Prediction of Hypoxic Acidemia in Last 2 Hours of Labour in Low-Risk Women.

Abstract

Prediction of hypoxic acidemia in neonates using cardiotocogram (CTG) features continues to be challenging. The objective of this study was to explore the association between contraction frequency and fetal heart rate characteristics with hypoxic acidemia in low-risk women in labour. Cases were singleton, vertex, in labour with umbilical artery pH ≤7.05. Controls were the next consecutive birth with pH ≥7.15, matched for gestational age, maternal age, and parity. Obstetrical complications and maternal comorbidities were excluded. CTG features were tabulated for the last 2 hours of labour. "Cut-off points" above which acidemia is more likely were calculated for significant variables (Canadian Task Force Classification II-2). A total of 190 case-control pairs were included. Among cases we observed greater marked variability, tachycardia, variable and late decelerations, and fewer accelerations and early decelerations. A conditional logistic regression model included tachycardia, accelerations, total decelerations, and contractions. Tachycardia and total decelerations (variable, late) were significant. Tachycardia was most specific in predicting neonatal acidemia, whereas total (variable, late) decelerations were most sensitive. Late decelerations alone and total (variable, late) decelerations were similarly predictive for detecting neonatal acidemia using receiver-operating characteristic analysis; tachycardia was least discriminatory. Acidemic neonates were more likely to have CTGs with ≥11 late decelerations, ≥15 total decelerations (variable, late), and at least 80 minutes of tachycardia in the last 2 hours of labour. Tachycardia, late decelerations, and total (variable, late) decelerations were associated with acidosis in our population. Identifying "cut-off" points for the frequency of significant CTG features should be explored as a potential screening tool for neonatal acidemia.