638: Outcome of fetoscopic laser ablation for twin twin transfusion syndrome in relation to procedure details

Fetoscopic laser occlusion (FLOC) can provide definitive treatment for previable twin twin transfusion syndrome (TTTS). It was our aim to determine the relationship between procedure quality and outcome. All patients undergoing FLOC for TTTS had a standardized assessment of the procedure details (placental location, ability to visualize anastomoses, ease of coagulation (each graded 1-4), need for amnioinfusion, intraoperative complication, transamniotic laser, septosotomy, laser energy and duration were recorded). Twin survival, evidence of recurrence (twin anemia/polycythemia sequence (TAPS) or oligo/poly sequence (TOPS) was evaluated. Impact of individual procedural details and cumulative assessment as optimal/suboptimal was related to outcome. 71 twins and 1 triplet underwent FLOC for stage 1/2 (n=33, 46%) and stage 3/4 (n=39, 54.1%) TTTS at 20.6 weeks gestation (17.2-25.6). Overall procedure survival was 81.5% (62.2% with 2 survivors, 36.5 % with 1 survivor, one with no survivors). Survival was unrelated to procedure characteristics. Anterior placenta affected coagulation success in 8/32 procedures versus 1/41 with non-anterior placenta (p=0.004) and the procedure was more likely to be ”suboptimal” (18/32 versus 11/41, p=0.008). Inability to completely assess the whole vascular equator was associated with significant recurrence risk 6/15 (3 TAPS, 5 TOPS, all p<0.05). When coagulation was suboptimal overall risk for recurrence increased (4/9, p<0.05). No other procedure characteristics contributed to recurrence risk or rates of preterm membrane rupture and delivery. The ability to visualize the intertwin vascular equator is the key component to successful FLOC treatment for TTTS. Suboptimal coagulation due to tangential technique in anterior placenta or large vessel size are secondary contributors to treatment failure.