[Twin pregnancy with severe skull malformation of one twin]

If, in twin pregnancy, one twin shows severe malformation, the question arises as to how the other twin can remain unaffected. For the purpose of ensuring the diagnosis in case of suspected neural tube defect, the main diagnostic tools are sonography, biochemical methods of alpha-fetoprotein determination and acetyl cholinesterase activity, as well as cell-morphological identification of so-called "rapidly adhering cells". Parents and obstetricians face a difficult decision when confronted by the possibilities of maintaining pregnancy or of induced abortion after diagnosis of a malformed and a healthy twin. The case of a severe discordant cranial malformation is described on the basis of a case report. The diagnostic and therapeutic problems are discussed.