[Stress on the head of the fetus in spontaneous labor in relation to perinatal factors].

The pressure exerted on the fetal head during the second stage of labor was continuously measured in 42 spontaneous deliveries with a new instrument. The pressure values were correlated to various obstetric variables. Typically, the head pressure remained elevated beyond the end of the uterine contraction in primiparae, whereas it decreased simultaneously with the amniotic pressure in multiparae. On the average, the head pressure was higher in primiparae indicating, together with the longer lasting bearing down period, a higher resistance of the birth canal. Deliveries with pudendal block or peridural analgesia showed no differences, but these two groups differed in other factors which might have influenced the results. Infusion of oxytocin during the course of labor was associated with higher head pressure values that could not be deduced from the hormone administration per se, but from a higher resistance of the birth canal. Maternal age did not influence the head pressure. Within physiological limits, the head pressure was independent from the size of the child and the maternal pelvis.