Fetal oxygen pulse oximetry: Preliminary data

The monitoring of fetal oxygen saturation (Sat O2) has been conceived to improve the surveillance of fetal conditions as a complement to FUR tracing (CTG). We have tested this method in our Institute in pregnant women, in order to validate the efficacy of pulse oxymetry. Normal term pregnancies were considered with the following inclusion criteria: at least three ultrasound scans in pregnancy for the confirmation of gestational age and placental situation, spontaneous labor and not assuming medicines able to influence the results of the analysis.

The average of the gestational age at birth has been of 40.3 ±1.0 (39-42 weeks), the average of the neonatal weight has been of 3468 ± 163 g. We have used for this study the fetal oxygen monitor OBS-500 (OB Scientific, Inc.), a compact pulse oxymetry device that appraises in contemporary the signal of the Sat O2 and the fetal cardiac frequency by means of a flexible sensor (OBS-900) situated on the shoulder of the fetus during labor. Umbilical cord blood sampling was obtained at birth after double clamping and before the first neonatal breath and subsequently performed the umbilical blood gas analysis (UBGA) of the artery and the umbilical vein.
We have inserted the probe to laboring women, when the cervix showed a dilation between 4 and 8 cm (average 6.6 ± 2.2 cm). In one case the probe has been inserted with entire membranes, under ultrasound guide (for checking placental situation). The average of the umbilical artery pH has been of 7.28 ± 0.06, and of the umbilical artery pO2 15.4 ± 3-4 mmHg. The average of the values of Sat O2 to 5, 10 and 15 minutes from birth were 50.0, 55.0 and 51.1 respectively. The median of Apgar scores to 1 and 5 min has been respectively 8 and 9.
From our data itemerges that a value of Sat O2 > 50 corresponds to an Apgar score and to UBGA values at birth within normality.

These are preliminary results to ascertain the reliability of the method in one cluster of normal pregnancies at term. A harvest of cases is in progress including alterations of CTG tracing in labor, with the aim to evaluate the utility of pulse oxymetry in the decision of "timing" and modalities of birth.