Objective: To identify a twin pregnancy consisting of a complete mole and coexistent fetus by means of molecular cytogenetics and DNA polymorphisms.
Study design: Seven highly polymorphic DNA markers were used to establish the androgenetic origin of a complete hydatidiform mole that coexisted with a normal 46,XY fetus. Cytogenetic analysis of mole nuclei was performed with centromeric probes, demonstrating a 46,XX constitution.
Results: Molar tissue was diploid with two X chromosomes, possibly due to chromosome doubling after monospermic fertilization of an ovum with inactivated or absent nucleus.
Conclusion: Although contamination with maternal tissue may be difficult to avoid, molecular markers provide the possibility of distinguishing between a complete hydatidiform mole and coexisting normal fetus versus a partial mole, with methods that can be performed antenatally. This distinction is important since in the first case up to 24% of fetuses described in the literature have been viable, and the risk of subsequent development of persistent trophoblastic tumor in patients with a complete mole and a coexisting fetus is considerably higher than in patients with a single, complete hydatidiform mole.