The effect of confined placental mosaicism on development of the human aneuploid conceptus.

The rate of meiotic errors in gametogenesis is high, resulting in approximately 30% of cleaving embryos with chromosomal defect. In addition, mitotic errors occur commonly in chromosomally normal and abnormal embryos. The most likely outcome of the mitotic error is CPM. Mitotic mutation in trisomic blastocysts may lead to diploid/trisomic trophoblast with intrauterine survival of the trisomic fetus or may result in a diploid fetus supported by a trisomic placenta. The outcome of pregnancies with a trisomic placenta and diploid fetus largely depends on the specific chromosome involved and on the presence or absence of uniparental disomy in the fetus.