Second-stage fetal heart rate abnormalities and type of neonatal acidemia.

The type of acidemia (umbilical arterial pH less than 7.2) occurring in newborns with second-stage baseline fetal heart rate (FHR) abnormalities was evaluated in 277 term gestations. Umbilical arterial acidemia occurred in 40% of the neonates with moderate to severe bradycardia (25 of 63), in 30% with mild bradycardia (16 of 53), and in 22% with tachycardia (seven of 32), compared with only 6% (eight of 129) of those with a normal FHR (P less than .05 in each of the three comparisons). The majority (31 of 56, 55%) of the acidemic neonates had a mixed respiratory-metabolic pattern, whereas 13 of 56 (23%) had a respiratory pattern and 12 of 56 (21%) had a metabolic pattern. The mean umbilical arterial buffer deficit (mEq/L) was significantly greater (P less than .0005) in newborns with metabolic acidemia (-15.9 +/- 2.8) than in those with either mixed (-9.6 +/- 2.5) or respiratory (-6.4 +/- 1.9) acidemia. We conclude that baseline second-stage FHR abnormalities can predict which newborns are at increased risk of having umbilical arterial pH below 7.2 at birth. Selective determination of umbilical arterial pH and blood gas analysis may be useful in assessing intrapartum management retrospectively.