643: First stage of labor in women undergoing trial of labor after cesarean: what should the expectations be?

643 First stage of labor in women undergoing trial of labor after cesarean: what should the expectations be? Anna Graseck, Anthony Odibo, Methodius Tuuli, Kimberly Roehl, George Macones, Alison Cahill Washington University in St. Louis, Department of Obstetrics and Gynecology, St. Louis, MO OBJECTIVE: The natural history of the first stage of labor is virtually unknown in women attempting trial of labor after cesarean (TOLAC), but vitally important to the clinician. Many have hypothesized that a different standard should be used to diagnose protraction and arrest in TOLAC. We aimed to compare first stage labor patterns in women undergoing TOLAC and those without a prior cesarean section to explore whether a uterine scar alters this stage of labor. STUDY DESIGN: A retrospective cohort study was conducted of all consecutive term, vertex singletons from 2004-2008 who reached the second stage of labor. Extensive data were collected from medical records, including cervical exams (allowing complete reconstruction of labor curves) and obstetric and neonatal outcomes. Women undergoing TOLAC were compared to those without a history of cesarean section. A repeated-measures analysis was used to construct average labor curves, stratified by TOLAC status. Interval-censored regression was used to estimate duration of labor, centimeter by centimeter, stratified by TOLAC status and adjusted for race, maternal obesity, fetal macrosomia, and prior vaginal delivery. RESULTS: Of 5,388 consecutive term births, 2,021 labored spontaneously, 1,720 were augmented, and 1,647 induced. Of the women laboring spontaneously, 1,881 (93%) women with no prior cesarean delivery were compared to 140 (7%) women undergoing TOLAC. There was no significant difference in rates of cervical dilation between the groups in unadjusted and adjusted analyses. The median time for dilation from 4 to 10 cm was 3.0 hours for TOLAC and 2.8 hours for non-TOLAC (p 0.52). In subgroup analyses of those without a prior vaginal delivery, median time of active phase of labor did not differ by presence of a uterine scar (3.7 hours in both groups, p 0.95). CONCLUSION: There is no significant difference in first stage labor curves or cervical dilation rate between women undergoing TOLAC and those without a prior cesarean section. Thus, diagnoses of protraction and arrest should be made with similar standards between those with and without a uterine scar. 644 A silk-based injectable biomaterial as an alternative to cervical cerclage: an in-vitro study Asha Heard, Simona Socrate, Kelly Burke, Errol Norwitz, David Kaplan, Michael House Tufts Medical Center, Obstetrics & Gynecology, Division of Maternal-Fetal Medicine, Boston, MA, Massachusetts Institute of Technology, HarvardMIT Division of Health Sciences & Technology, Cambridge, MA, Tufts University, Department of Biomedical Engineering, Medford, MA, Tufts University School of Medicine, Obstetrics & Gynecology, Boston, MA OBJECTIVE: To develop an injectable biomaterial as an alternative to cervical cerclage. STUDY DESIGN: Human cervical tissue specimens were obtained from premenopausal gynecological hysterectomies for benign indications. A three part biomaterial was formulated, which consisted of purified silk protein solution (10% w/v) blended with a two part polyethylene glycol (PEG) gelation system. The chemically active PEG gelation system consisted of 4-arm PEG maleimide (10 kDa) and 4-arm PEG thiol (10 kDa). Solution A was PEG maleimide (10% w/v) in silk solution. Solution B was PEG thiol (10% w/v) in silk solution. The two solutions were injected into cervical tissue using a double barrel syringe with a mixing tip and a 20 gauge needle. After injection, the tissue was placed in absolute alcohol for 10 minutes to accelerate beta sheet formation in the silk. The injected tissue was evaluated for mechanical properties and swelling using standardized and validated test protocols performed in triplicate. Controls included uninjected tissues and tissues injected with PEG only. Cytocompatibility was tested with primary human cervical fibroblasts. RESULTS: Initial gelation of the silk/PEG biomaterial occurred 5 seconds after injection due to cross-link formations between thiol and maleimide functional groups. Further stiffening occurred with silk beta sheet formation. The mean SD increase in tissue wet weight after injection was 17.0 6.7%. The peak stress at 25% compressive strain was doubled in the injected tissue compared to uninjected controls (p 0.001). Swelling properties of injected tissue were no different than native tissue controls. However, swelling was significantly increased (p 0.001) if silk was not used (PEG only). Cervical cells remained viable for 48 hours when cultured on the biomaterial. CONCLUSION: We report a silk-based, biocompatible, injectable biomaterial for potential treatment of cervical insufficiency. Injected cervical tissue was twice as stiff as uninjected controls. Animal studies are needed to assess this biomaterial in-vivo. PosterSessionIV Epidemiology, Infectious Disease, Intrapartum Fetal Assessment, Operative Obstetrics, Obstetric Quality & Safety, Public Health-Global Health www.AJOG.org