Pathologic fetal acidemia

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 less than .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.