There is no clearly established umbilical artery pH cutoff to be used for defining pathologic fetal acidemia (ie, the threshold associated with major neonatal morbidity or mortality). Classically, a pH cutoff of less than 7.20 has been used. Our goal was to define this pH cutoff more precisely. There were 3506 term newborns (2500 g or greater) with an umbilical artery pH of less than 7.20; these newborns were divided into five pH groups. Eighty-seven (2.5%) had a pH of less than 7.00, 95 (2.7%) a pH of 7.00-7.04, 290 (8.3%) 7.05-7.09, 798 (22.8%) 7.10-7.14, and 2236 (63.8%) 7.15-7.19. Two-thirds (66.7%) of the newborns with an umbilical artery pH less than 7.00 had a metabolic component in their acidemia, compared with 13.7% or less in all other pH groups. Significantly more (P<.05) newborns in the less than- 7.00 pH group had low (less than 3) 1- and 5-minute Apgar scores compared with the other four pH groups. In addition, neonatal death was significantly more common (P=.03) in newborns with a pH less than 7.00, and seven (50%) of the 14 deaths occurred in this group. The statistically significant pH cutoff for all seizures was less than 7.05 (P=.004), and for unexplained seizures was less than 7.00 (P=.01). Eight (67%) of the 12 unexplained seizures occurred in this latter pH group. Thus, a more realistic pH cutoff for defining pathologic fetal acidemia would appear to be less than 7.00.
© 1991 The American College of Obstetricians and Gynecologists