[Acid-base equilibrium and oxygenation of the human fetus. Study of 73 samples obtained by cordocentesis]

Acid-base state and oxygenation of fetal blood were evaluated in a group of 73 appropriate for gestational age fetuses between 17 and 41 weeks of gestation; fetal blood was obtained by cordocentesis. We measured, on umbilical venous blood, pH, pCO2, bicarbonates and total CO2, pO2 and percent oxygen saturation; we obtained following results: pH = 7.309 +/- 0.054; pCO2 = 5.99 +/- 0.85 kPa; HCO3 = 22.16 +/- 1.90 mmol/l; total CO2 = 22.53 +/- 1.97 mmol/l; pO2 = 6.02 +/- 1.68 kPa; SaO2 = 0.71 +/- 0.18. In comparison with adult normal values, our results report in fetuses a frequent state of mild and mixed acidosis (in about 80% of cases), rather gazeous; pH is significantly correlated with pCO2 (r = -0.799), moreover there is also a metabolic origin in acidosis. We observed progressive modifications of acid-base state and oxygenation in fetal blood with advancing gestational age: decrease of pH and pO2, increase of pCO2 and bicarbonates; these changes appear mainly from 35th week of gestation, except for bicarbonates, which increase regularly during gestational period we have studied. Fetal acid-base state may be explained by physiological differences due to fetal life conditions, in comparison with adult life conditions. Results obtained in this population of normal fetuses can be considered as reference values for studied parameters.