This study will enroll normal full-term infants and very low birth weight preterm infants who have no major neonatal disease. Cranial Doppler ultrasound examination will be performed on all infants at term age. Hemodynamic parameters will include peak systolic velocity, end diastolic velocity, resistance index and pulsatility index for the bilateral anterior cerebral arteries and middle cerebral arteries. Neurobehavioral development will be administered on the same day using the Neonatal Neurobehavioral Examination- Chinese version.