RESUMEN
BACKGROUND: Accelerations role during the second stage of labor has not been studied and current classification system NICHD downplays its presence. The objective of this study is to determine validity for acidemia detection of the loss of accelerations during the second stage of labor. MATERIAL AND METHOD: This is a one year retrospective case-control study of 102 neonates with acidemia defined as an umbilical cord gas pH≤7.10 compared to 100 non acidemic controls. The last thirty minutes of CTG were evaluated by two obstetricians blind to clinical and outcome data that classified tracings into categories according to NICHD definitions, determining the presence or absence of accelerations. Validity of NICHD categories and absence of accelerations were calculated. RESULTS: 85% of fetuses presented a category II tracing in the last 30 minutes of labor. Absence of accelerations was associated with neonatal acidemia (ORa 4.43). Category II tracings were not associated with acidemia after adjusting for confounding factors.Validity of the absence of accelerations during the second stage of labor was higher in terms of sensitivity (80.3%), specificity (54%) and global value (67%) to that of the presence of a category II tracing (96%, 24% and 60% respectively) in this period. CONCLUSIONS: The absence of accelerations during the second stage of labor shows a bigger validity for neonatal acidemia than the presence of a category II tracing.
