[On the position of the human foetus and the probability of spontaneous change in position during pregnancy (author's transl)].

Since ultrasonic examinations became routine practice in pregnancy rather often breech presentations are being found in the course of pregnancy. The amounts of breech, vertex presentation and cross position in the course of pregnancy are shown in a curve which is made from 2.240 single measurements. There are significant differences between primiparae and multiparae as to the frequency of breech and vertex presentation. The analysis of all repeated determinations of fetal presentations allows predications about the probability of changing of a breech into a vertex presentation and vice versa in a determined week of pregnancy. For example the probability of the turning of a breech presentation into a vertex presentation is 44.6% in the 29th week post menstruation, 23.2% in the 33rd week post menstruation. From the 37th week onwards the fetus won't turn any more into the vertex presentation. A vertex presentation, for example in the 29th week post menstruation changes into a breech presentation with a probability of only 0.55%. From the 33rd week onwards a turn into a breech presentation is no longer to be expected. A diagram for the probabilities of the fetal presentations' turnings into the opposite presentations is given for the 13.-40. week post menstruation, from which the patient can immediately be informed about the individual chance. The turn into the vertex presentation is the most common one and seems to be the physiologic one. This turn occurs more or less constantly, not abruptly.