[The placenta and trisomies 13, 18, 21].

In 30 cases of trisomies 13, 18 and 21, the placenta showed different lesions of hypotrophy, immaturity, hydrops, trophoblastic recurrences or cysts and mineralisation of the trophoblastic basal lamina. These are non specific lesions and can be observed in a variety of conditions, but their association is striking in most cases of trisomies. Different pathological patterns may thus evoke a trisomy, though that diagnosis can only be ascertained by chromosome analysis.