Confined placental mosaicism and intrauterine development.

Confined placental chromosomal mosaicism can be detected in 1-2% of pregnancies studied by chorionic villus sampling at 9-12 weeks of gestation. It is more commonly found in the cytotrophoblast than in placental connective tissue. Aneuploid conceptions are more likely to have confined chromosomal mosaicism than euploid ones. Although intrauterine survival of chromosomally abnormal embryos and fetuses appears to be significantly enhanced by placental mosaicism, the effect of placental mosaicism on chromosomally normal fetuses is variable and, at the present time, still unpredictable.