A case of a hydatidiform mole with a surviving coexistent fetus follow
ing in-vitro fertilization and embryo transfer is reported. The diagno
sis was established at 12 weeks gestation and pregnancy was maintained
until 31 weeks, during which time transient hyperthyroidism and lung
metastasis developed. No difference was observed in pronucleus formati
on and early embryonic development between the two embryos, which resu
lted in a complete mole and a normal fetus. DNA fingerprint analysis,
karyotype analysis and histopathological examination confirmed that th
e pregnancy was a twin of a complete mole and a normal conception. DNA
fingerprint analysis was performed with a single-locus probe cocktail
. All DNA bands from the tumour were of paternal origin, and the bands
from the placenta were of paternal and maternal origin.