Diagnostic use of cordocentesis in twin pregnancy.

We performed percutaneous umbilical blood sampling, under ultrasound guidance, in both twins of 11 twin pregnancies in whom twin-to-twin transfusion syndrome was suspected. Chorionicity and the presence of placental vascular anastomoses were assessed postnatally. The hemoglobin concentration, hematocrit and other biochemical variables in fetal blood were evaluated in both twins. The mean hemoglobin difference between the large and small twins was 4.8 g/dl (range 1.8-8.1 g/dl) in 5 monochorionic discordant twin pairs, and 1.2 g/dl in a monochorionic twin pair without discordancy. Hemoglobin values did not differ between dichorionic twins. The mean hematocrit difference between monochorionic discordant twins was 18.3%. In dichorionic discordant twins, the inter-twin hematocrit difference was very small. Total protein and albumin were normal in all twins.