Auditory evoked responses in the human fetus. II. Modifications observed during labor.

The author presents his observations made on the behavior of an auditory evoked response of the human fetus during labor, elicited by a standardized sound stimulus at 1500 cycles/second. The method was applied to 233 women during labor and the pattern of responses evoked by sound stimulation was studied in all clinical conditions present in this high-risk population. A fair number of observations was made on vigorous/depressed newborns by Apgar rating, in the presence of definite cardiotocographic signals of fetal distress, in cases of intact or ruptured membranes, in cephalo-pelvic disproportion, in the presence of maternal risk factors, in cases of cord entaglement, in cases of meconium present in amniotic fluid, in intra-uterine growth retardation, hypertensive disease of pregnancy, and in familial and class A diabetes. A significant decrease in the response to sound stimulation was observed in cases of fetuses born in a depressed condition, after more than 2 hours following membrane rupture, in the presence of maternal obstetric risk factors, and in cases of hypertension in pregnancy. Women with intra-uterine growth retardation and cephalo-pelvic disproportion presented smaller changes and in cases of umbilical cord entaglement, presence of meconium in amniotic fluid and with history of familial or class A diabetes, no differences in the patterns of responses to sound stimulation as compared with normal could be observed. The author observed a good correlation between the auditory evoked response and fetal conditions during the course of labor and suggests that this method should be further developed as a simple method of evaluating the cerebral function of the unborn human fetus. In the first published part of this study (19) we described the modifications in the auditory evoked response of the human fetus caused by the progress of labor. A closer scrutiny of our data revealed the influence of several other factors acting upon the pattern of fetal response to sound stimulation. The present paper describes studies on those factors influencing the behavior of the human fetus following sound stimulation.