The mechanical role of the cervix in pregnancy

Abstract

Appropriate mechanical function of the uterine cervix is critical for maintaining a pregnancy to term so that the fetus can develop fully. At the end of pregnancy, however, the cervix must allow delivery, which requires it to markedly soften, shorten and dilate. There are multiple pathways to spontaneous preterm birth, the leading global cause of death in children less than 5 years old, but all culminate in premature cervical change, because that is the last step in the final common pathway to delivery. The mechanisms underlying premature cervical change in pregnancy are poorly understood, and therefore current clinical protocols to assess preterm birth risk are limited to surrogate markers of mechanical function, such as sonographically measured cervical length. This is what motivates us to study the cervix, for which we propose investigating clinical cervical function in parallel with a quantitative engineering evaluation of its structural function. We aspire to develop a common translational language, as well as generate a rigorous integrated clinical-engineering framework for assessing cervical mechanical function at the cellular to organ level. In this review, we embark on that challenge by describing the current landscape of clinical, biochemical, and engineering concepts associated with the mechanical function of the cervix during pregnancy. Our goal is to use this common platform to inspire novel approaches to delineation of normal and abnormal cervical function in pregnancy.

A continuous fiber distribution material model for human cervical tissue

“…During pregnancy there is a drastic softening that must occur within the cervical tissue to accommodate the delivery of the baby (see cervical mechanics review in this special issue Myers et al, 2015). This softening is accomplished through a complex biochemical cascade of events that remodel the ECM components of the tissue (Read et al, 2007; Word et al, 2007; Holt et al, 2011).…”

“…The in vivo loading conditions of the cervix depend on many interacting geometric and material factors, including anatomical shape, tissue material properties, and contact between the organs. A review of these variables and the current state of pregnancy biomechanics is presented in a companion paper in this special issue (Myers et al, 2015). …”

Simulating uterine contraction by using an electro-chemo-mechanical model

“…Furthermore, the cervical end of the uterus is assumed to be fixed in all directions. In reality the cervix is a compliant structure (Badir et al 2013;Mazza et al 2014;Briggs et al 2015;Myers et al 2015), and a more realistic, but still simple, boundary condition would be to assume a linearly elastic support. Numerical experiments using data from Badir et al (2013, Fig 11) indicate that the IUP remains relatively unchanged by this condition, but unphysiological oscillations in the displacement of the uterine wall led to the conclusion that this approach needs further work.…”

Analysis of the collagen fibers on autopsied patients’ uterus with the Acquired Immunodeficiency Syndrome

“…9 The cervical mechanical activity has two functions: before childbirth, it should remain closed and resist to the mechanical load of the pregnancy and at the moment of childbirth it should be soft to be deformed and dilated allowing a passage for the fetus. 10 The organization of the collagen in the human cervical tissue plays an important role in the structural function of the tissue. 11 The cervical collagen is like fibers in a hierarchical network embedded in a superficial viscous substance of glycosaminoglycans negatively charged and other proteins.…”

“…11 The cervical collagen is like fibers in a hierarchical network embedded in a superficial viscous substance of glycosaminoglycans negatively charged and other proteins. 10 The collagen (types I and III) compose of 34 to 77% of dry weight, 12,13 with evidence in studies on human tissues that this dry weight content remains constantly during the gestation. 14 In general, the collagen fiber network is reported to be anisotropic with different orientations in distinct anatomical regions within the cervix.…”