Table 1

Mechanism and outcome of 46,XX/46,XY at amniocentesis

MechanismFetal karyotypeOrigin of X chromosomesPregnancy outcome (phenotype)Estimated frequency
1Maternal contamination46,XYAll maternalNormal male1–2/1000
2Twin pregnancy46,XX and 46,XYMaternal and paternalNormal female and normal male twinsRare (2 cases reported)
3Male cells of unknown origin (possible “vanishing twin”)46,XX1-150 Maternal and paternalNormal femaleRare (3 cases reported)
4Cross contamination in laboratory46,XX or 46,XYNon-parentalNormal male or normal femaleUnknown
5True fetal chimerism46,XX/46,XYMaternal and paternalTrue hermaphrodite/ normal male/ normal femaleRare (2 cases reported)
6Parthenogenetic chimera46,XX/46,XYAll maternalPhenotypic uncertain: possible physical/intellectual compromiseNever reported at prenatal diagnosis
  • 1-150 The presence of male cells in the fetus that were not detectable after delivery cannot be excluded.