Partial hydatidiform mole is a type of molar pregnancy. Its etiology consists of the fertilization of the same ovum with two spermatozoa, giving rise to a triploid embryo. This type of molar pregnancy can also be caused by the fertilization of an egg with a diploid spermatozoon, so it is altered and has 46 chromosomes.
The embryo's karyotype is made up of 69 chromosomes, instead of the normal 46. This embryo is not compatible with life and miscarriage usually occurs.