Quantitative CTG appraisal sub partu with a new CTG score: diagnostic significance of the parameters of the acid-base balance in umbilical blood?

Abstract

As a role, the severity of "CTG pathology" in acute or chronic fetal hypoxia could only be registered but not quantified exactly by visual examination. For this reason, the term "CTG pathology" has not been unequivocally defined. The objective of the present study was to describe the dependence of fetal heart rate phenomena on the parameters of the acid-base balance quantitatively and to subject the latter to statistical analysis. The last 120 minutes of a total of 411 interference-free cardiotocograms directly registered intra partum (HP, 2 cm/min) were evaluated in terms of the visual appearance of CTG: the frequency level and the fluctuation of every single minute and the deceleration-area sum were considered for 30 CTG minutes per fetus. A new CTG score was conceived which envisages six points for the mean frequency according to specific definitions, three points for the deceleration-area and further six points for the fluctuation (long-term variability). The heart rate data and clinical factors were analyzed off-line using parametric and non-parametric test procedures with special programs (FORTRAN) on an IBM system (6150). Besides the pH values in the umbilical arterial and venous blood, direct measurements of blood gases (pO(2), pCO(2)) were also available in 113 cases, so that the base excess (mmol/l) and the oxygen saturation (%) could be calculated according to known algorithms. For the last 30 minutes ante partum, the CTG score correlates highly significantly (P << 10(-4)) with the actual pH value in the umbilical arterial blood (r = -0.6002). The correlation with the base excess is better (r = 0.642, P << 10(-4)), whereas the correlation with the directly measured pCO (2) is weaker (r = 0.587). Such strict correlations could not be demonstrated for oxygen saturation in the umbilical arterial or umbilical venous blood (r = -0.258, P = 0.0057 and r = -0.308, P = 0.0009). The good correlations of the variables of the fetal acid-base balance with the CTG phenomena registered with the score can be used for clinical purposes. However, analysis of the CTG with the naked eye is not practically feasible for the obstetricians; it must therefore be done per computer. Quantitative CTG analysis has created the perspective of a promising new method for fetal monitoring sub partu.