Evaluation of fetal oxygen saturation (SpO_2) during labor and effects of maternal oxygen administration on fetal SpO_2

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The purposes of study were to develop a new reflectance pulse oximetry probe which enables us to measure fetal SpO_2 during labor continuously and non-invasively and to evaluate correlation between fetal heart rate (FHR) and fetal SpO_2. And effect of maternal oxygen administration to fetal SpO_2 was estimated.Patients and methods : 120 patients from 30 to 41 weeks were measured. The reflectance probe was adapted to the fetal forehead, on condition that uterine cervix was dilated more than 5cm with rupture of the bag with informed consent. Fetal SpO_2 and FHR was simultaneously monitored. Oxygen was administrated by a rate 5/min by nasal connula after obtained informed consent.Results : 1) The shoe-horn typed reflectance probe, 10mm between LED and sensor, was developed. 2) Good correlation between fetal SpO_2 just before birth and umbilical arterial blood SaO_2 was confirmed (y=0.97_X-7.28). 3) Fetal SpO_2 at cervical os 5-7cm dilated was 56<plus-minus>13%. SpO_2 at 8-9cm dilated was 60<plus-minus>11%. SpO_2 in second phase was 56<plus-minus>11%. SpO_2 just before birth was 48<plus-minus>13% and significantly lower than other stages. 4) Early deceleration did not decrease fetal SpO_2.5) Late deceleration and severe variable deceleration significantly decreased fetal SpO_2.6) Maternal oxygen administration to lower fetal baseline SpO_2 (50%) led to significant increase of fetal SpO2.Conclusion : 1) Fetal SpO_2 during labor remains above 55% and decreased below 50% just before birth. 2) Late deceleration and severe variable deceleration decrease fetal SpO_2.3) Maternal oygen administration is effective for hypoxic fetuses to increase SpO_2. Reflectance pulse oximetry may have potential to be a good tool in monitoring fetal wellbeing during labor.