*2.2.1 Premature cervical extracellular matrix changes inducing preterm/premature cervical failure*

Cervical stroma ensures mechanical properties [40] by ECM molecules arranged in a scaffold/matrix, and cells. One must understand mathematical models through Humphrey and Rajagopal [41] mixture theory. Updated after 20 years [42] for soft tissue growth [changing mass, solid (cells, fibers), and fluid-interstitial], and remodeling (changing microstructure) for adaption at new growth imposed functions. Microarrays and gene analysis [43] in murine models revealed two distinct phases – softening and ripening. Cervical human transcriptome is mentioned more than a decade ago [44], with some considerations on distinct cervical microRNA profiles in women destined to sPTB [45], cervical softening—an active phase, as shown in nearly daily assessment in murine models [15, 39] with rapid onset after conception, is defined as the first measurable increase in tissue distensibility versus to non-pregnant, with a precisely timed activation of slow molecular, microstructural, and mechanical changes up to term/labor [9], regarding cellularity, collagen, elastin, GAGs, proteoglycans, water. Softening drives alterations in collagen fibers organization and alignment, inducing a distinctive arrangement—short, thick, and curved, with low linearity, and change in the number and type of cross-linking between newly formed fibrils, coinciding with a marked increase in hyaluronic acid (HA), and water uptake, globally reducing mechanical resistance to tension [15, 46], an influx/ activation of immune cells releasing MMPs degrading ECM [37], increase elasticity, and prepare inferior segment for delivery. Collagen waviness confers tissue isotropy and heterogeneity, destabilizing mechanical integrity with great deformations and relaxations and increased compliance necessary for uterine cavity rising pressure, with tissue integrity maintenance. Ripening—a term used first by Winkler and Rath [47]—is near labor onset, with rapid evolution, cervix marked softening and shortening. Preterm and term cervical changes are similar, not identical; sPTB can result from aberrant events timing [4]. Murine studies showed differences in the molecular mechanisms governing preterm and term ripening [38, 48]. Untimely cervical ripening in early gestation—earlier than normal (before 24–36<sup>6</sup> days weeks, in women), predisposes to CI, responsible for recurrent late miscarriage/sPTB, and cervical ripening inadequate in late pregnancy is associated with induction failure/prolonged labor, possible involvement of EMC and CSMCs from IO [30]. Murine preterm-induced delivery showed a dramatic reduction of mature collagen fibers, increased new fibrils synthesis, packing disorganization by the gradual replacement of mature cross-linked collagen with collagen harboring reduced cross-linking, less cross-linking between fibers of new fibrils of tropocollagen, which are shorter and thicker than in non-pregnant, besides the distinctive arrangement of fibers—from being aligned to curling, becoming isotropic [46], greater spaces between fibers, decline in thrombospondin-2 and tenascin-C [36], and ECM high hydration [49], the parallelism between water and hyaluronic acid (HA) with very hydrophilic large molecular weight-hyaluronan, increases wet weight vs*.* controls, and in mice at term [36, 43], affecting collagen organization [50]. The interstitial fluid controls tissue stiffness response, water content increases by 5%, modifying cervix mechanical properties, generating an unbalance/non-equilibrium state [51], and the untimed ripening initiates rapid incremental

#### **Figure 2.**

*Proposed model for mice cervical remodeling for mechanical resistance reduce. A. Increase of high molecular weight (MW) hyaluronan in ECM from early to late pregnancy. B. At pregnancy end, high levels HA and versican form cross-links, which are associated with water uptake, increased tissue compliance, visco-elasticity, and collagen disorganization. C. During labor, enzymes (hyaluronidase and ADAMTS enzymes) cleave HA, and versican, causing cervical tissue integrity and complete loss for dilation. D. During postpartum repair, low MW hyaluronan, versican fragments, and damaged collagen are removed by immune cells—neutrophils and macrophages. Adapted from Timmons et al. [15]. PMC free article. HHS Public access.*

fall in cervical mechanical strength (**Figure 2**) [37]. As in other tissues (cartilage and blood vessels) with complex mechanical behavior, the relative ratio of collagen to proteoglycans is an important determinant of cervix visco-elasticity, compliance, and ultimate function [52].

The first presented 3D anisotropic hyperelastic model [38], based on Langevin statistical mechanics for human and mice gestational mechanical response, revealed: constant total collagen content per volume along pregnancy; mature collagen crosslink disorganization in human ripening cervix evolves by an increase in tissue acid solubility, along pregnancy; mice collagen cross-link disorganization progresses from d6 (when bundles are larger) to d15, with little change after d15. This difference explains mouse cervix resistance to break in uniaxial tensile test compared to human, in non-pregnant and pregnant state.

The stiffness progressive reduction in normal human pregnancies starts from first trimester (>2 vs. non-pregnant). It continues in the second, but not between the second and third trimester, with consistent recovery after delivery, to the level of early pregnancy, as ectocervix aspiration technique depicted [53]. Cervical shortening normally starts from mid-pregnancy and progresses until delivery, as ultrasound longitudinal studies on cervix length (CL) sustain [54], being a normal 30 mm CL at pregnancy beginning, with individual variations, from population, age, parity, and gestational outcomes, as a systematic review, and meta-analysis report [55].

EMC organization and composition aberrant regulation during softening, a tissue property, may contribute to premature shortening—a tissue deformation that results from an evolving 3D stress state, and the intrinsic constituents remodeling [56], softening plus shortening being considered as dysfunctional EMC remodeling [20], and IO "funneling" is next step, due to softness, and sphincterian HCSMCs relaxation

*Abnormal Cervical Remodeling Early Depiction by Ultrasound Elastography: Potential… DOI: http://dx.doi.org/10.5772/intechopen.113314*

[30], added to dysfunctional remodeling that starts invariably from IO [57], where is the higher stress compared to EO. EO is not significantly loaded until the cervix has significantly shortened [58], and 3D hyperelastic anisotropic model, revealed relative similar stress to both orifices, and the middle part is between those in the IO and EO [38].
