A Reappraisal of the Incidence of Placental Hydatidiform Mole Using Selective Molecular Genotyping.

Objective Reports on the incidence of hydatidiform mole (HM) have varied depending on study population and methodology. This institutional-based study was undertaken to identify the incidence of HM in a modern obstetric practice using advanced laboratory diagnostic techniques. Methods A retrospective review of consecutive hospital cases of HM was conducted for a 27-month period. Pathologic diagnoses of partial mole (PM) and complete mole (CM) were based on histopathologic assessment and selective use of p57 immunohistochemistry and molecular genotyping (MG) using formalin-fixed paraffin-embedded tissues. Results During the study period, 14,944 obstetric deliveries took place at our institution. Forty-nine cases of HM (18 CMs, 31 PMs) were identified. Histopathology with the selective use of p57 immunohistochemistry was used in 25 of 49 HMs (18 CMs, 7 PMs). Histopathologic features were equivocal in the remaining cases (24/49 cases), and adjunctive MG was performed; all were PMs. The incidence of HM was 3.3/1000 deliveries. Partial mole was more prevalent with a CM (PM ratio, 1:1.72). Conclusions Our observed incidence of HM is greater than previous studies and is attributable to improved detection of PM cases. Molecular genotyping and cytogenetic evidence indicate that CM is almost half as common as PM. This ratio may be useful in benchmarking laboratory diagnosis and HM registries.