BRITE Pivot: Using Fracture Mechanics to Study Childbirth after an Episiotomy

An episiotomy, in which a doctor or midwife makes a small incision from the back of the vagina through the perineum towards the anus to widen the vaginal opening, is sometimes used during childbirth to create more room for the fetus to be extracted. However, an episiotomy also creates very high internal stresses in the perineum at the tip of the incision. The objective of this work is to calculate the stress at the tip of the episiotomy under a wide range of conditions, including the geometry and length of the incision, the size of the fetal head, and the properties of the muscle and tissue of the pelvic floor, and determine when an episiotomy will lead to further tearing of the perineum during childbirth. As such, this work will help guide when an episiotomy should be performed and establish the type and length of episiotomy to use to lessen the risk of additional tearing. This work will provide training to students and re-introduce a class in fracture mechanics at Northern Arizona University. Outreach efforts will help recruit females and underrepresented minorities into engineering. Because this work focuses on women’s health, it will hopefully attract female students and demonstrate that engineering is an inclusive field. The researched work will advance our understanding of the mechanics of pelvic floor muscles, fracture, and episiotomies. The tasks include material modeling, evaluating the crack tip stresses from an episiotomy in closed-form and with finite element simulation, measuring the fracture toughness, and evaluating the energy release rate (J-integral). To develop a material model for these anisotropic, hyperelastic pelvic floor tissues, the mechanical behavior of rat pelvic floor tissues will be experimentally characterized. Different orientations of the muscle will be characterized so that the continuum-scale constitutive model can accurately capture the contributions of the extracellular matrix and the fibers from the microstructure. These constitutive relations will then be used in closed-form and computational (finite element) models to predict crack-tip stresses after various types of episiotomies. The fracture toughness will be experimentally determined using rat pelvic floor tissue with an induced notch at various angles relative to the muscle fibers. Ultimately the fracture toughness will be compared to the energy release rate from the finite element simulations to predict tearing after an episiotomy. This work will test the robustness of fracture theories by applying them to a whole new system to better understand the uses and limits of fracture mechanics. Moreover, this work will determine under what conditions (fetal head size, episiotomy geometry, and material properties) an episiotomy is likely to lead to severe tears. This important, practical information can be transferred to the clinical setting to improve the quality of care provided during childbirth. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.