## 4 Discussion  
This is the first report to use TRS to measure the absolute value of CBV and optical properties in term neonates immediately after birth. We obtained the following main results: (1) CBV shows a tendency to decrease after birth, but we found large variability in the absolute value of CBV across neonates; and (2) DPF and \(\upmu_{\text{s}}\)' were stable immediately after birth. These findings indicate that TRS can be a useful, simple, and noninvasive tool for the stable measurement of the absolute values of CBV and ScO\({}_{2}\) when we need to assess the immediate postnatal cerebral oxygen metabolism and hemodynamics in neonates. [PERSON] et al. [14] monitored the changes in CBV during the immediate postnatal transition period after elective cesarean delivery using NIRS. The mean decrease in total Hb from 2 to 15 min after birth represented a CBV decrease of 1.0 mL/100 g brain. They hypothesized that the CBV decrease after birth was mainly caused by postnatal increases in cerebral PaO\({}_{2}\) levels. This likely reflects a physiological process involving changes in the autoregulatory capacity of cerebral vessels in reaction to increasing pO\({}_{2}\) and decreasing pCO\({}_{2}\) levels after elective cesarean delivery. Our results following natural vaginal delivery in this study are consistent with those of previous reports. We speculate that this CBV decrease can be explained in two possible ways. Firstly, in the transition period, neonates are exposed to the stress of natural labor, which would cause greater hypoxia and hypercapnia. Secondly, as this would cause cerebral vasodilation, their reactions would improve within 1-2 min after birth and CBV would decrease by 15 min after birth. However, our findings indicate that neonates do not always show a clear decrease in CBV and that it has considerable variability. Thus, we consider that evaluation of the absolute value of CBV would more accurately reflect each characteristic cerebral hemodynamic pattern compared with the relative change in CBV alone. Both ScO\({}_{2}\) and SpO\({}_{2}\) gradually increased until 15 min after birth, as in previous reports (Figures 3 and 4). Although there have been many reports on whether this cerebral oxyHb/totalHb ratio would become a useful parameter for monitoring oxygen during the transition period, its value remains unknown. In this study, the ScO\({}_{2}\) pattern of V3 and V4 neonates was observed to increase similarly, whereas the CBV of V3 neonates was clearly decreased and that of V4 neonates showed little decrease. These results indicated that CBV may shows a different pattern, despite the similar pattern of ScO\({}_{2}\). Therefore, it is critical to monitor both CBV  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Neonate** & **Time after** & \multicolumn{3}{c}{**DPF**} & \multicolumn{3}{c}{**\(\upmu\)a (/cm)**} & \multicolumn{3}{c}{**\(\upmu\)s’ (/cm)**} \\ \cline{3-10}
**No. ** & **Birth (min)** & **762 nm** & **800 nm** & **836 nm** & **762 nm** & **800 nm** & **836 nm** & **762 nm** & **800 nm** & **836 nm** \\ \hline \multirow  
and \(\text{ScO}_{2}\) to detect dramatic changes in cerebral hemodynamics and oxygen metabolism in the neonatal transition period. For neonates with hypoxic ischemic encephalopathy, our group reported that combined CBV plus \(\text{ScO}_{2}\) at 24 h after birth using TRS had the best predictive ability for neurological outcomes [15]. In addition, we reported the \(\text{ScO}_{2}\) and CBV before and after transfusion in very low birth weight infants with anemia of prematurity and suggested that CBV and \(\text{ScO}_{2}\) may be useful markers for determining the need for transfusion [16]. Hence, monitoring of both CBV and \(\text{ScO}_{2}\) using TRS may help to determine oxygen use in the neonatal transition period.