The Effect of Pregnancy and Postpartum Recovery on the Viscoelastic Behavior of the Rat Cervix

Abstract

The objective of this study was to elucidate the normal functional adaptations of the cervix in pregnancy. Utilizing a Long-Evans rodent model, the cervix was divided into distal and proximal portions for virgin, mid-pregnant, and four weeks postpartum animals. The quasi-linear viscoelastic theory describes the elastic and viscous behavior of the cervix. A hydroxyproline assay was used to measure collagen content. The nonlinearity of the elastic response significantly increased throughout the entire cervix during pregnancy when compared to virgin samples (p < 0.05) and was similar to virgin samples postpartum. All viscous behavior, except for the short-term relaxation of the proximal cervix, significantly differed for pregnant specimens (p < 0.05) and remained similar to pregnant samples postpartum. Collagen content was found to increase by mid-pregnancy only in the proximal cervix when compared to virgin. Distal and proximal portions, however, were found to differ in collagen content at all time points (p < 0.05). This study finds that the cervix becomes elastically stiffer with increasing strain and exhibits increased viscous behavior during pregnancy, with incomplete recovery postpartum. These alterations allow for quick dissipation of loads, and are likely related to altered matrix organization and porosity reported by others.

Mechanical Properties of Female Reproductive Organs and Supporting Connective Tissues: A Review of the Current State of Knowledge

“…5 Animal models used to collected mechanical data on pelvic tissues. Monkeys were used for the vagina and pelvic ligaments [94], swine for the uterus [27] and pelvic ligaments [87,96,97], ewes for the vagina [65,80], and rats/mice for the cervix [44][45][46], vagina [59,64], uterus [25], and pelvic ligaments [93]. muscle, etc.)…”

“…[40,44,45] and traditional test [36]) and compression (confined [40,46] and unconfined [36,40]). These tests were performed on rat tissue [44][45][46] as well as on human tissue [36,40] using load-relaxation protocols. The tissues in both tension and compression tests for all the obstetric conditions that were considered displayed a nonlinear stress-strain response.…”

Hyperelastic Ex Vivo Cervical Tissue Mechanical Characterization

“…Many authors have modeled the behaviour of soft tissues such as, porcine spleen, porcine kidney, porcine liver, rat or human brain [18][19][20][21][22]. Regarding cervical tissue, uniaxial tension tests [23][24][25][26][27] and compression [25,28,29] have been studied in rat tissue and human tissue using load-relaxation protocols. A nonlinear stress-strain response has been shown in the tension and compression tests and the response of the tissue was noticeably stiffer in tension than in compression.…”

The mechanical response of the mouse cervix to tensile cyclic loading in term and preterm pregnancy

“…Microscopic imaging of the collagen network during pregnancy reveal a dynamic remodeling from straight fibers for non-pregnant tissue to thicker, crimped fibers for pregnant tissues [21, 22], in both human and mouse cervices. Cervical collagen also undergoes a turnover during pregnancy where mature cross-linked collagen is progressively replaced by immature less cross-linked collagen [17] while total collagen content remains the same [23, 14]. …”