Objective:To determine oxygen saturation (SpO2) trends in healthy preterm newborns during the first 15 min after birth and to ascertain factors affecting SpO 2 changes during that period.Study Design:An observational study was conducted. Preterm newborns with gestational age (GA) less than 35 weeks, who did not require oxygen supplementation during the first 15 min of life, were enrolled. Pulse oximetry was applied to the right hand immediately after birth. SpO2 data were recorded continuously every 2 s and were then transferred to a Microsoft Excel spreadsheet for analysis. The time to reach a stable SpO2 85 ≥or ≥90% was described by the Kaplan-Meier method and compared using log-rank test.Result:A total of 102 preterm newborns were eligible, of whom 27 were excluded, resulting in 75 newborns enrolled into the study with a median (range) GA of 35 (29 to 35) weeks, median (range) birth weight of 2390 (1270 to 2990) g and median (range) Apgar scores at 1 and 5 min of 9 (5 to 10) and 10 (7 to 10), respectively. There was a gradual increase in SpO 2 with time. The median (interquartile range, IQR) SpO 2 at 2, 3, 4, 5 and 6 min was 77% (72 to 92), 84% (75 to 94), 88% (80 to 94), 90% (79 to 95) and 95% (85 to 97), respectively. Newborns with a lower GA seemed to have lower SpO 2 values. The median (IQR) time to reach a stable SpO2 ≥85 or ≥90% was 4 (3 to 6) and 5 (3 to 57) min, respectively. The mode of delivery was a significant factor affecting SpO 2; infants delivered by cesarean section had a significantly lower SpO2 and took a longer time to reach SpO2 ≥85% compared with those delivered by vaginal delivery (HR1.96, 95% CI1.11 to 3.49; P0.02). All enrolled newborns had no serious complications and they survived to discharge.Conclusion:SpO 2 in preterm newborns gradually increased with time. Approximately half of the preterm newborns had an SpO2 <90% during the first 5 min of life. Infants delivered by cesarean section had a lower SpO2 than those delivered by vaginal delivery. © 2010 Nature Publishing Group All rights reserved.