Cytogenetic diagnosis of "normal 46,XX" karyotypes in spontaneous abortions frequently may be misleading.

Objective: To use the molecular identification of Y chromosome material in products of conception cytogenetically diagnosed as "46,XX" to confirm the occurrence of inaccurate cytogenetic test results most likely attributable to maternal cell contamination.

Methods: Retrospective analysis. Methods: Academic medical center. Methods: Thirty-four archival tissues from cases of spontaneous abortion with a "46,XX" karyotype based on cytogenetic analysis. Methods: Maternal and villus DNA were extracted from microdissected, formalin-fixed, paraffin-embedded archival tissues. The presence of the X and Y chromosomes was detected with the use of polymerase chain reaction assays and confirmed with fluorescence in situ hybridization. Methods: Accuracy of cytogenetic evaluation of products of conception.

Results: Four (29%) of 14 first trimester and 1 (5%) of 20 second trimester "46,XX" pregnancy losses contained Y chromosome-specific DNA and demonstrated a single X chromosome-specific allele by polymerase chain reaction analysis consistent with an "XY" karyotype. Fluorescence in situ hybridization was confirmatory in 4 of 5 samples that demonstrated single X and Y signals in villus cells.

Conclusions: Inaccuracy exists in the cytogenetic analysis of early products of conception that most likely is due to maternal cell contamination. In the absence of confirmatory testing, such as with a "DNA fingerprinting" assay, reports of a "46,XX" karyotype should be used cautiously in patient counseling and management.