Ingenium 2020
Changes to the maternal sacrum and coccyx during and after pregnancy and delivery Liam Martina, Megan R. Routzong, BSa, Ghazaleh Rostaminia, MD, MScb, Pamela A. Moalli, MD, PhDc, Steven D. Abramowitch, PhDa Translational Biomechanics Laboratory, Department of Bioengineering, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA, USA b Female Pelvic Medicine and Reconstructive Surgery (PFMRS), Division of Urogynecology, University of Chicago Pritzker School of Medicine, Northshore University HealthSystem, Skokie, IL, USA c Department of Obstetrics, Gynecology & Reproductive Surgery, University of Pittsburgh, Pittsburgh, PA, USA; Magee-Womens Research Institute, Pittsburgh, PA, USA a
Liam Martin
Liam Martin is a senior bioengineering student on the biomechanics track with a minor in mechanical engineering. He has worked for ten months in the Translational Biomechanics Laboratory where he has worked to help describe the effects of pregnancy and delivery on the maternal bony pelvis.
Dr. Abramowitch received his B.S. (1998) in Applied Mathematics and Ph.D. (2004) in Bioengineering from the University of Pittsburgh. Currently, he is an Associate Professor in the Department of Bioengineering and serves as the Director of the Translational Biomechanics Dr. Steven D. Laboratory. This past October he was the Abramowitch recipient of the Biomedical Engineering Society (BMES)diversity lecture award at the national conference in Philadelphia. Dr. Abramowitch’s research focuses on understanding the impact of pregnancy, delivery, and other life events (aging, menopause, etc.) on the structural integrity of the pelvic floor in women.
Significance Statement
Changes to the maternal pelvis during pregnancy and after delivery have yet to be robustly quantified, but could eventually allow for identification of women at risk of sustaining injury during vaginal delivery. By looking at the combined maternal sacrum-coccyx shape, we found significant posterior movement of the coccyx with respect to the sacrum during pregnancy and, in some women, after delivery.
Category: Computational research
Keywords: Delivery, Pregnancy, Maternal bony pelvis
Abstract
Hormonal changes during pregnancy cause tissue remodeling, presumably to facilitate vaginal delivery. This study aimed to determine whether softening of maternal tissues results in sacrumcoccyx shape changes by comparing measurements between nulliparous (have never given birth), gravid (pregnant), and parous (have given birth) women. We hypothesized that these measures would differ significantly between groups and be consistent with remodeling that would facilitate vaginal delivery (i.e. posterior movement of the coccyx to accommodate the fetus). Assuming that some women do not fully recover from delivery, we expect to see differences between all three groups. Sacrum and coccyx features were measured by analyzing pelvic MRI scans. Of the 12 measures performed, 3 had significant univariate results: coccygeal curvature index (p<0.001), sacrococcygeal curvature index (p<0.001), and sacrococcygeal angle (p=0.010). Only the nulliparous and gravid groups differed significantly, while the parous values straddled both groups. The results of this study support the hypothesis that pregnancy results in significant changes to the combined maternal sacrum/coccyx shape that are consistent with those more favorable for vaginal delivery and implies that lasting changes occur during pregnancy and/or delivery. Additionally, when dividing these groups into subgroups defined by parity (number of deliveries), larger shape changes were quantified with increasing parity in the gravid group. Because our gravid patients had yet to give birth vaginally (vaginally nulliparous), these changes are likely due to pregnancy alone as a C-section is not expected to affect pelvic shape. This suggests that pregnancy, despite mode of delivery, can result in unrecoverable pelvic shape changes.
1. Introduction
Hormonal changes during pregnancy are known to cause tissue remodeling, resulting in connective tissue laxity at the pubic symphysis and sacroiliac joints presumably to facilitate vaginal delivery [1]. The tissue laxity and remodeling allow for the maternal pelvis to accommodate the growing fetus. Previous work by our lab demonstrates the need for this tissue laxity as the sacrum and coccyx significantly engaged with the fetal head during simulations of vaginal delivery: the mechanical load introduced by the fetal head pushed the coccyx posteriorly, forcing the muscles and connective tissues anchored and engaged with these bones to stretch [2]. This suggests three potential sources for persistent pelvic shape changesâ&#x20AC;&#x201D;increases in intraabdominal pressure due to the growing fetus, tissue remodeling during pregnancy, and/or injury during vaginal delivery. If the coccyx is moved during delivery, it is reasonable to assume that tissue remodeling during pregnancy may make this motion easier. Other studies have shown significant movement of maternal bony structures during pregnancy, though sacrum and coccyx shape specifically have yet to be investigated [3,4]. Tissue remodeling along with mechanical strain from the fetus have been found to cause lower spine and pubic symphysis pain that can persist after pregnancy and delivery [5]. Also, there are other studies that show that there are many changes that occur on the pelvic floor muscles [6]. It is 63
