The use of intensity modulated optical spectroscopy to measure cerebral saturation and haemoglobin concentration in the human fetus during labour.

Background: Although intrapartum hypoxia-ischaemia is an important cause of death and permanent brain injury, current available methods for the detection of damaging fetal hypoxia are unsatisfactory and unreliable. Electronic fetal heart rate monitoring (EFM) is considered to be the "gold standard" for intrapartum fetal surveillance. However, monitoring of the fetal heart rate provides an indirect measure of fetal hypoxia and provides little indication of the adequacy of cerebral perfusion. Consequently, EFM has a false positive rate of 99.8% in the detection of fetuses that subsequently develop cerebral palsy. A direct consequence of the poor specificity of fetal heart rate monitoring is a high rate of unnecessary Caesarean sections with associated fetal and maternal morbidity. Most fetuses subjected to intrapartum hypoxia will be protected from brain injury by appropriate changes in cardiovascular distribution. It is the aim of fetal surveillance to detect the minority of fetuses in whom this response is absent and who are at risk of permanent brain injury. Intrapartum fetal pulse oximetry is a promising new method of fetal surveillance, enabling measurement of fetal arteriolar saturation but the technique provides no direct information on cerebral oxygen delivery. Intrapartum measurement of fetal cerebral saturation and changes in blood volume has been described using conventional near infrared spectroscopy (NIRS). However, the clinical relevance of these values may be limited. This is because these values are derived from changes in the concentrations of oxyhaemoglobin (HbCh) and deoxyhaemoglobin (Hb) from an arbitrary baseline. Furthermore, the contribution of artefact to NIRS measurements of Hb and HbC>2 changes, arising from possible changes in the geometry of the NIRS fetal probes during uterine contractions, has not been clearly defined. Using novel methods of collection and analysis of NIRS data, the technique of Intensity Modulated Optical Spectroscopy (IMOS) has the unique potential to provide ...