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182: Preoperative ultrasound prediction of essential landmarks for fetoscopic laser coagulation of placental vascular anastomoses

      Objective

      Successful fetoscopic laser occlusion (FLOC) treatment of twin twin transfusion (TTTS) hinges on selecting a uterine entry that safely allows complete visualization of all anastomoses along the vascular equator (VE). We hypothesized that pre-operative ultrasound of the donor lie, placental cord insertions and size discordance can predict the orientation and position of the intertwin membrane and VE (Figure) to allow successful FLOC.
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      Study Design

      The orientation of the key landmarks was prospectively and independently documented by 3 surgeons prior to FLOC. Following FLOC the intraoperative findings were compared to the preoperative prediction. Correct identification of basic and specific membrane, VE, VE to membrane orientation and inadvertent anterior septostomy was computed and related to case characteristics, surgeon experience and intraoperative outcome.

      Results

      In a 3 month period 59 assessments were performed prior to 24 FLOC surgeries (10 Quintero stages 1&2, 14 stages 3&4; median gestational age 18.8 weeks (16.3-25.6); median fluid pockets 10 cm (8.1-22) and 1 cm (0-2) in recipient and donor, respectively). The maternal body mass index was 28 kg/m2 (17.6-62.7). Basic membrane and equator orientation were correctly predicted in 52 (88.1%) and 51 (86.4%) of assessments and specific prediction was correct in 40 (66%) and 31 (52.5%), respectively. The basic relationship between the membrane and equator was correctly predicted in 45 (76.3%) of assessments but their specific relationship prediction was correct in only 19 (32.2%). There were 2 anterior septostomies of the intertwin membrane. The predicted entry provided adequate visualization of the vascular equator allowing complete equatorial dichorionization in 87.5% (n=21). Incomplete equator visualization was due to extensive anterior placenta which would not have been circumvented by a different entry site. The prediction accuracy was independent of surgeon experience, placental location, amniotic fluid volume. High body mass index (r2 0.36, p=0.001) was the only factor that negatively impacted optimal preoperative assessment.

      Conclusion

      We present a simple ultrasound technique that allows reproducible and consistent preoperative prediction of key anatomic landmarks for successful FLOC treatment of TTTS independent of multiple potential confounders.