Umbilical cord pH and base excess values in relation to adverse outcome events for infants delivering at term

Abstract

Objective This study was undertaken to determine the relationship of umbilical cord pH and base excess (BE) values to adverse neonatal outcomes for a large tertiary hospital population delivering at term. Study design The perinatal/neonatal database of St. Joseph's Health Care, London, Canada, was used to obtain the umbilical cord pH and BE values, incidence of adverse neonatal outcomes, and patient demographics for all term (≥37 weeks' gestation), singleton, liveborn infants with no major anomalies delivering between November 1995 and March 2002 (n = 20,456). Statistical analyses included χ 2 analysis, logistic regression models to develop odds ratios and creation of receiver operating characteristic (ROC) curves with area under curve (AUC) calculations. Results Umbilical vein and artery pH and BE values for this tertiary care population averaged 7.33 ± 0.06 and 7.24 ± 0.07, and −4.5 ± 2.4 and −5.6 ± 3.0 mmol/L, respectively. Apgar less than 7 at 5 minutes, neonatal intensive care unit (NICU) admission, and assisted neonatal ventilation had significant inverse relationships with both umbilical artery and umbilical vein pH and BE (all P < .0001), with marginal increases in the incidences of these outcomes beginning with cord blood values close to the mean, and more substantial increases with cord values less than 1 or 2 SD below the mean, depending on the outcome studied. The ROC AUC for all these relationships were significant (P < .001) ranging from 0.76 to 0.79 when predicting Apgar less than 7 at 5 minutes to 0.68 to 0.70 when predicting NICU admission, and with cutoff cord blood values at which sensitivity and specificity were maximized again close to mean values. For each of these neonatal outcomes, the relation to cord blood values was similar with little difference in the data analysis whether using pH or BE values, and whether from the umbilical artery or vein. Conclusion There is a progression of risk in term infants for Apgar less than 7 at 5 minutes, NICU admission, and need for assisted ventilation with worsening acidosis at birth, which begins with cord blood values close to mean values indicating a higher threshold for associated acidemia with these outcomes than is seen for more severe neonatal outcomes.