(1129) Let’s talk about twin survival after fetal therapy...the same way

Objective: To understand the various measurement constructs that can be used describe twin outcomes after fetal therapy and demonstrate how these methods can represent the same data differently.

Study Design: We evaluated all patients who underwent fetoscopic laser for twin to twin transfusion syndrome (TTTS) from 2014 to 2023 using commonly described outcome measures. Double twin survival (DS) is the percentage of pregnant patients who have two surviving twins. At Least One Survivor (ALOS) describes the sum of the percentage of pregnant patients with DS plus the percentage of those with a single survivor (SS). Perinatal survival (PS) considers each twin as a separate patient and potential survivor which is DS x2 + SS x 1 / all patients x 2. We compared DS to ALOS at the time of birth within our own cohort using Chi squared analysis. We also calculated the PS at birth for the same cohort.

Results: 408 patients underwent laser surgery for TTTS. The median gestational age at birth was 32.3 [29.2-34.2] weeks. 314/408 (77%) had double survival. An additional 65 (17.2%) patients had SS therefore 379/408 (93%) had ALOS which was statistically different from DS, p< 0.001. Perinatal survival was 693/816 (85%).

Conclusion: Amongst a cohort of 408 consecutive patients undergoing laser surgery, birth survival could be described as 77% (double survival), 93% (at least one survivor), or 85% (perinatal survival). These findings emphasize the importance of previously stated goals to harmonize and understand outcome measures, as well as outcomes. We recommend DS and PS as the most useful survival measures as ALOS underemphasizes the significance of single fetal demise.