[Effects of spontaneous abortions on the frequency of births of twins].

The frequency of spontaneous abortion of one zygote after double ovulation-fertilization makes it possible to explain some of the main features of the dizygotic twinning rate, namely the sharp decrease of this rate at higher maternal ages after its regular increase up to 35 years, and also the secular tendancy of this rate to decrease, observed in many countries. The consequences of these findings are discussed, in particular those which are related to the etiology of spontaneous abortion and mongolism, and to the frequency of multiple ovulation.