ABSTRACT
UNLABELLED: Clinical and animal experiments suggest that fetal metabolic acidosis is influenced by placental transfer of lactate and bicarbonate. It was the aim of this study to answer the following questions: What kind of relationship does exist between fetal metabolic acidosis and maternal metabolic acidosis? Does fetal metabolic acidosis coincide with alterations of fetal heart rate and fetal oxygenation? Does the maternofetal difference of base deficit reflect fetal oxygen deprivation more accurately than the measurement of fetal base deficit alone? What is the maternofetal difference of base deficit in normoxia and mild hypoxia? In 100 pregnant women (gestational age greater than 37 weeks, fetal weight greater than 3 rd percentile) a fetomaternal blood analysis (FMBA) was performed during labour and immediately after delivery. The metabolic acidosis was measured as base deficit of extracellular fluid (BDECF). RESULTS: The fetal metabolic acidosis depends mainly on the buffer base concentration in the maternal blood. Moderate repetitive hypoxemia with no severe pathological FHR-alterations do not show a significant relationship to fetal metabolic acidosis. Moderate hypoxia (defined as the combination of oxygen saturation below 30%, periodical decelerations and basal fetal heart rate above 160 b/min) can be recognized most accurately by determining the maternofetal differences of BDECF. In fetal normoxia BDECF in the maternal blood is 4 mmol/l higher than in the fetal blood, in moderate hypoxia the maternofetal difference of BDECF is reduced to 1 mmol/l. These findings are in accordance with the results of Roversi et al. (1975). Conclusions for the intensive surveillance of the fetus during labour by fetal blood analysis: Within the range of pH 7.10-7.30 the maternal BDECF should be determined in addition to the fetal BDECF to calculate the maternal fetal difference of BDECF. If BDECF in the fetus exceeds the maternal BDECF, the risk of fetal hypoxia is increasing. In these cases, delivery should be performed as soon as possible avoiding additional hypoxic or mechanical birth injuries. The technical procedure of fetal maternal blood analysis is described and the difficulties of routine use are discussed.
