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359: Monochorionic diamniotic twin pregnancy: surveillance frequency for detection of twin-twin transfusion syndrome

      Objective

      Twin-twin transfusion syndrome (TTTS) is a serious complication of monochorionic diamniotic (MCDA) gestations. Current recommendations for ultrasound (US) surveillance in MCDA pregnancies for detection of TTTS vary. Our objective was to determine an appropriate interval to identify TTTS in MCDA twin pregnancies.

      Study Design

      Retrospective cohort analysis of all non-anomalous MCDA twins over a 9-year period. Rates and gestational age (GA) of onset of TTTS were calculated. Time to the diagnosis of TTTS was evaluated by Kaplan-Meier survival curve (Figure 1).
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      Figure 1Kaplan-Meier survival curve to dx of TTTS

      Results

      Of the 542 twin deliveries, 145 (27%) were MCDA. The rate of TTTS was 17.93% (N=26). The mean GA of diagnosis of TTTS was 21 ± 3.4 weeks (range 15 to 29 weeks). Both discordant MVP (>65% difference) and discordant EFW (> 25% difference) at initial US demonstrated significantly shorter interval to diagnosis of TTTS (log rank test p<0.0001).

      Conclusion

      Evaluation for TTTS should begin in the second trimester. Weekly surveillance for those pregnancies with EFW discordance and MVP discordance is recommended. Evaluation every 2 weeks is warranted to 28 weeks. After that, development of TTTS is unlikely, and serial examinations every 3-4 weeks is appropriate. Confirmation with larger sample sizes and incorporation of first trimester CRL measurements can further clarify ideal fetal testing schedule.