[Third circulation: twin transfusion syndrome].

The estimated incidence in the Netherlands of serious previable twin-to-twin transfusion syndrome is 50-100 cases per year. The polyhydramnion-oligohydramnion sequence is the most prominent feature. Prognosis without treatment is dismal: previable preterm birth. Risk of serious morbidity in the surviving twin in case of foetal demise of the other is impressive. Once the diagnosis of monochorionicity has been made in the first trimester, detailed ultrasound examination is mandatory for early recognition of the development of the syndrome, as therapeutic options exist. Therapeutic options include piercing of the intertwin membrane, repeated amniocenteses or laser occlusion of the chorionic vasculature. In seven Dutch centres over three years time 61 cases were identified: 36 needed intervention; 63 (of the 122) children survived, 10 with longterm morbidity.