478: Does LEEP specimen size influence the risk of preterm birth?

the risk of preterm birth? George A. Macones, Alison Cahill, David Stamilio, Kimberly Roehl, Anthony Odibo Washington University in St. Louis, Department of Obstetrics and Gynecology, St. Louis, MO, Washington University in St Louis, Department of Obstetrics and Gynecology, St Louis, MO OBJECTIVE: To assess whether increasing size of LEEP specimen is associated with an increasing risk of preterm birth. STUDY DESIGN: Reproductive-aged women who underwent LEEP between 2000-2006 were identified by a review of pathology records at 9 hospitals (both community and tertiary). Subjects were contacted via phone by trained research nurses, enrolled into the study, and underwent a detailed, closed-ended interview. Pathology records for all procedures, as well as all medical records preand post-LEEP, were obtained and reviewed by research staff. We assessed whether the size of LEEP as assessed by depth or volume (specimen volume depth x width x height) influenced the rate of preterm birth, by developing a multivariable model. The area under the ROC curve was used to evaluate the discriminatory efficiency of the models. RESULTS: We enrolled 625 women with a prior LEEP, of which 119 had a preterm birth in the first post-LEEP pregnancy (19%). There was no difference in the mean LEEP volume between women with a subsequent preterm birth and those with a subsequent term birth (2.4 cm3 vs 2.3 cm3, p 0.7). Likewise, there was no difference in mean LEEP depth between those who delivered preterm and thse who did not (1.88 cms vs 1.83 cms, p 0.53). Multivariable analysis also supported no association between LEEP volume and preterm birth (aOR 1.01, 95% CI 0.95-1.08) or depth and preterm birth (aOR 1.01, 95% CI 0.67-1.54). ROC curve of LEEP volume or depth and preterm birth was completely non-discriminating between those who delivered at term and those who delivered preterm, as evidenced by areas under the curve of 0.60 and 0.51 respectively. CONCLUSION: Increasing LEEP volume or depth is not associated with an increased rate of preterm birth 37 weeks. (Supported by RO1 CA109186) 479 Exploration of the human cervix using acoustic radiation force impulse (ARFI) measurements Helen Feltovich, Lisa Reusch, Mark Palmeri, Lindsey Carlsen, Timothy Hall Intermountain Healthcare, University of Wisconsin, University of Utah, Maternal-Fetal Medicine, Medical Physics, Provo, UT, University of Wisconsin, Medical Physics, Madison, WI, Duke University, Biomedical Engineering, Durham, NC OBJECTIVE: The cervix contains layers of collagen, which provide its strength. Remodeling must occur in pregnancy, but premature change may lead to premature birth. Recent animal studies suggest remodeling occurs differently in separate collagen layers, and that a dominant central layer undergoes the greatest change. Currently there is no objective, noninvasive method to assess cervical remodeling, particularly potential regional differences (eg due to differences in layers). Measurement of shear wave sound speeds (SWSS) in tissue can provide both objective measurement of softness (waves move slower in softer tissue) and suggest layers(wave behavior changes at boundaries). Acoustic radiation force impulse (ARFI) tools may allow these assessments. STUDY DESIGN: Hysterectomy specimens (n 6, 3 nulliand 3 multiparous) were scanned with a 3.3mm diameter transducer (Siemens) that fits into the cervical canal. Customized ARFI tools estimated peak displacement and SWSS at various depths in the tissue. Transmit and receive angles were electronically changed to assess wave propagation across the tissue (to assess for potential layers) at angles of 0 and / 20degrees. RESULTS: Peak displacements in all specimens were about 3um. Normalized displacements showed wave propagation across the cervix, indicating appropriate tracking of tissue response to acoustic force impulse. Shear wave dynamics suggested a layered structure. A consistent change in SWSS was seen at around 6mm in both nulliparous and multiparous tissue, suggesting a layer boundary that is preserved regardless of parity. Nulliparous cervices (no history of pregnancyassociated remodeling) showed greater homogeneity. CONCLUSION: ARFI tools appear to be able to identify collagen layers in the cervix. A comprehensive understanding of remodeling, including regional changes (eg within a specific layer), is essential to developing new approaches to preterm birth.