Medical Student Pacific Northwest University of Health Science Yakima, Washington, United States
Abstract Body : Clinical pelvimetry and Caldwell-Moloy classification of pelvic types are presented as reliable techniques to assess fetopelvic disproportion and risk of complicated birth. However, recent work highlights the lack of data correlating pelvic inlet shape to birth outcome and the clinical application of these predictive metrics. Our aim is to examine the biomechanical effects of maternal pelvic shape on the neonatal cranium using finite element analysis. If maternal pelvic shape influences birth outcome, we expect to find a correlation of the biomechanical forces exerted on the neonatal cranium and observed deformation and strain.
Neonatal CT-scans were acquired from the New Mexico Decedent Image Database. A female noted as near the ideal weight of a newborn by Caldwell- Moloy was selected based on cranial condition, term birth history, and age less than 1 month. Cranial imaging data was reconstructed as a surface mesh using the Biomesh FE modeling protocol. Cortical bone, sutures and fontanelles were modeled as manifolds, the cranium was meshed as a volumetric model and imported to Strand7 (Strand7 Pty Ltd, Sydney), where experimentally derived material properties of bone and sutures from the literature were assigned. To estimate boundary conditions, a surface model was constructed of an adult female bony pelvis using CT data from the Visible Human Project. The surface mesh was adjusted to result in four distinct pelvic models matching the morphotypes described by Caldwell-Moloy. Each pelvis was aligned with the neonatal cranium and linear static analysis was used to model the neonatal cranial bones and sutures as they passed through the four assigned maternal pelvis shapes during a volitional push.
Resulting deformation and strain patterns in the neonatal cranium were similar across all four maternal pelvis categories. Although some minor variation in strain magnitude was observed across the models, differences in pelvic shape failed to produce meaningful differences in the biomechanics of the neonatal head. This supports the hypothesis that the Caldwell Moloy pelvic classifications have no effect on strain patterns of the neonatal cranium during birth, and by extension likely has no effect on the difficulty of vaginal birth. These findings add to other research to further disprove the outdated Caldwell Moloy classification system.
In future work, our neonatal model could be used to examine the differences in force and strain patterns for operative vaginal deliveries and varied birth presentations. This work could be combined with geometric morphometric analysis to understand how the range of pelvic variation across global populations may affect the mechanical impact of these interventions on the fetal head and on maternal and fetal mortality.
