Predictive value of fetal scalp pH and base excess for fetal acidosis and poor neonatal outcome

The objective of this study is to assess retrospectively the predictive value of fetal scalp pH and base excess (BE) for fetal acidosis and poor neonatal outcome in term, low-risk, spontaneous deliveries with suspicious or pathological intrapartum cardiotocography (CTG) tracings.

Umbilical artery pH and BE values obtained immediately after delivery and Apgar score were the outcomes under consideration. Statistics included receiver-operating characteristic curve (ROC) and multiple logistic regression analysis.

Four hundred and six deliveries were included in the study. Scalp pH < 7.20 predicted umbilical pH ≤7.1 with 64.3% sensitivity and 92.9% specificity (p < .001). The corresponding positive-predictive value (PPV) was 24.3% and the negative-predictive value (NPV) was 98.6%. Scalp BE ≤ -7 mmol/l (a cut-off value provided by ROC curve analysis) predicted Apgar score ≤ 7 at 5 min with 61.9% sensitivity and 91.7% specificity (p < .001). The corresponding PPV and NPV were 29.5 and 97.7%, respectively. Neither scalp pH nor BE was significantly associated with umbilical BE values. Infants with intrapartum BE ≤ -7 mmol/l were 30 times on an average more likely to get a low Apgar score, independently of intrapartum pH values.

Our study supports the consideration of both scalp pH and BE values, when fetal blood sampling (FBS) is used.