DNA ploidy determination of early molar pregnancies by image analysis: comparison to histologic classification

To improve histologic diagnosis of molar pregnancies, updated guidelines have been proposed recently. These guidelines take into account that less developed molar gestations differ from their fully developed counterparts.

To test the validity of these criteria by correlating histologic diagnosis with ploidy determination accomplished by means of image analysis.

Fifty archival cases of early molar pregnancy were reclassified according to the new criteria. The diagnosis had to be changed from partial to complete hydatidiform mole (PM to CM, respectively) in 9 cases and from CM to PM in 4 cases. DNA image cytometry could be performed in 40 cases (CM, n = 21; PM, n = 19).

There was 100% agreement between histologic diagnosis and a diploid or polyploid histogram in CM and 79% agreement between triploidy and PM, when the updated diagnostic criteria were used. This represents an improvement compared with diagnoses made with former criteria. Nevertheless, problems of correct classification remain: In 3 cases classified as PMs, fetal remnants were accompanied by the histologic appearance of a CM. These 3 cases could represent either a true embryonic development in CM or a twin gestation with one normal pregnancy and one mole, or they could belong to a (very rare) third type of mole. All of them show the same risk of persistent trophoblastic disease observed in classic CM.

As the groups at risk for developing persistent trophoblastic disease can be identified by their DNA histograms, ploidy analysis would be desirable in addition to histologic examination.