ABSTRACT
We studied the relationships between fetal hemoglobin concentration, acid base status,
and lactate concentration in umbilical venous and fetal heart blood in 157 fetuses
affected by blood group incompatibility who had been exposed for 214 fetal blood sampling
procedures (cordocentesis in 153 and intracardiac puncture in 61 cases). All blood
samplings were obtained before fetal blood transfusions were administrated. The results
indicate that the human fetus can maintain a normal acid-base status until a 50% reduction
of the hemoglobin concentration. A further reduction of hemoglobin is associated with
an accumulation of lactate both in umbilical venous and fetal heart blood. The partial
oxygen tension and the oxygen saturation in umbilical venous blood remained virtually
unchanged with decreasing hemoglobin concentration (r = -0.11, P = 0.21; r = 0.09, P = 0.31, respectively), whereas these parameters decreased significantly (r = 0.33, P = 0.02; r = 34, P = 0.02) in blood obtained from the fetal heart. The partial carbon dioxide tension
of umbilical vein blood decreases significantly with a reduced hemoglobin concentration
(r = 0.25 P = 0.008). We speculate that these alterations in acid-base status in umbilical vein
and fetal heart blood reflect a circulatory transition from a high to a low cardiac
output as the hemoglobin concentration decreases.
