Monitoring placental oxygenation and metabolism using a time-domain near infrared spectroscopy system

Placental dysfunction contributes substantially to adverse perinatal outcomes, yet current antenatal monitoring tools provide limited direct assessment of placental physiology. We used an optimised time-domain near-infrared spectroscopy (TD-NIRS) system (MAESTROS II) to measure placental oxygenation (PltO 2 ) and metabolism across gestation and describe expected physiological behaviour and provide preliminary reference data in healthy pregnancies. In this prospective observational study, 113 women with low-risk singleton pregnancies underwent 30-minute TD-NIRS monitoring sessions. Placental position and depth were assessed by ultrasound, and skin pigmentation by Fitzpatrick scale. PltO 2 , changes in cytochrome-c-oxidase oxidation state (oxCCO), and the phase relationship between a haemodynamic oxygen-related signal (haemoglobin difference, HbD) and oxCCO were analysed. Mean PltO 2 was 50.4% (±6.6%) with no significant gestational change. Placental depth, location, and skin tone did not significantly affect measurements. Wavelet analysis demonstrated predominantly out-of-phase HbD-oxCCO relationships, suggesting independent metabolic regulation. These findings provide reference data and support the potential clinical utility of monitoring placental function using optical measurements of oxygenation and metabolism.