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Tetraploidy in Prenatal Diagnosis: “culture artifact” or clinical diagnosis?

In routine analysis of cultured CVS and amniotic fluid (AF) a few tetraploid cells are almost always observed. However, they are usually assumed to be due to culture artifact and are rarely documented in the laboratory report. In some CVS studies tetraploidy has retrospectively been reported as a “false positive” result. We present two cases which document the difficulty in interpreting tetraploidy.Case 1: AF was obtained at 40 weeks gestation from a fetus with multiple congenital anomalies. Interphase FISH analysis using probes for 13,18,21,X and Y was consistent with tetraploidy. Routine G banded analysis of cultured AF and fetal skin following delivery revealed only tetraploid metaphases. Congenital abnormalities in the infant were consistent with those previously reported in the literature.Case 2: CVS was performed at 12 weeks because of maternal age 39 and increased nuchal thickening. All 15 cells from long term culture were tetraploid while 5 cells from short term/direct preparation had a normal 46,XY karyotype. No tetraploid cells were found in cord blood following delivery while 4/30 metaphases from cultured umbilical cord were tetraploid. The infant's only congenital abnormality was a bicuspid dysplastic aortic valve with mild aortic stenosis.Conclusion: The clinical significance of mosaic and nonmosaic tetraploidy appears to be at least in part related to the type of tissue analyzed. The presence of nonmosaic tetraploid cells in uncultured amniotic fluid by interphase FISH appears to be a strong indicator of fetal abnormality. Mosaic diploidy/tetraploidy in CVS and cultured fibroblasts is of uncertain clinical significance.