A mathematical model for evaluation of maternal cell contamination in cultured cells from spontaneous abortions: significance for cytogenetic analysis of prenatal selection factors.

OBJECTIVE To develop a mathematical model for more precise estimation of the incidence of chromosomal abnormalities and the sex ratio among spontaneous abortions masked by maternal cell contamination. DESIGN Retrospective analysis. SETTING Academic medical center. PATIENT(S) One hundred twelve samples of spontaneous abortion with a "46,XX" karyotype and 97 parents with aborted embryos. INTERVENTION(S) The presence of Y chromosome DNA in native tissues of "46,XX" spontaneous abortions was detected by amelogenin locus analysis. Detection of aneuploidies in noncultured tissues of "46,XX" abortions was performed by microsatellite DNA analysis and confirmed by fluorescence in situ hybridization. MAIN OUTCOME MEASURE(S) Accuracy of cytogenetic evaluation of spontaneous abortions. RESULT(S) Y chromosome DNA was revealed in 16% of the embryos with a "46,XX" karyotype. According to the mathematical model proposed, the frequency of chromosomal abnormalities in a sample of 478 abortions increased from 54.6% to 60.3%, and the sex ratio in embryos with normal karyotype changed from 0.66 to 1.02. The experimental validation of the model has shown that the observed and expected incidences of chromosomal abnormalities in "46,XX" abortions were in good agreement. CONCLUSION(S) Maternal cell contamination clearly affects the incidence of registered chromosomal abnormalities and the sex ratio in spontaneous abortions. Correction for maternal cell contamination should be taken into account before invoking biological explanations of sex ratio bias and might be useful to include in diagnostic reporting.