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The mechanical function of the uterus is critical for a successful pregnancy. During gestation, uterine tissue grows and stretches to many times its size to accommodate the growing fetus, and it is hypothesized the magnitude of uterine tissue stretch triggers the onset of contractions. To establish rigorous mechanical testing protocols for the human uterus in hopes of predicting tissue stretch during pregnancy, this study measures the anisotropic mechanical properties of the human uterus using optical coherence tomography (OCT), instrumented spherical indentation, and video extensometry. In this work, we perform spherical indentation and digital image correlation to obtain the tissue’s force and deformation response to a ramp-hold loading regimen. We translate previously reported fiber architecture, measured via optical coherence tomography, into a constitutive fiber composite material model to describe the equilibrium material behavior during indentation. We use an inverse finite element method integrated with a genetic algorithm (GA) to fit the material model to our experimental data. We report the mechanical properties of human uterine specimens taken across different anatomical locations and layers from one non-pregnant (NP) and one pregnant (PG) patient; both patients had pathological uterine tissue. Compared to NP uterine tissue, PG tissue has a more dispersed fiber distribution and equivalent stiffness material parameters. In both PG and NP uterine tissue, the mechanical properties differ significantly between anatomical locations.

Uterine cervical collagen fiber network is vital to the normal cervical function in pregnancy. Previously, we presented an orientation estimation method to enable dispersion analysis on a single axial slice of human cervical tissue obtained from the upper half of cervix using optical coherence tomography (OCT). How the collagen fiber network structure changes from the internal os (top of the cervix which meets the uterus) to external os (bottom of cervix which extends into the vagina), remains unknown due to depth penetration limitations of OCT. To establish a collagen fiber directionality “map” of the entire cervix, we imaged serial axial slices of human NP (n=11) and PG (n=2) cervical tissue obtained from the internal to external os using Institutional Review Board approved protocols at Columbia University Medical Center. Each slice was divided into four quadrants. In each quadrant, we stitched multiple overlapped OCT volumes and analyzed the en face images that were parallel to the surface. A pixel-wise directionality map was generated. We analyzed fiber trend by measuring the mean angles and quantified dispersion by calculating the standard deviation of the fiber direction over a region of 400 μm × 400 μm. For the initial four samples, our analysis confirms a circumferential fiber pattern in the outer region of slices at all depths. We found that the standard deviation close to internal os showed no significance to the standard deviation close to external os (p>0.05), indicating comparable dispersion.

The changes in the mechanical integrity of the cervix during pregnancy have implications for a successful delivery. Cervical collagens are known to remodel extensively in mice with progressing gestation leading to a soft cervix at term. During this process, mature crosslinked collagens are hypothesized to be replaced with immature less crosslinked collagens to facilitate cervical softening and ripening. To determine the mechanical role of collagen crosslinks during normal mouse cervical remodeling, tensile load-to-break tests were conducted for the following time points: nonpregnant (NP), gestation day (d) 6, 12, 15, 18 and 24 hr postpartum (PP) of the 19-day gestation period. Immature crosslinks (HLNL and DHLNL) and mature crosslinks (DPD and PYD) were measured using ultra performance liquid chromatography-electrospray ionization tandem mass spectrometry (UPLC-ESI-MS/MS). There were no significant changes in the total immature crosslink density (HLNL+DHLNL mol per collagen mol) throughout normal mouse gestation (range: 0.31-0.49). Total mature crosslink density (PYD+DPD mol per collagen mol) decreased significantly in early softening from d6 to d15 (d6: 0.17, d12: 0.097, d15: 0.026) and did not decrease with further gestation. The maturity ratio (total mature to total immature crosslinks) significantly decreased in early softening from d6 to d15 (d6: 0.2, d15: 0.074). All of the measured crosslinks correlated significantly with a measure of tissue stiffness and strength, with the exception of the immature crosslink HLNL. This data provides quantitative evidence to support the hypothesis that as mature crosslinked collagens decline, they are replaced by immature collagens to facilitate increased tissue compliance in the early softening period from d6 to d15.

diamniotic twin pregnancies: comparison of neonatal outcomes at late preterm gestational ages Hen Sela, Alexandra Kass, Ananth Cande, David Bateman, Joy-Sarah Vink, Karin Fuchs, Russell Miller, Lynn Simpson, Mary E. D’Alton Columbia University Medical Center, Obstetrics and Gynecology, Division of Maternal Fetal Medicine, New York, NY, Columbia University Medical Center, Department of Obstetrics and Gynecology Division of Maternal Fetal Medicine, New York, NY, Columbia University Medical Center, Obstetrics & Gynecology, New York, NY, Columbia University Medical Center, Pediatrics-Neonatology, New York, NY, Columbia University Medical Center, Obstetrics and Gynecology, Division of Maternal Fetal Medicine, New York, NY, Columbia University Medical Center, Obstetrics and Gynecology, New York, NY OBJECTIVE: The optimal time to deliver uncomplicated monochorionic-diamniotic (MCDA) twins remains uncertain. We compared neonatal outcomes of uncomplicated MCDA twins electively delivered at different late preterm gestational ages. STUDY DESIGN: A retrospective cohort study of all MCDA twins delivered at a single tertiary care center between 2003-10 was performed. Late preterm were defined as gestational ages of 340/7-356/7 weeks and uncomplicated MCDA twins were defined as concordantly grown twins without evidence of fetal growth restriction or growth discordance 20%, normal anatomical surveys, no chromosomal abnormalities, normal amniotic fluid volumes and normal Dopplers of selected fetal vessels. Higher-order multiples, MCDA resulting from fetal reduction, cases of twin-twin transfusion syndrome, placental abruption, PPROM, and preeclampsia at 32 weeks gestation were excluded. Planned delivery was defined as either elective induction or cesarean. Deliveries that were either spontaneous or indicated were considered non-planned (NP). Neonatal outcomes were compared between 34-35 weeks, 34-36 weeks and 35-36 weeks. All analyses were adjusted for the intracluster correlation due to twinning. RESULTS: During the study period, 134 of 482 MCDA twins (27.8%) meet inclusion/exclusion criteria. Forty-three (30%) pregnancies were delivered at 34 weeks, 33 (23%) delivered at 35 weeks and 58 (40%) delivered at 36 weeks. Results of performed comparisons are detailed in the table. CONCLUSION: During the study period, 134 of 482 MCDA twins (27.8%) were uncomplicated and delivered 34 weeks. Forty-three (30%) pregnancies were delivered at 34 weeks, 33 (23%) delivered at 35 weeks and 58 (40%) were delivered at 36 weeks. Results of performed comparisons are detailed in the table. There were very few difference in neonatal outcome between planned versus non-planned delivery at 34 weeks, 35 weeks, or 36 weeks. Compared to planned deliveries at 34 and 35 weeks, planned deliveries at 36 weeks were associated with better neonatal outcomes. 171 Iatrogenic early term delivery and risk of adverse neonatal outcomes Jaclyn Coletta, Kobina Ghartey, Liza Lizarraga, Elizabeth Murphy, Cande Ananth, Cynthia Gyamfi Columbia University Medical Center, Obstetrics and Gynecology, Division of Maternal Fetal Medicine, New York, NY, Columbia University Medical Center, Obstetrics and Gynecology, New York, NY OBJECTIVE: Although considered full term, infants born between 37-38 weeks gestation are at increased risk for adverse outcomes compared to those delivered at 39 wks. Since delivery occurs at 37 weeks for a variety of indications, we sought to determine whether adverse neonatal outcomes after a spontaneous onset of labor at 37-38 weeks gestation were similar to adverse outcomes resulting from nonspontaneous labor. STUDY DESIGN: This is a retrospective cohort of singleton, non-anomalous early term (ET) deliveries (37 0/7 to 38 6/7 weeks gestation) from January to December 2010 at a single institution. Baseline maternal characteristics and neonatal outcomes were abstracted from medical records. Women presenting in spontaneous labor (via intact or ruptured membranes) and who went on to deliver vaginally or by cesarean were compared to those delivered for a non-spontaneous indication (via labor induction or scheduled cesarean). Our primary outcome was a composite neonatal morbidity adapted from a prior ET study –NICU admission, oxygen use, CPAP, ventilator support, respiratory distress syndrome, transient tachypnea of the newborn, hypoglycemia, sepsis, seizures, necrotizing enterocolitis, or hypoxic ischemic encephalopathy. RESULTS: 1,169 women delivered in the ET period; 712 (61%) presented in spontaneous labor and 457 (39%) were non-spontaneous. The groups were similar in maternal demographics, however the spontaneous group was older (38.0 wks versus 37.9 wks, p 0.001), and less likely to be exposed to steroids (2.1% versus 6.6%, p 0.001). In the univariate model, there was a significant decrease in the composite adverse outcome in neonates that were delivered spontaneously (Table). After adjusting for confounders, this finding held true (p 0.003). CONCLUSION: Neonates of women who labor spontaneously in the ET period are less likely to experience morbidity when compared with neonates from women from all non-spontaneous indications. The increased morbidity in the non-spontaneous group suggests careful consideration to the indication when electing to deliver a patient prior to 39 weeks. www.AJOG.org Clinical Obstetrics, Medical-Surgical-Disease, Neonatology, Physiology-Endocrinology Poster Session I