The reliability of pH-values in fetal blood samples - A study of the second stage

In 119 cases fetal blood analysis (FBA) was done in the last 15 minutes before birth together with blood sampling from the umbilical artery (UA) immediately after delivery before the first breath. Using the measured pH-values we investigated the relationship between these variables, in particular the degree of influence of considerable caput succedaneum on pH-values in peripheral blood. Our investigation was performed during the time just before delivery, when the disturbance of blood circulation in the presenting fetal part whuld have the highest influence on pH-values measured from peripheral blood samples. We kept in mind especially the critiques of FBA by WULF et al. [21] and ASSALI [2]. As other authors have concluded, we found a high degree of correlation between the pH evaluated by FBA and that determined in the umbilical artery blood. The coefficient of correlation was: pHact r=0.82 pHqu40 r=0.78. The relationship between the corresponding pHvalues in peripheral (FBA) and arterial (UA) blood is given in Fig. 1 a and Fig. 1 b. The correlation of quadrants showed for the actual pH as well for the pHqu40 p less than 0.01. As derived form this, a high degree of correlation between the pH-values can be seen. The mean pH-values were: (see article) 42 of the children had a severe or moderate caput succedaneum. Fig. 2a and 2b show the relationship between central and peripheral pH-values in these cases. Again a good correlation between the pH-values was observed as in the whole collective. The coefficient of correlation was: pHact r=0.78 pHqu40 r=0.79. Caput succedaneum seems to have only minimal influence on the pH of blood obtained from the presenting fetal part. These results lead us to conclude that blood sampling from the presenting fetal part in the second stage provides almost indentical pH-values as in the central fetal blood.