Physiological development of a mixed metabolic and respiratory umbilical cord blood acidemia with advancing gestational age

Abstract

Objective To investigate respiratory and metabolic components of gestational age-dependent umbilical cord blood gas changes. Study design Cord blood gases were determined in 1336 vigorous singletons with uncomplicated cephalic vaginal delivery at 37–43 weeks. Linear regression analysis and non-parametric statistics were used with a P < 0.05 being significant. Results Gestational age correlated negatively with arterial pH and HCO 3 − and positively with pCO 2 and base deficit. Venous blood showed corresponding changes except for pCO 2, which was independent of gestational age. Arterial pCO 2, but not venous, correlated positively with birthweight deviation from the mean. The fractional fetal CO 2 production per birthweight unit and the fractional placental CO 2 clearance per placental weight unit were not correlated with gestational age. Conclusions A mixed respiratory and metabolic cord blood acidemia develops with advancing gestational age. The respiratory component depends on an increased ‘CO 2 load’ from the growing fetus and not on deterioration of placental gas exchange. The etiology of the metabolic component is yet unknown.