[Intrauterine growth retardation associated with a mosaic trisomy 20 limited to the placenta. A case report].

When an amniocentesis was performed to determine fetal age, the karyotype was found to be a trisomy-20 mosaic, which could not be confirmed at birth on peripheral blood but which was confirmed at the cytogenetic examination of the placenta. Fetal growth impairment occurred. Mosaic trisomy in the placenta alone is known to affect fetal development. Normally, lethal, mosaic trisomy found during antenatal diagnosis in a viable fetus with no detectable malformation suggests an extra-embryo anomaly. The risk of spontaneous abortion and fetal growth retardation is however increased making strict echographic surveillance essential in these pregnancies.