[Cytogenic anomalies and placental function].

Over the past few years growing knowledge of placental cytogenetics has led to the surprising observation that the chromosomal constitution of the placenta is not always identical to that of its fetus. This information comes primarily from three sources: analyses of chorionic villi obtained by choriocentesis (chorionic villus sampling); studies of abortions, particularly spontaneous ones; and analyses of extrafetal tissues performed following dubious prenatal diagnoses, or to investigate fetal pathologies such as intrauterine growth retardation. Our personal data and those reviewed in this article allow the conclusion that chromosomal aberrations, particularly in the mosaic state, are frequent in the placenta, and that at least some of these have less severe consequences when present in extrafetal tissues than when present in the fetus itself. The types of chromosomal errors observed differ according to the method of ascertainment, in spontaneous abortions for example as compared to pregnancies developing as far as the third trimester. The presence of a partially aneuploid placenta may be compatible with a continuing pregnancy, but be associated with problems such as inadequate fetal growth.