Ploidy analysis by flow cytometry and fluorescence in situ hybridization in hydropic placentas and gestational trophoblastic disease.

Placentas with hydropic change may be hydropic degeneration (HD) or gestational trophoblastic disease (GTD), partial (PM) or complete (CM) hydatidiform mole. The separation of HD from PM and PM from CM by histological findings may be problematic in some cases and can be clarified with ploidy analysis. Fluorescence in situ hybridization (FISH) using a probe to chromosome 7 (D7Z1) was applied to tissue cut from paraffin blocks from 10 histologically representative cases each of HD, PM, and CM on which ploidy had been previously confirmed by flow cytometry from paraffin embedded tissue. Villous stromal cells and nonproliferative trophoblast were examined for number of signals/cell and percentage of cells/placenta with three hybridization signals. The mean number of hybridization signals/cell was HD 1.14; PM 1.79; and CM 1.17, with statistical significance between HD and PM (P < .0001), and PM and CM (P < .0001). The mean percentage of cells/placenta with three hybridization signals was HD 1.10%, PM 23.1%, and CM 2.11%, with statistical significance between HD and PM (P < .0001), and PM and CM (P < .0001). In addition, there was no overlap in the mean percentage of cells with three hybridization signals between HD and PM, and PM and CM. Chromosome 2 probe (D2Z1) was applied to tissues that had three chromosome 7 signals to exclude trisomy, and in all cases three signals were present confirming triploidy in PM. FISH can identify diploid and triploid hydropic placentas in paraffin-embedded tissue to assist in differentiating HD from PM, and PM from CM.