Pulse oximetry offers real time and non-invasive estimation of arterial oxygen saturation in a cost-effective way, and has become a critical tool in guiding the usage of supplemental oxygen in sick newborns. During postnatal transition, pulmonary pressure decreases upon the activation of the lungs, and the ductus arteriosus constricts and closes upon the increase of partial oxygen pressure, which is negatively correlated with altitude. As a result, postnatal transition may be different at high altitudes. Umbilical cord blood gas analysis is now recommended in all high-risk deliveries because of its' value in providing information about preceding fetal hypoxic stress. But there are only limited studies about the SpO2 measurements during the first few hours after birth and umbilical blood gas analysis at high altitudes, especially at altitudes above 2500m. The primary outcome of the study is to determine the reference intervals for preductal oxygen saturation during first 2 hours of life stratified by different gestational age. The secondary outcomes is to establish the pH and lactate cutoff value of umbilical arterial blood gas at different altitude level.

Inclusion Criteria:

• Infants with a gestational age between 35 to 42 weeks who were born alive and appearing well as defined by:

  1. normal vital signs (heart rate ranging from 110 to 180 beats/minute, respiratory rate ranging from 30 to 60 breaths/minute, temperature ranging from 36.5°C to 37.5°C),
  2. absence of signs of illness such as respiratory distress.
  3. the mothers resided in the study area.

Exclusion Criteria:

• outborn, require resuscitative interventions at birth beyond blow-by oxygen,
• require admission for any reason other than observation or had a major congenital anomaly.

The study included infants with a gestational age between 35 to 42 weeks who were born alive and appearing well