Abnormal conceptus in which there is coexistence of a hydatidiform mole with a fetus; caused by triploidy. Not as dangerous as a molar pregnancy without a fetus (see hydatidiform mole, complete), but medical follow-up is still necessary.

A state of 69 chromosomes, or three times the haploid number, most commonly caused by fertilisation of the egg with two sperm; the embryo that results can develop as far as a fetus, but is doomed to miscarry. The trophoblast of the placenta often undergoes partial changes of a hydatidiform mole. The noun form for this adjective is triploidy (the state of being triploid).