In idiopathic thrombocytopenic purpura, the low risk of fetal bleeding in the perinatal period does not justify routine cordocentesis. Platelet counts of second newborns correlates well with that of their siblings. In neonatal alloimmune thrombocytopenia, the initial platelet count at cordocentesis in the second trimester is low in the next pregnancy. Weekly high doses of intravenous gammaglobulin to the mother results in a rise of fetal platelet count in approximately 70% of cases and may protect the fetus against intracranial haemorrhage in cases without significant platelet rise. With the exception of cases with a prior infant with spontaneous fetal intracranial haemorrhage, the use of diagnostic fetal blood sampling to confirm neonatal alloimmune thrombocytopenia is controversial.