We estimate the sample size of this study based on the cerebral blood flow velocity data of Kempley's study that showed 7.2 ± 3.5 and 10.7 ± 2.4 cm/s for the MCAs in 13 preterm and 8 full-term infants, respectively. As the power is set at 0.8 and the α level is at 0.05, at least 17 subjects were required for each group. This study will include 20 full-term and 20 VLBW preterm infants who are born at the National Taiwan University Hospital (NTUH) and the Mackay Memorial Hospital (MMH), Taipei, Taiwan. Written informed consent will be obtained from the parents before participation in this study.