Chorionic plate vascular anatomy determines the efficacy of amnioreduction therapy for twin-twin transfusion syndrome.

The objective of the study was to determine whether vascular anatomy of monochorial placenta influences the therapeutic efficacy of serial amnioreduction in chronic mid-trimester twin-twin transfusion syndrome (TTTS). Twenty-six consecutive monochorial pregnancies complicated by TTTS and treated by serial amnioreduction were studied. The placental anastomoses were delineated postnatally by perfusion studies. Amniotic fluid index, amniotic fluid pressure, number of amnioreductions, interval between amnioreduction, and neonatal outcome were correlated with the presence or absence of superficial anastomotic channels and type of cord insertion. Placentae were divided into two groups according to the presence (n = 9) and absence (n = 14) of superficial anastomosis. Gestational age at diagnosis, delivery, percentage discordance in estimated birth weight were comparable in the two groups. The amniotic fluid index, liquor volume removed, and amniotic pressure at first amnioreduction were also comparable between groups. In the group without superficial arterio-arterial/veno-venous (AA/VV) anastomoses, amnioreduction was required more often (P < 0.05). Perinatal mortality in terms of intrauterine deaths (IUD) and neonatal death was more common in the group without AA/VV anastomotic channels (P < 0.05). There was no difference in incidence of velamentous/marginal cord insertion between the two groups. TTTS lacking superficial AA or VV anastomosis are more likely to require frequent amnioreduction and are associated with increased perinatal mortality and morbidity, whereas the presence of such shunts was associated with increased therapeutic efficacy of amnioreduction and a more favourable prognosis.