Second stage fetal heart rate abnormalities and neonatal acidosis.

Of 403 newborns with either fetal heart rate (FHR) bradycardia or tachycardia during the last ten minutes of the second stage of labor, 20% had an umbilical cord pH of less than 7.20 at birth compared with only 4% of newborns who had a normal FHR during the last ten minutes of labor (P less than .0001). Thirty (18%) of 165 neonates with mild bradycardia and 33 (27%) of 121 neonates with moderate to marked bradycardia had cord pH values of less than 7.20 at birth (P less than .0001). Of the 117 neonates with tachycardia during the last ten minutes of the second stage, 17 (15%) had a pH of less than 7.20 (P less than .0001). There was a significant increase in low cord pH values when FHR variability was absent when compared with normal variability (P less than .0001).