Table 1

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

	Mechanism	Fetal karyotype	Origin of X chromosomes	Pregnancy outcome (phenotype)	Estimated frequency
1	Maternal contamination	46,XY	All maternal	Normal male	1–2/1000
2	Twin pregnancy	46,XX and 46,XY	Maternal and paternal	Normal female and normal male twins	Rare (2 cases reported)
3	Male cells of unknown origin (possible “vanishing twin”)	46,XX^1-150	Maternal and paternal	Normal female	Rare (3 cases reported)
4	Cross contamination in laboratory	46,XX or 46,XY	Non-parental	Normal male or normal female	Unknown
5	True fetal chimerism	46,XX/46,XY	Maternal and paternal	True hermaphrodite/ normal male/ normal female	Rare (2 cases reported)
6	Parthenogenetic chimera	46,XX/46,XY	All maternal	Phenotypic uncertain: possible physical/intellectual compromise	Never reported at prenatal diagnosis

↵1-150 The presence of male cells in the fetus that were not detectable after delivery cannot be excluded.