[Effect of labor on the acid-base equilibrium of the newborn infant]

The values of pH, PCO2, PO2 and base excess were measured at the time of birth, from the umbilical artery, in a group of 19 normal newborn infants from vaginal deliveries and compared to 19 infants born by elective cesarean sections without labor. The value of pH was significantly lower (7.23 +/- 0.06) in vaginal deliveries compared to elective cesarean sections (7.27 +/- 0.03) p less than 0.01. The best correlations occurred between pH and PCO2 (r: 0.72 p less than 0.01) in vaginal deliveries and pH and base excess (0.73 p less than 0.01) in cesarean sections. Normal values for umbilical arterial pH should consider the influence of labor in the acid base balance of the newborn infant. We consider that pH value under 7.11 (mean -2 SD) in vaginal deliveries and under 7.21 in elective cesarean sections are indicative of neonatal acidosis.