Aims: To compare the predictive ability for neonatal acidemia of individual components of intrapartum cardiotocography (CTG) described by National Institute of Child Health and Human Development (NICHD) system and deceleration area.
Design: Case-control study.
Setting: Spanish tertiary obstetrical hospital.
Population: CTG patterns of 102 acidemic fetus (umbilical arterial cord gas pH ≤7.10, base deficit (BD) > 8) and 102 nonacidemic controls (umbilical arterial cord gas pH > 7.10).
Methods: Two reviewers blind to clinical and outcome data analyzed the last thirty minutes before delivery of 204 fetal heart rate (FHR) tracings, extracting those features defined by NICHD and certain measures of FHR decelerations, including deceleration area, not considered by this system.
Outcome measures: The primary outcome was the predictive ability of NICHD features and non-NICHD deceleration measures for fetal acidemia. The secondary outcome was the impact of deceleration area in the last 30 min of labor on gasometry components (pH, BD and lactate).
Results: Minimal variability (area under the curve (AUC) 0.74), total number of late (AUC: 0.75) and prolonged decelerations (0.77) were the three NICHD features with the greatest predictive ability for fetal acidemia in the last thirty minutes of labor. Total deceleration area demonstrated the highest discrimination power (AUC: 0.83) of all the analyzed elements. For each cm2 the area increases in the last 30 min of labor, pH decreases 0.08 units, BD increases 0.272 mEq/L and lactate 0.183 mEq/L.
Conclusions: Total deceleration area showed the greatest predictive ability for fetal acidemia and its measure could help to estimate intrapartum fetal acid-base status.
Keywords: Cardiotocography; deceleration area; fetal buffer system; fetal heart rate decelerations; neonatal acidemia.