On the Prediction of Pelvic Floor Muscle Injury during Vaginal Delivery in Nullipara: Anthropometric and Viscoelastic Biomechanical Analyses

The goal of this research was to provide clinicians with a new framework for preventing pelvic floor muscle tears during vaginal birth. Currently these tears occur in 15% of first time mothers. In Chapter 2 we developed a theoretical anthropometric model to determine whether a fetal head could pass through the lower birth canal. In Chapter 3 we used a five parameter constitutive model to provide the first quantification of the viscoelastic behavior of the term-pregnant lower birth canal. In Chapter 4, we quantified the 400-fold variation in the longer of the two time constants among a cohort of 25 laboring nullipara. This was incorporated into the theoretical model to predict the length of the second stage of labor and the risk for pelvic floor muscle tear in these nullipara. In Chapter 5, we used secondary data from a clinical trial of the Materna device to test how well the models in Chapter 4 predicted the actual duration of the second stage of labor, and we also quantified the sensitivity and specificity of the pubovisceral muscle (PVM) tear predictions. In Chapter 6, we employed birth simulations to consider the differential effect of forceps and vacuum instrumentation, as well as episiotomy depth, on predicted PVM tear rates and duration of the active second stage of labor. In Chapter 7, we used birth simulation models to consider the effect of pre-distension of the birth canal during the first stage of labor on the predicted duration of the active second stage and on PVM tears. This dissertation provides a foundation and tool for clinicians to better discuss delivery options antenatally with women in order to prevent pelvic muscle tears, a focus which is generally lacking at present. The next step would be a prospective clinical trial to validate the model predictions.PHDBiomedical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/138732/1/voigtpai_1.pd