NOVEL APPROACH FOR INTERPRETATION OF FETAL HEART RATE IN THE SECOND STAGE OF LABOUR

OBJECTIVE: Intrapartum fetal heart rate monitoring has become the standard technique to assess fetal well being during labor. However, most of the guidelines for the interpretation of cardiotocography (CTG) tracings do not distinguish between the first and the second stage of labor. The only classification available for the interpretation of the CTG in the second stage of labor is that of Piquard (modified after Melchior & Bernard). However, this classification is not widely accepted and has been developed more than 25 year ago. The main aim of our study was to revaluate the classification of Piquard of the CTG in the II stage of labor and verify whether it is still applicable. Secondary aims were to verify whether there was a correlation between the CTG recorded in the second stage with that recorded in the first stage and assess whether there are patterns associated to neonatal acidemia at birth. STUDY DESIGN: This is a 2-year retrospective cohort study of 2297 singleton, pregnancies who delivered vaginally in our Institution: we included low risk as well as complicated pregnancies. Inclusion criteria were the presence of at least the final 60 minutes of continuous and technically interpretable tracings in the first stage and a technically interpretable tracings recorded continuously in the second stage lasting at least 10 minutes, and the presence of umbilical arterial oxygenation and acid base balance measured at the time of delivery. CTGs were extracted prospectively and analyzed retrospectively blind to the clinical information by a single reviewer trained in CTG interpretation. Neonatal acidemia was defined by the presence of umbilical arterial cord pH of 7.10 or less. Multiple logistic regression model was used for statistical analysis. RESULTS: Slightly less than 50% of the tracings (49.2% in nulliparous and 46.7% in multiparous) recorded in the II stage could be classified according to the original six types proposed by Piquard et al. In addition, types 2B, 3 and 4 were very rare accounting only for 0.5% of tracings both in nulliparous and multiparous. The remaining tracings were represented by a combination of these 6 types. Acidemia at delivery was highly associated with the presence of repetitive variable decelerations (aOR 4.4; 95% CI: 1.95-9.95) and minimal FHR variability (aOR, 5.95; 95% CI:1.94-18.26) in the I stage. In the II stage, acidemia was associated with type 1-4 (aOR 9.05, 95% CI: 1.59-51.5) and 1 (aOR 4.4, 95%; CI 1-19.5). We found that the length of II stage > 120 minutes (aOR: 4.3, 95%; CI 1.29-14.39, induction (aOR, 1.76; CI 1.04-3.61of labor was a risk factor for acidemia), BMI (for women with BMI 25 aOR : 8.3, 95%; CI 2.06-33.2) were all independently associated with acidemia at birth. Pathology (aOR 0.181, CI 0.024-1.381), parity (a OR,0.86, CI 0.424-1.755), male sex ( a OR 1.26, CI 0.69-2.3) and neonatal weight at birth at various centiles were not associated with acidemia. Gestational age was protective against acidemia (aOR 0.048, CI 0.006-0.376). Of type 1 Piquard specific criteria that we defined as malignant were very significantly associated with acidemia CONCLUSIONS: The results of the study suggest that there is need for a novel classification of the CTG in the II stage: fetuses with a \u201cbenign\u201d CTG pattern (type 1) had a fourfold risk of acidemia in labor. The combination of type 1 and 4 (type 1 + bradycardia at the extreme end of labor) carried a ninefold risk of acidemia at delivery. In addition, attention has to be paid to \u201cmalignant\u201d criteria of Piquard type 1 for the highest association with acidemia. Key words : II stage of labor , CTG patterns in labor, acidemia at birth