Z48 - Uterine Tissue Remodeling following Hysterotomy and Postpartum Involution

Friday, October 10, 2025

10:00 AM - 11:00 AM PDT

Location: Exhibit Hall F, G & H

Presenting Author(s)

Matthew R. Bersi, PhD

Assistant Professor, Mechanical Engineering & Materials Science
Washington University in St. Louis
St. Louis, Missouri, United States

Last Author(s)

Matthew R. Bersi, PhD

Assistant Professor, Mechanical Engineering & Materials Science
Washington University in St. Louis
St. Louis, Missouri, United States

Primary Investigator(s)

Matthew R. Bersi, PhD

Assistant Professor, Mechanical Engineering & Materials Science
Washington University in St. Louis
St. Louis, Missouri, United States

Introduction: : During pregnancy, the uterus must stretch significantly to accommodate the growing fetus and the myometrium strongly contracts during labor to promote a successful vaginal delivery. However, in circumstances where labor and vaginal delivery is not possible due to anatomical, medical, or fetal positioning challenges, the patient must undergo delivery via Cesarean section. After surgery and closure, any improper healing of the Cesarean scar placed through the uterus can lead to weakening of the tissue which may result in uterine rupture in subsequent pregnancies. Uterine rupture is defined as a serious complication where the uterine wall tears open leading to life-threatening complications. The ruptures are thought to transpire due to the force of contractions impacting areas of tissue weakening in the uterus, causing it to fail prematurely. This can occur around existing uterine scar sites in women who attempt a vaginal birth after a previous Cesarean delivery. The majority of uterine ruptures occur during labor, but it can also take place during pregnancy. Understanding the mechanisms of uterine healing is critical to uncovering the causes of uterine rupture and improving outcomes in reproductive health. This study investigates the expression of elastin and other extracellular matrix components throughout the process of post-surgical and postpartum healing to better understand how the uterus heals over time and why uterine ruptures occur.

Materials and

Methods: : Wildtype female mice were anesthetized and a hysterotomy procedure to induce uterine scar formation was performed by creating two 3 mm incisions on each uterine horn. Following incision closure, uterine horns were collected at 9 or 12 weeks post-hysterotomy to complement prior data at earlier post-surgery times (e.g., 1, 3, and 6 weeks). Additional mice were mated at 6 weeks post-hysterotomy and uterine horns were excised a different postpartum timepoints (e.g., 1, 7, and 21 days) after labor and delivery.

Using optical coherence tomography (OCT) imaging, uterine samples were scanned to non-invasively visualize the internal wall structure. This approach allowed the uterine scar area to be identified throughout several layers of the wall and aided in preparing samples for histological staining and analysis.

Following examination by OCT, a cryotome was utilized to create 8 um sections of frozen embedded tissues for histological and immunofluorescent staining and analysis. Slides were prepared for picrosirius red (PSR) staining by performing a series of reagent washes prior to placing in picrosirius red solution for 1 hour according to manufacturer protocols. Additionally, immunofluorescent staining for expression of α-smooth muscle actin (α-SMA) and elastin was performed. Together, these stains allowed us to visualize and compare uterine wall microstructure in scarred, postpartum, and healthy tissues. Microscopic imaging was conducted on an Olympus BX53 microscope at 20x magnification. Data analysis was performed for each staining method to identify the percentages of each factor in the tissue samples.

Results, Conclusions, and Discussions:: Regions of discontinuous uterine tissue and acellularity visible in the OCT images revealed where the scar area was present after hysterotomy. PSR staining of post-hysterotomy tissues revealed a predominance of densely packed red-orange collagen whereas yellow-green signifies loosely packed collagen. Over time, we observed reduced red-orange collagen and increased yellow-green collagen at 1 week (p < 0.05) that resolved by 12 weeks post-surgery (Fig.1). Interestingly, postpartum time points tended to have more red-orange collagen and less yellow-green collagen than 6 week post-surgery non-pregnant tissues. This suggests there is collagen matrix remodeling during gestation that normalizes by 21 days postpartum (Fig.2) Elastin was elevated in scarred tissue at 9 weeks post-surgery relative to control and α-SMA expression was notably higher in the myometrium during postpartum healing and at 9 weeks post-surgery. Together, this may suggest either increased smooth muscle contractility or myofibroblast activity during uterine healing (Fig.3).

This study is not without limitations. OCT can only image a few millimeters into soft tissue and this limited depth penetration makes it difficult to identify scar areas in the uterus. Additionally, dense fibrotic tissue areas limit the OCT imaging capabilities. PSR staining reveals collagen fiber organization in scars or areas of structural remodeling but cannot determine which collagen types are upregulated. Elastin provides elasticity and support to soft tissues while α-SMA indicates the presence of contractile cells. Interestingly, both elastin and α-SMA expression were elevated after uterine scarring and postpartum healing. Together, this indicates significant uterine remodeling is required for wound healing.

Our findings in this study highlight the complex and active process of uterine wound healing, marked by microstructural changes in collagen, elastin, and smooth muscle cells in the uterine wall. These biological insights bring us closer to understanding uterine wound healing which may eventually provide mechanistic insight into why uterine rupture occurs. Combining these microstructural observations with direct mechanical measurements of uterine tissue integrity will be important moving forward. By uncovering the tissue-level mechanisms behind uterine repair, this research aims not only to advance medical knowledge but also to support safer childbirth experiences and offer hope for improved outcomes in reproductive health.

Acknowledgements and/or References (Optional): :