LAUSR

1051 Likelihood of vasa previa resolution across gestation Nathan S. Fox, Rebecca A. Klahr, Kelly B. Zafman, Melissa B. Hill, Courtney T. Connolly, Andrei Rebarber Icahn School of Medicine at Mount Sinai, New York, NY, Maternal Fetal Medicine Associates, PLLC, New York, NY OBJECTIVE: Vasa previa (VP) is a rare obstetric condition defined by the presence of fetal blood vessels overlying or close to the internal cervical os. The purpose of this study was to identify the resolution rate of vasa previa across gestation and to determine clinical and sonographic factors that are predictive of VP resolution. STUDY DESIGN: Retrospective cohort study of women diagnosed with VP in a single ultrasound unit between 2005 and 2018. VP was defined as a fetal vessel within 2 cm of the internal cervical os on transvaginal ultrasound. The primary outcome was VP resolution, defined as migration of the VP to >2cm away from the internal os. All images were re-reviewed. Chisquare, student t-test and logistic regression analysis was performed to determine variables significantly associated with VP resolution. RESULTS: 100 women with VP were included, diagnosed at a mean GA of 22.8 +/4.9 weeks. 39 women (39.0%) had resolution of VP at a mean gestational age of 28.6 +/4.7 weeks. Factors associated with VP resolution on univariate and regression analysis were earlier GA at diagnosis (aOR 6.10), VP not covering the internal os at diagnosis (aOR 8.29) and VP not being the result of a resolved placenta previa (aOR 2.85). The Table shows the likelihood of VP resolution in all women as well as based on the initial location of the VP. Factors not associated with VP resolution were maternal age, parity, IVF, number of fetuses, vessel type (artery, vein, or both), CL at diagnosis, velamentous cord insertion, 2-vessel umbilical cord, succenturiate lobe, uterine anomalies, and fibroids. One woman with twin pregnancy and VP resolution (at 31 weeks, 2.8cm from the internal os) presented at 33 weeks with massive bleeding and fetal demise of twin A. It was unclear if the demise was related to VP or placental abruption. CONCLUSION: 39% of vasa previas will resolve over the course of pregnancy. Earlier GA at diagnosis, VP not covering the internal os, and not having a resolved placenta previa are all independently