System-Level Biomechanical Approach for the Evaluation of Term and Preterm Pregnancy Maintenance

Abstract

Preterm birth is the primary contributor to perinatal morbidity and mortality, with those born prior to 32 weeks disproportionately contributing compared to those born at 32-37 weeks. Outcomes for babies born prematurely can be devastating. Parturition is recognized as a mechanical process that involves the two processes that are required to initiate labor: rhythmic myometrial contractions and cervical remodeling with subsequent dilation. Studies of parturition tend to separate these two processes rather than evaluate them as a unified system. The mechanical property characterization of the cervix has been primarily performed on isolated cervical tissue, with an implied understanding of the contribution from the uterine corpus. Few studies have evaluated the function of the uterine corpus in the absence of myometrial contractions or in relationship to retaining the fetus. Therefore, the cervical-uterine interaction has largely been neglected in the literature. We suggest that a system-level biomechanical approach is needed to understand pregnancy maintenance. To that end, this paper has two main goals. One goal is to highlight the gaps in current knowledge that need to be addressed in order to develop any comprehensive and clinically relevant models of the system. The second goal is to illustrate the utility of finite element models in understanding pregnancy maintenance of the cervical-uterine system. The paper targets an audience that includes the reproductive biologist/clinician and the engineer/physical scientist interested in biomechanics and the system level behavior of tissues.

The mechanical role of the cervix in pregnancy

“…Insight into the physiologic loads experienced during pregnancy and the load-carrying capability of the cervix have been derived from finite element models (Fernandez et al, 2015; House et al, 2012, 2013; Mahmoud et al, 2013; Paskaleva, 2007), mechanical and biochemical studies of ex vivo tissue specimens (Conrad et al, 1980; Conrad and Ueland, 1976, 1979; Fernandez et al, 2013; Gan et al, 2014; Myers et al, 2008, 2010; Oxlund et al, 2010a,b; Petersen et al, 1991; Rechberger et al, 1988; Yao et al, 2014), in vivo mechanical and biochemical interrogations of the cervix (Badir et al, 2013a; Bauer et al, 2007; Feltovich et al, 2010, 2012; Feltovich and Hall, 2013; Hee et al, 2014; House et al, 2005, 2009; Hricak et al, 1990; Maldjian et al, 1999; Mazza et al, 2006, 2013; Parra-Saavedra et al, 2011), and theoretical mechanics (Liao et al, 2014; Myers and Ateshian, 2014; Paskaleva, 2007). At the present time, there is no single set of correlating geometric and material property data from a single pregnant patient throughout gestation.…”

Investigating the mechanical function of the cervix during pregnancy using finite element models derived from high-resolution 3D MRI

“…Those factors make it difficult to discern the detailed mechanical stress state of the organs. Previous studies have investigated the mechanical loading state of the cervix through finite element models with CAD-based (House and Socrate 2006; House, Feltovich, et al 2012; Paskaleva 2007) and 2D (Mahmoud, Wagoner Johnson, et al 2013) geometry measured from medical images. Our study builds upon past knowledge using anatomy-based models with fewer simplifying geometric assumptions.…”

A continuous fiber distribution material model for human cervical tissue

“…The in vivo 3-dimensional (3D) deformation and stress state of the cervix during pregnancy is complex due to patient-specific pelvic geometry, pelvic tissue material properties, passive and active external loading, and the contact and boundary conditions between organs (House et al, 2009, 2012, 2013; Mahmoud et al, 2013; Fernandez et al, 2015). The stress state of the cervix has been studied using CAD-based (House et al, 2012; Mahmoud et al, 2013) and patient-specific MRI-based (Fernandez et al, 2015) finite element models of the pregnant pelvis.…”

“…The stress state of the cervix has been studied using CAD-based (House et al, 2012; Mahmoud et al, 2013) and patient-specific MRI-based (Fernandez et al, 2015) finite element models of the pregnant pelvis. Simulation results reveal that under a constant intrauterine pressure the stress state of the cervix is a combination of tension and compression (Fig.…”