[Risk of neonatal acidosis and maternal respiration during labor].

Background: The reported incidence of neonatal acidosis varies++ significantly in different obstetrical departments. We wanted to investigate to which extend neonatal acidosis is depended on maternal respiration patterns during the third stage of labor.

Methods: Maternal arterial blood gas analysis was performed in 101 term pregnancies. Fetal acid-base parameters from arterial and venous umbilical blood were assessed simultaneously. SPEARMAN rank correlation (rs) was used to investigate the statistical relationship of maternal and fetal blood gas parameters and pH-values. Moreover a computer model was developed to describe the influence of maternal respiration on neonatal acidotic risk figures.

Results: A highly significant correlation was established between corresponding variables in maternal arterial blood and in venous umbilical blood (rs > or = 0.500, 2P < 0.001). These correlations were not as striking when comparing maternal parameters with corresponding variables in arterial umbilical blood. The partial oxygen pressure in arterial and venous umbilical blood did not show any correlation with the variables of the maternal acid-base status. In the computerized simulation model mild maternal hyperventilation during the third stage of labor decreased the risk of neonatal acidosis (pH, UA < 7.100%) by approximately 25% without evidence of lack of fetal oxygen supply.

Conclusions: A mild maternal hyperventilation synchronized with uterine contractions during the third stage of labor in combination with rapid breathing when delivering the fetal head has a favourable influence on the neonatal acid-base balance. In this study there is no indication that such an obstetrical management results merely in a laboratory artifact, because according to our data there was indeed no indication of compromised fetal oxygen supply. Routine fetal blood sampling also from venous umbilical blood appears to be useful in differentiating between combined feto-maternal and isolated fetal variations in actual pH-values.