The correlation of maternal and fetal heart rates - an important aspect of CfG interpretation

Although cardiotocography (CTG) is the most commonly used method in perinatal monitoring. there are still some difficulties surrounding its interpretation. In many cases an unequivocal diagnosis is not possible without additional physiological information. The reasons may be either physiological or due to shortcomings of existing instrumentation. A typical example is shown in Figure 1, where the CTG reveals no reason for the acceleration of the fetal heart rate (FHR), Uterine activity is completely absent, and no fetal movement is detectable. Considering, however, the maternal heart rate (MHR). the acceleration becomes intelligible as a result of feto-maternal coupling. A most serious situation is documented in Figure 2. There is a quite normal CTG. no uterine activity and an FHR curve of rather good quality that reveals no abnormalities. But the simultaneously recorded fetal ECG shows severe arrhythmia. Probably no existing fetal monitor would have been able to detect this condition. We were able to recognize the arrhythmia because we monitored not only the fetal but also the maternal heart rate, which was found to be markedly abnormal. Our interpretation of the feta-maternal coupling indicated that a direct influence on the fetal cardiac system was to be expected, so we recorded the fetal ECG in order to check the inconspicuous FHR curve.