EDITORThe finding of a mixture of both 46,XX and 46,XY cells in amniotic fluid culture has been frequently described. In the great majority of cases, the finding is followed by the birth of a normal male infant, leading to a consensus that the finding is the result of contamination with maternal cells in a normal male fetus. There are, however, several other possible explanations for a 46,XX/46,XY karyotype at amniocentesis. These include the presence of cells from an undiagnosed twin pregnancy, cross contamination in the laboratory, the presence of cells from a "vanished" male twin, and true fetal chimerism.¹ Reassuringly, all previously reported cases where 46,XX/46,XY has been found at amniocentesis have resulted in the birth of a child with a normal genital phenotype.

We present a case where a 46,XX/46,XY karyotype was found on amniocentesis. This resulted in the birth of an infant with true chimerism and . . . [Full text of this article]