Complete hydatidiform mole and normal live birth: a novel case of confined placental mosaicism: case report

Hydatidiform molar change, characterized by abnormal fetoplacental development and placental villous trophoblast hyperplasia, results from genetically abnormal conception, in which there is an excess of paternally derived genetic material. The majority of pregnancies in which molar change has been reported in association with a live fetus represent dizygotic twin pregnancies in which one fertilization results in a complete hydatidiform mole (CM) and the other a normal co-twin. In such cases, there is usually a clear distinction, both sonographically and pathologically, between the molar and non-molar regions of the placenta. We present a singleton pregnancy, with diffuse placental molar change detected prenatally, which resulted in a chromosomally and phenotypically normal female infant at term. Pathological examination revealed the presence of intermixed populations of morphologically normal chorionic villi and villi with the characteristics of CM. Studies of genetic polymorphisms demonstrated that the CM, normal villi and fetus were all derived from the same sperm; the fetus was diploid and biparental whereas the areas of pathological CM were androgenetic and monospermic. We believe this represents the first well-documented case of apparent confined placental mosaicism involving CM and a coexisting normal fetus, which has presumably arisen following mitotic abnormalities in the early post-fertilization period.