Twin-twin transfusion syndrome.

Twin-twin transfusion syndrome (TTTS) is a condition unique to monochorionic pregnancies, although very few case reports described the syndrome in dichorionic placentas. The aetiology of TTTS relies in the presence of at least 1 arterio-venous placental anastomosis, through which unequal blood exchange from one twin (donor) to the co-twin (recipient) occurs. The diagnosis of TTTS relies on the sonographic detection of oligohydramnios in the donor's sac and polyhydramnios in the recipient's sac in the second trimester, although signs of TTTS are present since the first trimester. Treatment options for TTTS include serial amnioreduction, septostomy, selective feticide of the apparently sick twin, and selective photocoagulation of placental vessels (SLPCV). Because of the growing evidence that SLPCV is the most efficacious therapy compared to amnioreduction with/without septostomy, the authors reviewed in details the effects of SLPCV on fetal growth and circulation. The authors further explore literature with regard to the prognostic factors. Finally, because Quintero staging system is actually under debate, they discuss the most recent findings on this topic and propose a new staging system to assess severity of TTTS at presentation (Rossi staging system). New topics for future research, which would probably further clarify the natural history of TTTS, are also proposed.