CONFIGURATION OF THE FETAL ELECTROCARDIOGRAM IN RELATION TO FETAL ACID‐BASE BALANCE AND PLASMA ELECTROLYTES

Abstract

SummaryThe configuration and time constants of the fetal electrocardiogram have been analyzed in relation to maternal and fetal acid‐base status and plasma electrolytes in 102 cases in which the fetus was considered to be “at risk”.Computer analysis of the results showed that fetal acidosis is associated with prolongation of electrical systole (QT) and with T‐wave inversion, and that these changes became better defined at the time of delivery. Similar changes were seen in relation to fetal hyperkalaemia. A comparison of scalp blood pH and corrected QT times has shown that scalp blood pH provides the more reliable method for prediction of fetal condition at birth.Maternal plasma sodium and potassium concentrations showed a highly significant positive linear correlation with fetal plasma sodium and potassium concentrations. Fetal plasma potassium levels showed a significant negative relationship with fetal blood pH and standard bicarbonate values. In the presence of fetal acidosis the ratio of fetal to maternal plasma potassium concentration increases, and hence a gradient for potassium loss from the fetus develops.