Sex chromosome mosaicism not detected at amniocentesis.

Amniocentesis was performed because of a fetal abdominal wall defect, and a 45,X karyotype was obtained. A near-normal male infant with no features of Turner syndrome was delivered. The karyotype of the infant was 45,X/46,X,dic(Y)(q11), with each of the cell lines present in approximately 50 per cent of the lymphocytes and fibroblasts examined.