OBSTETRICS Residual anastomoses in twin-to-twin transfusion syndrome treated with selective fetoscopic laser surgery: localization, size, and consequences Enrico Lopriore, MD, PhD; Femke Slaghekke, MD; Johanna M. Middeldorp, MD, PhD; Frans J. Klumper, MD; Dick Oepkes, MD, PhD; Frank P. Vandenbussche, MD, PhD OBJECTIVE: To study the localization and size of residual anastomo- ses in twin-to-twin transfusion syndrome treated with fetoscopic laser surgery and correlate the findings with outcome. STUDY DESIGN: Placental injection in twin-to-twin transfusion syn- drome placentas treated with laser was performed by using colored dye. RESULTS: A total of 77 twin-to-twin transfusion syndrome placentas were included in the study. Residual anastomoses (n = 48) were found in 32% (25/77) of lasered placentas. Most residual anastomoses were localized near the margin of the placenta. The majority of residual anastomoses (67%; 32/48) were very small (diameter,  1 mm). Eleven of the 25 cases (44%) in the residual anastomoses group de- veloped twin anemia-polycythemia sequence. CONCLUSION: Most residual anastomoses in twin-to-twin transfusion syndrome placentas treated with laser are very small and localized near the placental margin. Almost half of cases with residual anastomoses developed twin anemia-polycythemia sequence after laser surgery. Key words: fetoscopic laser coagulation of vascular anastomoses, residual anastomoses, twin anemia-polycythemia sequence, twin-to- twin transfusion syndrome Cite this article as: Lopriore E, Slaghekke F, Middeldorp J, et al. Residual anastomoses in twin-to-twin transfusion syndrome treated with selective fetoscopic laser surgery: localization, size, and consequences. Am J Obstet Gynecol 2009;201:x.ex-x. T win-to-twin transfusion syndrome (TTTS) affects approximately 15% of monochorionic twin pregnancies and results from unbalanced intertwin blood flow between the donor and the recipient twin through placental vascular anasto- moses. Untreated, TTTS is associated with high perinatal mortality and mor- bidity. 1 Fetoscopic laser occlusion of the vascular anastomoses is currently the best treatment option for TTTS. 2 The aim of laser surgery is to separate com- pletely both fetal circulations by occlud- ing all placental vascular anastomoses. However, several studies have shown that residual anastomoses (RA) may still be present after laser surgery and can be detected in up to 33% of lasered placen- tas. 3,4 RA may lead to recurrence of TTTS in 14% of cases and twin anemia- polycythemia sequence (TAPS) in 13% of cases. 5 The aim of this study was to measure the size of the RA and determine the lo- calization of the RA in relation to the margin of the placenta. A secondary aim of this study was to determine the asso- ciation between RA and hematologic complications at birth. MATERIALS AND METHODS TTTS placentas treated with laser at the Leiden University Medical Center and consecutively examined at our center be- tween June 1, 2002, and Aug. 1, 2008, were included in this study. Leiden Uni- versity Medical Center is the national re- ferral center for in utero management of TTTS in The Netherlands. Part of the placental data in this study was included in a previous report on RA. 4 We ex- cluded TTTS cases with intrauterine fetal demise (because of placental macera- tion) and TTTS cases treated with an al- ternative laser technique that comprises coagulation of the placental surface along the entire vascular equator. Dam- aged placentas were excluded if deterio- ration was too extensive to allow ade- quate and complete injection study. Furthermore, TTTS cases in which laser surgery was interrupted because of poor visibility or other reasons, were also ex- cluded. Diagnosis of TTTS was based on internationally accepted standardized antenatal ultrasound criteria. 6 Placental injection with colored dye was performed to determine the localiza- tion, size, type, and number of RA. De- tails on the technique used for placental injection have been described previ- ously. 4 Digital pictures of the placentas were taken perpendicularly to the pla- centa. We measured the length of the vascular equator on the digital picture of the placenta using Image Tool for Win- dows version 3.0 (Image Tool, San Anto- nio, TX). We measured the distance be- tween each RA and the margin of the placenta and expressed this distance as a percentage of the distance between mar- gin and center of the vascular equator. We divided the distance between margin and center of the vascular equator into 5 equal segments (of 20%). From the Division of Neonatology, Department of Pediatrics (Dr Lopriore), and the Division of Fetal Medicine, Department of Obstetrics (Drs Slaghekke, Middeldorp, Klumper, Oepkes, and Vandenbussche), Leiden University Medical Centre, Leiden, The Netherlands. Received Aug. 15, 2008; revised Nov. 7, 2008; accepted Jan. 13, 2009. Reprints not available from the authors. 0002-9378/$36.00 © 2009 Mosby, Inc. All rights reserved. doi: 10.1016/j.ajog.2009.01.010 Research www. AJOG.org MONTH 2009 American Journal of Obstetrics & Gynecology 1.e1 ARTICLE IN PRESS