[Twin pregnancy combining a hydatidiform mole and a normal ovum]

It is rare for a twin pregnancy to consist of a normally growing fetus and a hydatidiform mole. A differential diagnosis between a partial mole and a degenerating fibroid together with a normal pregnancy has to be made. This can be made using ultrasound pictures but also using cultures from trophoblast samples, or cultures from amniotic cells obtained by amniocentesis. These will eliminate the possibility of the triploidy by showing that there is a normal caryotype present. The complications and the risk of degeneration are the same as with a plain hydatiform mole. The uterus has to be evacuated and a follow-up has to be carried out to screen for trophoblastic proliferation.