Acidosis in the vigorous newborn.

Simultaneous measurements of maternal arterial and umbilical cord blood pH, PCO2, and base deficit at delivery were studied in 168 live-born infants and their mothers. The correlations between maternal and umbilical parameters were highly significant (P less than .001) and were greater in vigorous than in depressed newborns. Mothers of vigorous acidotic infants had a lower pH and a higher base deficit than those of vigorous nonacidotic infants (P less than .001). However, the maternal-fetal differences were wider in the vigorous acidotic than in the vigorous nonacidotic newborns for all three parameters, and in both umbilical vein and umbilical artery (P less than .001). The data indicate that maternal acidosis accounts only partially for the acidosis observed at the time of delivery in the apparently normal fetus. With neonatal depression, the degree of acidosis is not dependent on maternal pH but on other factors. These factors may be influenced by maternal acidosis, but they are the major reasons for the neonatal depression, not the maternal acidosis.