In this study, the objective is to compare neonatal cerebral electrical activity within 3 days after birth across different altitude areas using amplitude-integrated electroencephalography (aEEG), and establish reference value for each altitude level.

Inclusion Criteria:

1. Singleton term infants (gestational age between 37 0/7 and 41 6/7 weeks) born in the participating hospital.
2. Infants appear well as defined by normal vital signs (heart rate ranging from 110 to 180 beats/min, respiratory rate ranging from 30 to 60 breaths/min, temperature ranging from 36.5°C to 37.5°C), absence of signs of illness such as cyanosis, respiratory distress and heart murmur.
3. The mother is permanent residence of the current altitude level and live in the study area for the entire duration of pregnancy.

Exclusion Criteria:

1. Need for supplemental oxygen or assisted ventilation.
2. Any evidence of intrauterine distress such as meconium-stained amniotic fluid, Apgar score <7 at 1 or 5 min.
3. Referred to neonatal intensive care unit or neonatology department for any reason other than observation.
4. With major congenital anomaly.
5. Probes cannot be properly placed due to scalp lesions or hematomas.
6. Reject or withdraw from the study.

Healthy neonates at different altitude levels