Predictive agreement between the fetal arterial oxygen saturation and fetal scalp pH: results of the German...

To discuss and substantiate the 30% critical threshold of fetal arterial oxygen saturation and to complete the puzzle with low fetal arterial oxygen saturation and low scalp pH data, scalp samples have been performed while fetal arterial oxygen saturation registration during labor was in place and while the saturation was < or = 30%.

Between 1993 and 1996, 46 term fetuses during active labor had parallel arterial oxygen saturation registration by pulse oximetry combined with cardiotocograph. They include patients in whom the saturation was < or = 30% for at least 10 minutes. In these cases scalp pH sample values have been obtained simultaneously. Outcome data, Apgar scores, cord gases, and whether the infants were transferred to the neonatal intensive care unit have been examined. Compared with this, there were other cases during labor that had also parallel fetal arterial oxygen saturation and cardiotocographic registration, where the saturation was > 30%. Also in these cases scalp pH was determined to support and demonstrate the predictive value of fetal arterial oxygen saturation for scalp pH, especially in the low ranges. All 46 fetuses were evaluated during periods of nonreassuring cardiotocograph with Nellcor N-400 Fetal Oxygen Saturation Monitoring Systems and FS 14 B sensors in a multicenter study involving three German obstetric centers. Receiver operating characteristic analysis was done on all raw data, as well as the receiver operating characteristic curve from the preceding analysis.

These data validate the critical threshold of 30% fetal arterial oxygen saturation and show an extremely good separation of "good" versus "bad" at a fetal arterial oxygen saturation of 30%, especially when seen in conjunction with data points that are > 7.20. Data at < or = 7.20 scalp pH and < 30% fetal arterial oxygen saturation can be a big help in calculating the sensitivity and specificity of fetal arterial oxygen saturation in predicting neonatal outcome (e.g., Apgar score, cord pH).

Low fetal arterial oxygen saturation data of < 30% for at least 10 minutes or longer correlate significantly with low scalp pH values and have a predictive value concerning fetal outcome.