (low elasticity) to 3 (high elasticity). Results: The angle of uterine flexion show a negative linear relation with the elasticity of the ACC (p = 0.001) and MCC (p = 0.002) and a positive relation with the elasticity of the PCC (p = 0.054). In comparison to uteri with an angle of flexion of <150°, those with an angle of flexion of >210° had lower elasticity of the ACC (p = 0.001) and MCC (p = 0.001) and higher elasticity of the PCC (p = 0.004). The ACC/PCC and PCC/MCC elasticity ratios were also significantly different (p = 0.001). Conclusions: The angle of uterine flexion is associated with changes in cervix elasticity. Retroflexion is associated with stiffer ACC and MCC and a more elastic PCC. Differences in tissue elasticity suggest structural changes of the cervix that may have implication in variate obstetric and gynecological conditions.
... Nos últimos anos, observa-se o aumento do uso de modelos computacionais para estudos relacionados à gravidez e saúde da mulher, tais como o estudo de contrações uterinas a termo (Cochran et al., 2015;Sharifimajd et al., 2016), a biomecânica do parto normal (Vila Pouca et al., 2019), o desenvolvimento de modelos paramétricos de úteros gravídicos (Louwagie et al., 2021), a lesão da musculatura do assoalho pélvico devido ao acúmulo de microdanos (Vila Pouca et al., 2022), a função mecânica do colo do útero durante a gravidez (Shi et al., 2022), entre outros. ...
O parto prematuro, grave problema de saúde pública, afeta um em cada dez bebês globalmente. A distensão patológica do útero pode impor uma tensão à parede uterina capaz de desencadear contrações e, assim, levar ao parto prematuro. Apesar do crescente uso de modelos computacionais para estudos relacionados à gravidez, a falta de dados experimentais e questões éticas limitam os estudos sobre as propriedades mecânicas do útero durante a gestação. Este trabalho apresenta um estudo computacional do crescimento uterino durante a segunda metade da gestação. O modelo geométrico representa o corpo uterino e foi obtido a partir de elipsóides truncados. O modelo constitutivo utilizado é anisotrópico e o tecido foi considerado incompressível. Nessa abordagem, a simulação foi realizada aplicando uma pressão intrauterina e condições de contorno simplificadas. Os resultados obtidos nas simulações mostram a evolução e deformação do útero com o aumento da pressão intrauterina.
... Parametric Geometries A baseline representative model of a uterus and cervix was generated by averaging patient uterine dimensions acquired from MRI images of five at-term pregnant patients and constructing a geometry in Solidworks 2022 (Dassault Systémes, France) as previously described [15][16][17]. A scar (Fig. 1A) and surrounding abdomen tissue were also included in the Solidworks model [18]. ...
Uterine rupture is an intrinsically biomechanical process associated with high maternal and fetal mortality. A previous Cesarean section (C-section) is the main risk factor for uterine rupture in a subsequent pregnancy due to tissue failure at the scar region. Finite element modeling of the uterus and scar tissue presents a promising method to further understand and predict uterine ruptures. Using patient dimensions of an at-term uterus, a C-section scar was modeled with an applied intrauterine pressure to study how scars affect uterine stress. The scar positioning and uterine thickness were varied, and a thickness defect was incorporated into the scar region. The modeled stress distributions confirmed clinical observations as the increased regions of stress due to scar positioning, thinning of the uterine walls, and the presence of a defect are consistent with clinical observations of features that increase the risk of uterine rupture.
... In this study, both anterior and posterior cervical lips remained softer in the cervical insufficiency group during the second trimester, whereas only the anterior cervical lip was softer in the first trimester in our previous study [10]. Louwagie et al. demonstrated that the anterior uterocervical angle shifts posteriorly throughout gestation using biomechanical solid modeling [17]. Multiple factors contribute to cervical softening, including progressive changes in cervical tissue hydration, collagen structure and tissue elasticity [18]. ...
Background
We previously demonstrated that pregnant women with a history of cervical insufficiency had a softer anterior cervical lip, shorter cervical length and wider endocervical canal in the first trimester. The aim of this study was to investigate changes in cervical elastography, cervical length, and endocervical canal width in the second trimester after cerclage, and further discuss whether these ultrasound parameters are predictive of preterm delivery.
Methods
This was a secondary analysis of cervical changes in singleton pregnancies after cerclage from January 2016 to June 2018. Cervical elastography, cervical length, and endocervical canal width were measured during the second trimester in the cervical insufficiency group and control group without cervical insufficiency. Strain elastography under transvaginal ultrasound was used to assess cervical stiffness and presented as percentage (strain rate).
Results
Among the 339 pregnant women enrolled, 24 had a history of cervical insufficiency and underwent cerclage. Both anterior and posterior cervical lips were significantly softer in the cervical insufficiency group even though they received cerclage (anterior strain rate: 0.18 ± 0.06% vs. 0.13 ± 0.04%; P = 0.001; posterior strain rate: 0.11 ± 0.03% vs. 0.09 ± 0.04%; P = 0.017). Cervical length was also shorter in the cervical insufficiency group (36.3 ± 3.6 mm vs. 38.3 ± 4.6 mm; P = 0.047). However, there was no significant difference in endocervical canal width between the two groups (5.4 ± 0.7 mm vs. 5.6 ± 0.7 mm; P = 0.159). Multivariate logistic regression analysis also revealed significant differences in anterior cervical lip strain rate (adjusted odds ratio [OR], 7.32, 95% confidence interval [CI], 1.70-31.41; P = 0.007), posterior cervical lip strain rate (adjusted OR, 5.22, 95% CI, 1.42–19.18; P = 0.013), and cervical length (adjusted OR, 3.17, 95% CI,1.08–9.29; P = 0.035). Among the four ultrasound parameters, softer anterior cervical lip ( P = 0.024) and shorter cervical length ( P < 0.001) were significantly related to preterm delivery.
Conclusions
Cervical cerclage can prevent widening of the endocervical canal, but not improve cervical elasticity or cervical length. Measuring anterior cervical elastography and cervical length may be valuable to predict preterm delivery.
... The solid component of the tissue is composed mainly of types 1 and 3 fibrous collagen, elastic fibers, proteoglycans, and glycosaminoglycans . The nulliparous, nonpregnant, human cervix is about 3-4 cm long and 2.5-3 cm in diameter -although its size and shape vary significantly among patients Louwagie et al., 2021). The location of the squamocolumnar junction relative to the external os is dynamic throughout a patient's lifetime as the cervix grows and shrinks. ...
... Generally, parous patients have larger cervixes than nulliparous patients, and premenopausal patients have larger cervixes than postmenopausal patients (Prendiville and Sankaranarayanan, 2017). During pregnancy, the cervical length slightly decreases while the outer diameter of the cervix increases (Louwagie et al., 2021). ...
... Finally, bioengineers use finite element modeling to understand how material property changes affect cervical dilation (Mahmoud et al., 2013;. In these models, constitutive relationships are applied to isolated cervical geometry (Gou et al., 2020) or patient-derived anatomies that include the uterus and cervix from imaging data, such as MRI or ultrasound (Louwagie et al., 2021;. Continued developments with these techniques have the exciting potential to incorporate patient-specific anatomical and mechanical changes (informed by the in vivo tools outlined previously) to predict the trajectory and timing of cervical dilation during pregnancy. ...
The uterine cervix plays two important but opposing roles during pregnancy – as a mechanical barrier that maintains the fetus for nine months and as a compliant structure that dilates to allow for the delivery of a baby. In some pregnancies, however, the cervix softens and dilates prematurely, leading to preterm birth. Bioengineers have addressed and continue to address the lack of reduction in preterm birth rates by developing novel technologies to diagnose, prevent, and understand premature cervical remodeling. This article highlights these existing and emerging technologies and concludes with open areas of research related to the cervix and preterm birth that bioengineers are currently well-positioned to address.
... 40 The CL change was also discovered during gestation; the CL in nullipara decreased during gestation, in which the CL in multipara stayed relatively constant. 41 The CL tends to increase over age in nonpregnant nullipara. 40 Regarding the cervical orifice, pregnant women tend to have wider cervical orifice than nonpregnant women. ...
Introduction:
Pap smear training is commonly conducted using simulators before practicing with humans. Unfortunately, existing simulators do not well simulate the biomechanical properties of pelvic tissues, and this may negatively impact the training outcome. In this study, we used finite element analysis (FEA) to identify a material that most accurately simulates pelvic tissues in terms of biomechanical properties for fabricating gynecologic training simulators. The selected material was then used to fabricate a vagina and cervix model using a hybrid technique of fused deposition modeling and molding to qualitatively confirm the structural integrity of the simulator.
Methods:
The vagina and cervix were reconstructed in a 3-dimensional feature according to geometrical parameters reported in the literature. The biomechanical compliance of the simulators was investigated by comparing 5 materials-RTV615, Dragon Skin 10, Dragon Skin 30, Dragon Skin FX-Pro, and Ecoflex 00-30-and a pelvic tissue model (control) using 2 FEA modules. The structural mechanics module simulated the insertion and opening of a vaginal speculum, and the (1) horizontal opening of the vagina and peak von Mises stress at the anterior and (2) posterior walls of the vagina were obtained. The explicit dynamics module estimated (1) the fracture stress during punch biopsies and (2) maximum perpendicular deformation of the cervix before break. The most biomechanically compliant material was subsequently used to fabricate the simulator using the hybrid technique.
Results:
From the FEA, the horizontal opening of the vagina, peak von Mises stress at the anterior wall of the vagina, peak von Mises stress at the posterior wall of the vagina fracture stress, and maximum perpendicular deformation of the cervix before break were obtained; the results of Dragon Skin 10 and the control were most similar. Therefore, the simulator was fabricated using the material. A qualitative evaluation of the simulator by the naked eye verified its structural integrity.
Conclusions:
Of the materials studied, the FEA results showed that Dragon Skin 10 was the most accurate material for simulating pelvic tissues in terms of the biomechanical properties in a gynecologic training simulator. The simulator was also successfully fabricated using the hybrid technique. Further studies may also involve experimental testing to support the simulation results.
... The first requirement is to reproduce the actual size and shape of the uterus at the time of delivery. Data were taken from a study on two-dimensional ultrasound images of the uterus and cervix in pregnant subjects (Louwagie et al., 2021). However, it is worth pointing out that during pregnancy, the uterine tissue easily adapts to the size of the foetus and can quickly recover its size after delivery, thanks to the contraction process that follows the birth. ...
... The uterine body was designed by referring to data taken from two studies. In Louwagie et al. (2021), several measurements of the structural dimensions of the gravid uterus and cervix during gestation are available, while in Paliulyte et al. (2017), fewer parameters (uterine size in the three directions) are provided. The phantom was created using Autodesk Inventor V R . ...
Purpose
The purpose of this study is to describe the design and validation of a three-dimensional (3D)-printed phantom of a uterus to support the development of uterine balloon tamponade devices conceived to stop post-partum haemorrhages (PPHs).
Design/methodology/approach
The phantom 3D model is generated by analysing the main requirements for validating uterine balloon tamponade devices. A modular approach is implemented to guarantee that the phantom allows testing these devices under multiple working conditions. Once finalised the design, the phantom effectiveness is validated experimentally.
Findings
The modular phantom allows performing the required measurements for testing the performance of devices designed to stop PPH.
Social implications
PPH is the leading obstetric cause of maternal death worldwide, mainly in low- and middle-income countries. The proposed phantom could speed up and optimise the design and validation of devices for PPH treatment, reducing the maternal mortality ratio.
Originality/value
To the best of the authors’ knowledge, the 3D-printed phantom represents the first example of a modular, flexible and transparent uterus model. It can be used to validate and perform usability tests of medical devices.
