Temporal Changes in Brain Light Scattering and Its Independent Variables Within 2 Days of Life

The reduced scattering coefficient (μ_s'), measured using time-resolved near-infrared spectroscopy (TR-NIRS) has been linked to brain water diffusion assessed by diffusion tensor imaging, suggesting its potential as a bedside marker of cerebral microstructure. However, the physiological determinants of μ_s' and its early postnatal changes remain unclear. This study examined clinical associations with cerebral μ_s' in healthy term newborn infants during the first 2 postnatal days. Eighteen newborn infants underwent TR-NIRS at 6 and 36 h postnatally. Associations between μ_s' and 14 clinical variables were analysed using generalised estimating equations. Median μ_s' was 7.395 cm^-1 (IQR: 6.140-8.159) at 6 h and 7.112 cm^-1 (IQR: 6.473-7.410) at 36 h, with no significant difference (p = 0.327). Male sex was associated with higher μ_s' (regression coefficient = 0.895, p = 0.007), whereas caesarean delivery (regression coefficient = -0.969, p = 0.012) was associated with lower μ_s'. A significant interaction between caesarean delivery and postnatal age indicated that the negative effect diminished between 6 and 36 h after birth (difference = 0.057, p = 0.016). These findings suggest delivery mode transiently influences brain scattering, whereas the effect of sex remains stable, supporting further investigation of TR-NIRS as an acute-phase cerebral marker.