Remote umbilical arterial blood pH analysis: accuracy, utility, and limitations

It is not always possible or feasible to perform routine umbilical artery blood sampling at birth. This study was undertaken to assess the accuracy of selective remote umbilical arterial blood analysis to retrospectively predict the original birth pH of any newborn. Umbilical arterial blood samples were obtained in two preheparinized syringes immediately following 1007 deliveries. One sample was analyzed within 60 minutes of delivery. The other was placed on ice and later analyzed at variable time intervals up to 180 hours postpartum. The results of each remote analysis were adjusted using a previously published regression equation to accurately identify which newborns had pH values < 7.00, < or = 7.10, or < 7.20 at birth. Among the 1007 newborns, there were 14 (1.3%), 44 (4.3%), and 187 (18.5%) who had pH values < 7.00, < or = 7.10, and < 7.20, respectively, at birth. Remote umbilical arterial samples analyzed within 72 hours of delivery correctly identified newborns with an original pH < 7.00, < or = 7.10, or < 7.20 with: (1) a sensitivity of 100, 82, and 84%, respectively; (2) positive predictive values of 100, 93, and 66%, respectively; and (3) a test efficiency of 100, 99, and 89%, respectively. Up to 72 hours after delivery, remote umbilical arterial blood pH analysis can be reliably used to accurately identify the newborn that was acidotic at birth.