24th World Congress on Ultrasound in Obstetrics and Gynecology Short oral presentation abstracts Results: Fifty-one cases of TRAP sequence were identified during this study period. The mean gestational age at first presentation was 17.8 ± 3.6 weeks. 48 cases of them were twin pregnancies and 3 were triplet. The types of TRAP pair were 36 monochorionic diamniotic (MCDA) cases, 11 monochorionic monoamniotic(MCMA) cases, and 4 unknown cases. Thirty-two women underwent RFA. The mean gestational age at RFA was 21.1 ± 2.0 weeks. We confirmed the cessation of blood flow in all cases. In 29 cases of 32 in which prognosis were known, there were 27 live births and the mean gestational age at delivery was 37.5 ± 3.6 weeks. Two postoperative pump twin demise occurred because of umbilical cord entanglement of MCMA twin. In 19 cases without RFA, 15 cases were managed expectantly, 3 cases opted termination of pregnancies and 1 case was performed high-intensity focused ultrasound in another hospital. In 15 expectant managed pregnancies except 1 case lost follow-up, 7 cases of spontaneous death of the pump twin, 3 cases of spontaneous cessation of reversed flow toward acardiac twin occurred; whereas, 4 cases continued the reversed flow. The mean gestational age at birth of expectant managed cases was 31.5 ± 3.4 weeks. Conclusions: RFA for TRAP sequence was effective and showed good pregnancy outcomes. Half of expectant management cases resulted in pregnancy losses. Applications of RFA and treatment options for TRAP sequence before 16 weeks of gestation should be reconsidered. OP34.06 Development of survival rates after intrauterine laser therapy for severe twin–twin transfusion syndrome in a series of 851 consecutive cases W. Diehl, A.M. Diemert, P. Glosemeyer, M. Tavares de Sousa, K. Wegscheider, K. Hecher Universit ¨ atsklinikum Hamburg-Eppendorf, Hamburg, Germany Objectives: To analyse the development of survival rates with increasing surgical experience in 851 cases of severe mid-trimester twintwin transfusion syndrome (TTTS) treated with fetoscopic laser coagulation (FLC) of placental anastomoses. Methods: A series of consecutive cases of severe TTTS between 17 to 27 weeks of gestation treated from 1995 to 2011 was divided into four groups. The first three groups consisted of 200 consecutive cases each and were reported formerly. To complete the analysis of the development of survival rates for a second surgeon, trained in the same center by an experienced surgeon, a fourth group of further 251 consecutive cases was added to complete 100 procedures done by the second surgeon. The analysis of the trainee learning curve in terms of survival rates compares to the rates of the experienced surgeon in the respective time period. Results: For double neonatal survival the rates increased from 50.0% and 59.5% up to 69.0% in groups 1, 2 and 3, respectively. Thereafter in group 4 the rates showed no further increase. Accordingly, the percentage of pregnancies with no or only one survivor, that decreased from 19.5% to 16.5% and to 10.5%, and from 30.5% to 24.0% and to 20.5%, in groups 1, 2 and 3 respectively, did not decrease further. For overall survival and cases with survival of at least one twin, rates increased from 65.3% to 71.5% and to 79.3% and from 80.5% to 83.5% and to 89.5% in groups 1, 2 and 3, respectively, but showed no further increase in group 4. Survival rates of the procedures performed by the trainee surgeon were 71.0%, 89.0% and 80.0% for 2 survivors, at least 1 survivor and overall survival, respectively. Conclusions: Although growing experience in FLC for severe TTTS contributes to increasing survival rates these seem to remain stable when reaching 62.5% for 2 survivors, 85.8% for at least 1 survivor and 74.1% for overall survival. After 100 procedures the trainee surgeon achieved similar survival rates as compared to the stable rates of the experienced surgeon. OP34.07 The role of echocardiography in the intraoperative management of the fetus undergoing myelomeningocele repair J. Rychik 1 , Z. Tian 1 , A. Szwast 1 , S. Natarajan 1 , J. Moldenhauer 2 , M.P. Johnson 2 , N. Adzick 2 1 Fetal Heart Program, The Children’s Hospital of Philadelphia, Philadelphia, PA, USA; 2 Center for Fetal Diagnosis and Treatment, The Children’s Hospital of Philadelphia, Philadelphia, PA, USA Objectives: Fetal surgery for myelomeningocele (MMC) results in better outcomes compared to postnatal treatment, however maternal and fetal risks are present. We describe our experience with intraoperative fetal echocardiography (FE) during repair of MMC, and report management of serious intraoperative cardiovascular events (CVE). Methods: Subjects include fetuses with intent to repair MMC from Jan 2011-Feb 2014. FE protocol involves continuous assessment in a looping, sequential manner from uterine incision until closure of 1) 2D qualitative ventricular systolic function, 2) heart rate (HR) via pulse-wave Doppler sampling above the aortic valve, and 3) color Doppler of tricuspid (TR) and mitral valve regurgitation (MR). Results: 101 cases intended fetal MMC repair; 100 completed surgery. At preoperative screening, no cardiovascular abnormalities were noted. Intraoperative ventricular dysfunction was present in 60% (20 mild, 25 moderate, 15 severe). HR < 100 was noted in 11 cases. TR was present in 35% (26 mild, 7 moderate, 2 severe); MR was present in 19% (15 mild, 4 moderate). 7 cases experienced serious CVE, which affected conduct of surgery and/or outcome. 4 had bradycardia and severe dysfunction. Medications were given via umbilical vein and external cardiac compressions performed. FE was used to gauge efficacy of compressions and guide resuscitation. HR and cardiac function improved after 7-10 minutes of compressions and MMC repair was completed. 1 had bradycardia and dysfunction, improvement without medications, but asystole was noted following uterine closure. 1 had bradycardia prior to uterine incision and surgery was aborted. 1 had bradycardia, dysfunction and a large left atrial thrombus and responded to medications without compressions. Conclusions: Cardiovascular compromise is common during fetal surgery for MMC. Intraoperative FE is recommended as a growing number of centers contemplate offering this form of novel, but potentially risky therapy for their patients. OP34.08 Early results of a new fetoscopic technique for the correction of spina bifida beyond 26 weeks of gestation: can we move the upper limit for the surgery? D.A. Pedreira 1,2 , N.C. Zanon 3,2 , R.A. Sa 2 , G.L. Acacio 2 , V. Zito 2 , E. Ogeda 2 , L. Collange 2 , R. Pincerato 2 , P.S. Oliveira 3 , T. Uras 2 1 Pathology, University of Sao Paulo, Sao Paulo, Brazil; 2 Centro de Medicina Fetal e Perinatal, Hospital Samaritano de S ˜ ao Paulo, SAO PAULO, Brazil; 3 Neurosurgery, UNIFESP, Sao Paulo, Brazil Objectives: Open fetal surgery for correction of spina bifida is currently been offered before 26w, due to the lower reduction of the need to place a VP-shunt, when surgery is performed after this point. We will report on the impact of operating SB beyond 26 weeks, using a new surgical technique. Methods: We report on 5 fetus with lumbo-sacral spina bifida, operated before 28 weeks. Under general anesthesia, we used a fetoscopic approach with 3 trocars and partial CO2 insuflation of the uterine cavity. Defect correction was accomplished by the 174 Ultrasound in Obstetrics & Gynecology 2014; 44 (Suppl. 1): 62–180.