[The placenta in trisomy in the last trimester of pregnancy].

18 cases of trisomies 13, 18, or 21 were diagnosed either by examining the caryotype or on clinical criteria. When the placenta was examined in 60% of cases there was a marked retardation of villous maturation with frequent persistence of embryonic forms of villi. The authors suggest that the failure of the villi to mature was often a reflection of pathology in the oocyte which started to show itself at the beginning of the pregnancy.