OBJECTIVE: To study the role of pH value of umbilical artery blood in the diagnosis and the assessment of prognosis of neonatal asphyxia. METHODS: A total of 140 single term newborn infants who were found abnormal by the fetal electrocardiogram monitoring were enrolled. The pH value of umbilical artery blood was measured immediately after birth. The Apgar score was performed 1 minute and 5 minutes after birth. The infants with the Apgar score ≤ 7 (n=62) were transferred to the pediatric ward for further management after resuscitation. Serum CTnI content was determined 24 hrs after birth. RESULTS: pH value of umbilical artery blood was positively correlated to 1 min and 5 min Apgar scores (r=0.513 and 0.478 respectively; P<0.01). There were significant differences for the umbilical pH value in infants with different Apgar scores (P<0.01). Serum CTnI content was negatively correlated to 1 min and 5 min Apgar scores (r=-0.614 and -0.569 respectively; P<0.01). The infants with umbilical artery pH value of more than 7.2, 7.0-7.2 and less than 7.0 had serum CTnI contents of 31.82±8.63, 53.24±11.18 and 79.36±18.51 ng/L, respectively (P<0.01). There was a negative correlation between umbilical artery pH value and serum CTnI content (r=-0.578, P<0.01). The incidence of organ injuries increased significantly with decreasing Apgar scores (P<0.05) and showed a negative correlation with 1 min and 5 min Apgar scores (r=-0.548 and -0.496 respectively; P<0.01). The infants with umbilical artery pH value of more than 7.2, 7.0-7.2 and less than 7.0 had the incidence of organ injuries of 36.4%, 60.0% and 83.3%, respectively (P<0.05). There was a negative correlation between umbilical artery pH value and the incidence of organ injuries (r=-0.578, P<0.05). CONCLUSIONS: Umbilical pH value correlates with Apgar score and may serve as sensitive indexes together with Apgar score for the diagnosis of neonatal asphyxia. Umbilical pH value is useful in the assessment of severity and prognosis of neonatal asphyxia.［Chin J Contemp Pediatr, 2009, 11 (7):521-524］