Abstract: Background：The differences in oxygen saturation in the early postnatal period and umbilical artery blood gas values among different altitude gradients are still needed to be explored, especially for the establishment of normal values of pulse oximetry (SpO2)and umbilical artery blood gas at high altitudes. Objective：To compare the distribution of SpO2 within 2 hours after birth and umbilical artery blood gas analysis in well full-term neonates at different altitudes. Design：Cross-sectional study. Methods：Healthy full-term neonates who were delivered consecutively in 4 hospitals of the Chinese High Altitude Neonatal Medicine Alliance (CHANMA) from September 7, 2022 to October 10, 2022 were included. Designated medical staff collected the baseline data of the newborn, and tested the SpO2 value of the right hand of the newborn within 10, 11 to 30, and 31 to 120 minutes after birth under the same environments with the same standard. Immediately after birth, the umbilical cord was clamped and umbilical arterial blood gas (pH, lactic acid and BE) was detected. The data was recorded in the database of the CHANMA through the computer network. According to the altitude level, they are divided into 2,000 m above sea level group, 2,400 m above sea level group and 3,500 m above sea level group. The SpO2 value of 95% was taken as the hypoxic high-risk cut-off value for comparison. Main outcome measuresSpO2 within 2 hours after birth. Results：A total of 229 cases were included with 73 cases in the 2,000 m altitude group, 42 cases in the 2,400 m altitude group, and 114 cases in the 3,500 m altitude group. There was no significant difference in gender, gestational age, birth weight and mother's age among the three groups. Tibetan distribution was statistically significant. The SpO2 of the overall newborn population gradually increased over time. The median SpO2 at 2,000 m altitude group was 96%, 98% and 100% in three continuous periods after birth (10, 11 to 30 and 31 to 120 minutes), and the 25th quantile was equal to, 2% and 3% higher than the hypoxic high-risk cut-off value. The median SpO2 of the 2400m altitude group was 88%, 90% and 94% in the three continuous periods after birth, and the 75th quantile was 6%, 4%, and 1% lower than the hypoxic high-risk cut-off value respectively. The median SpO2 of the 3,500m altitude group in 3 consecutive periods was 84%, 89%, and 92%, respectively, and the 75th quantile was 5%, 5%, and 1% lower than the hypoxic high-risk cut-off value. There was no significant difference in the umbilical artery blood gas pH value among different altitude groups. The lactic acid was significantly higher and the BE was significantly lower in the 2,400 m altitude group and the 3,500 m altitude group than that in the 2,000 m altitude group, and the difference was significant in infants with cesarean birth as well. There was no statistically significant difference in SpO2 within 2 hours after birth and umbilical artery blood gas between newborns of Tibetan and other ethnic groups. The SpO2 of newborns of Tibetan and other ethnic groups showed an upward trend over time. The dispersion of point values was significantly narrowed, and 22.8% (26/114) of SpO2 value was higher than the hypoxic high-risk cut-off value. Conclusion：SpO2 in healthy full-term neonates within 2 hours of birth was significantly lower than the hypoxic cut-off values in altitudes above 2,000 meters, and higher at the altitude of 2,000 m and 3,500 m. There was not significant difference in SpO2 between Tibetans and other ethnic groups at 3,500 m altitude area.

Key words: High altitude, Neonate, Oxygen saturation, Umbilical artery blood gas