Correlation between Intrapartum Cardiotocogram Findings and Cord Blood pH in Term and Preterm Labors

Abstract

Background: The purpose of intrapartum fetal monitoring by cardiotocograph (CTG) is to identify early signs of developing hypoxia so that appropriate action can be taken to improve the perinatal outcome. Although CTG findings are well known to monitor the progress of the labor due to the paucity of recommendations, there has always been a clinical dilemma as the term fetuses respond differently than a preterm fetus. However, umbilical cord blood pH can distinguish the infant at high risk for asphyxia and related sequel. Therefore, because of differences in fetal physiology in term and preterm fetuses, CTG findings vary, and hence the validity of CTG to determine fetal acidosis should be different. Aims and Objectives: This study aimed to correlate abnormal intrapartum CTG findings with umbilical cord blood pH in term and preterm labor and thus evaluate the success of CTG in predicting fetal acidosis during labor. Methods: The present study included 210 women in labor (70 preterm and 140 term) with abnormal intrapartum CTG that was classified as per 2015 revised International Federation of Gynecologists and Obstetrician (FIGO) guidelines. Immediately after delivery, 2 ml Umbilical artery cord blood sample was taken in a pre-heparinized syringe for analysis, pH <=7.2 was taken as acidosis and pH >7.2 was taken as normal. The measured data were general maternal characteristics which included gravida status, associated comorbidities, method of induction and character of liquor, the intrapartum CTG tracings recorded, the cord arterial blood pH and the neonatal characteristics such as APGAR score and neonatal outcome. Results: Data from 70 preterm labor was compared with 140 term labor. In this study, 20.9% of the babies had acidosis. Suspicious CTG due to decreased variability were more common in the preterm group than in the term group (21.4% vs. 8.6% p<0.05). Positive predictive value (PPV) of abnormal CTG for fetal acidosis in the preterm group was found to be higher than that in the term group, PPV of pathological CTG being even higher than suspicious CTG. Women with suspicious CTG had 82% less risk of fetal acidosis as compared to pathological CTG. Women with Bradycardia had 5.9 times the risk of fetal acidosis as compared with normal and tachycardia. Conclusion: Abnormal CTG should be managed appropriately without any delay to prevent acidosis and cord blood pH should be done in all labors with abnormal CTG. However, our findings of a higher incidence of lower cord blood pH and suspicious CTG due to decreased variability alone highlight the limitation of criteria currently used for interpretation of CTG in preterm labors.