A dichorionic twin pregnancy was diagnosed in a 26-year-old woman after first- and second-trimester ultrasounds identified a twin peak sign. However, at 23 weeks’ gestation, sonographic findings consistent with Quintero stage III donor twin-twin transfusion syndrome (TTTS) developed. After counseling on management options, the patient decided to proceed with diagnostic fetoscopy and selective laser photocoagulation of communication vessels if vascular communications were identified.
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Diagnostic fetoscopy revealed a midline “bridge” of placenta that contained 9 vascular communications. The middle portion of the dividing membranes appeared thin and translucent, which is typical of monochorionic-diamniotic twins; the lateral portions of the dividing membranes were thick and more opaque in appearance, consistent with dichorionic-diamniotic twins ( Figure 1 ). A distinct line demarcating the transition from monochorionicity to dichorionicity was visible in the dividing membranes ( Video Clip ). Selective laser photocoagulation of communication vessels was performed as previously described elsewhere. Of note: 2 placental vessels tunneled within the placenta and emerged remotely.
The patient delivered at 28 weeks’ gestation due to premature rupture of membranes followed by preterm labor. Gross examination of the placenta disclosed a hybrid monochorionic/dichorionic placenta ( Figure 2 ). Histological evaluation of the transitional zone in the dividing membranes confirmed the absence of intervening chorion within the monochorionic portion ( Figure 3 ). Placental injection studies revealed no residual patent anastomoses.