[Fetal oxygen saturation in suspected hypoxia and the normal cardiotocogram (CTG). A prospective study for validating pulse oximetry in the fetus].

During a clinical study 70 women in labour were monitored with fetal pulse oximetry. The oxisensor (FS 10) was positioned between fetal cheek and the uterine wall at a cervical dilatation of 2 cm or more. The advantage of the method is its minimal invasive character and the continuous monitoring of oxygen saturation. The pulse oximeter (N 400, Nellcor) had been blinded for the investigation following criteria met by FDA, so that the investigator could not read the saturation values. Preliminary results of more than 120 hours of monitoring intervals of 10 seconds show the following saturation values (median): 55% under normal CTG (10. perc. 36%, 90. perc. 73%), 42% during episodes of variable decelerations (10. perc. 22%, 90. perc. 63%), 53% during episodes of early decelerations (10. perc. 39%, 90. perc. 74%). Due to pathological fetal heart rate patterns 42 fetal blood analysis were performed. Because of these spectrophotometric saturation measurements (ABL 330, OSM 3, Radiometer) the deviation of the two methods could be calculated. The values of pulse oximetry were 5% higher than those of spectrophotometry. Correlation of both methods was r = 0.64.