Complete hydatidiform mole coexistent with a twin live fetus: clinical course of four cases with complete cytogenetic analysis.

Twin gestations can occur in which one twin is a normal gestation (46 chromosomes: 23 maternal and 23 paternal origin) and in which the other twin is a complete hydatidiform mole (46 chromosomes all of paternal origin). Case reports of four such combined pregnancies that presented to a single institution are provided. All cases had documentation of clinical information, cytogenetic analysis, and fetal and placental pathology. Three of the four pregnancies were terminated for medical indications despite information documenting the presence of a normal fetus. All three of these patients required subsequent chemotherapy. The fourth case was followed conservatively and resulted in the birth of a normal infant at 38 weeks gestation. We speculate that the factors that led to the need for termination of the pregnancy (aggressive growth of trophoblast) may predict the need for further therapy. A true assessment of the antenatal and malignant sequelae risks associated with these rare gestations awaits the collection of a larger series of patients.