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Bioelectrical fetal heart activity being recorded from maternal abdominal surface contains more information than mechanical heart activity measurement based on the Doppler ultrasound signals. However, it requires extraction of fetal electrocardiogram from abdominal signals where the maternal electrocardiogram is dominant. The simplest technique for maternal component suppression is a blanking procedure, which relies upon the replacement of maternal QRS complexes by isoline values. Although, in case of coincidence of fetal and maternal QRS complexes, it causes a loss of information on fetal heart activity. Its influence on determination of fetal heart rate and the variability analysis depends on the sensitivity of the heart-beat detector used. The sensitivity is defined as an ability to detect the incomplete fetal QRS complex. The aim of this work was to evaluate the influence of the maternal electrocardiogram suppression method used on the reliability of FHR signal being calculated.

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At present, noninvasive recording of abdominal fetal electrocardiogram and analysis of the fetal heart rate variability seems to be the most promising method to detect the fetal hypoxia. The main problem is to obtain a good quality fetal ECG, which is strongly distorted by maternal component of dominating energy. The paper presents the new method of maternal electrocardiogram recognition and suppression relying on determination of template maternal PQRST complex and its subtraction during consecutive maternal cardiac cycles. The efficiency of the developed method was evaluated and related to three other selected methods for maternal ECG suppression using dedicated coefficients created for this comparison.