The now widely used reference interval for pulse oxygen saturation of the neonate after 24 hours of birth has been developed relying on data from low altitude.It is not suitable for neonates at high altitude. At present, no reference interval has been established at high altitude, and the existing studies have many limitations. So this study was designed.

Knowledge of the reference interval of pulse oxygen saturation (SpO2) in neonates is crucial for accurate identification of neonatal hypoxemia. The now widely used standard was derived from low altitude data, which is not suitable neonates at high altitude. At present, many scholars have paid attention to this problem. But, previous studies still have some limitations. For example, they often only focus on a specific altitude. However, with the increase of altitude, the pulse oxygen saturation decreases in a curve, so their study results are only suitable for this specific altitude and can not be widely used.

Inclusion Criteria:

• Healthy singleton term infants with no clinical signs and symptoms (e.g., cyanosis, respiratory distress, heart murmur, etc.).

Exclusion Criteria:

• 1. Low birth weight (< 2500 g). 2. Need for oxygen. 3.1 or 5 minute Apgar score < 7. 4. Referred to the neonatal intensive care unit or neonatology department for various reasons. 5. Neonates discharged within 24 hours of birth. 6. Neonates diagnosed with congenital diseases in utero. 7. Refusal of consent.

All consecutively delivered and eligible neonates at the various medical centers at different altitudes during the study will be included. The study period is from November 20, 2021 to November 20, 2022.