Cerebral hemoglobin concentration and oxygen saturation measured by intensity modulated optical spectroscopy in the human fetus during labor

Aims: To quantify hemoglobin concentration and oxygen saturation in the human fetal brain using intensity modulated optical spectroscopy during labor. Methods: A specially designed probe was applied to the fetal scalp in 20 women during uncomplicated labor at term. Optical fibres transmitted near infra-red light to and from an intensity modulated optical spectrometer (IMOS), which detected changes in the optical parameters of the infra-red light source. Using novel off-line analytic techniques, these changes were converted into absolute measurements of oxyhemoglobin (HbO 2 ) and deoxyhemoglobin (Hb). Summing Hb and HbO 2 gives total hemoglobin concentration (HbT) and HbO 2 /HbT x 100% provided measurements of cerebral saturation (SmcO 2 ). Results: Of 20 fetuses studied, data from 10 fetuses were suitable for analysis. Over three consecutive uterine contractions, the mean (± SD) absolute cerebral concentrations of Hb and HbO 2 were 30+/-18 and 46+1-21 μmol/l, respectively. This gave a mean cerebral HbT of 77+/-29 μmol/l and a mean SmcO 2 of 59+/-12 %.In the other ten fetuses insufficient light was detected to allow chromophore quantification. Conclusion: These are the first absolute measurements of cerebral Hb and HbO 2 in human fetuses during labor. The values of total hemoglobin are similar to those obtained in neonates with hypoxia-ischemia and the measurements of fetal cerebral oxygen saturation are similar to nreviouslv nublished values.