Objective: Twin-twin transfusion syndrome complicates up to 15% of monochorionic diamniotic gestations. Current recommendations for sonographic surveillance in monochorionic diamniotic pregnancies for detection of twin-twin transfusion syndrome vary. Our objective was to determine an appropriate frequency of sonographic surveillance to optimize detection of twin-twin transfusion syndrome in monochorionic diamniotic gestations.
Methods: A retrospective cohort analysis of all nonanomalous monochorionic diamniotic twins delivered at the University of North Carolina over a 9-year period was performed. The rate and gestational age of twin-twin transfusion syndrome onset were calculated. The time to the diagnosis of twin-twin transfusion syndrome was evaluated by a Kaplan-Meier survival curve; clinical factors at initial sonography were examined for their use in prediction of twin-twin transfusion syndrome.
Results: Of the 577 twin deliveries, 145 (25%) were monochorionic diamniotic and included for analysis. The rate of twin-twin transfusion syndrome was 17.93% (n = 26). The mean frequency of surveillance ± SD before diagnosis of twin-twin transfusion syndrome was 3.1 ± 2.1 weeks. The mean gestational age at diagnosis of twin-twin transfusion syndrome was 21.3 ± 3.4 weeks (range, 15-29 weeks). Both a discordant maximum vertical amniotic fluid pocket (>65% difference) and a discordant estimated fetal weight (>25% difference) at initial sonography showed a significantly shorter time to diagnosis of twin-twin transfusion syndrome (P < .0001).
Conclusions: Evaluation for twin-twin transfusion syndrome should begin in the second trimester. Weekly surveillance for those pregnancies with estimated fetal weight or maximum vertical pocket discordance is recommended. For those with a concordant estimated fetal weight and maximum vertical pocket, sonographic evaluation every 2 weeks is warranted to 28 to 30 weeks. After that, development of twin-twin transfusion syndrome is less likely, and a different paradigm of antenatal testing may be reasonable.