Umbilical artery blood acid-base analysis and fetal heart rate baseline in the second stage of labor.

OBJECTIVE: To evaluate the correlation between umbilical arterial acidemia and second-stage baseline fetal heart rate (FHR) abnormalities in Japanese newborn infants. METHODS: Subjects were 365 newborns, born at term. Specimens were obtained from the umbilical artery as soon as possible after delivery and blood gas determinations were performed within 5 minutes of delivery. FHR monitoring was performed in the second stage. RESULTS: Umbilical arterial acidemia occurred in 54.1% of the newborns with moderate to severe bradycardia, in 27.3% with mild bradycardia, and in 19.3% with tachycardia, compared with only 1.3% of those with a normal FHR (p < 0.001). The mean umbilical arterial base excess was significantly greater in newborns with metabolic acidemia (-13.9+/-2.9 mmol/l) than in those with either mixed (-11.5+/-2.8 mmol/l) (p < 0.02) or respiratory (-9.1+/-3.2 mmol/l) (p < 0.01) acidemia. CONCLUSION: The second-stage baseline FHR abnormalities were highly correlated with an increased risk of umbilical arterial acidemia at delivery.