Noninvasive FECG for estimating the fetal heart rate

Decelerations of fetal heart rate have been known to be associated with fetal distress. Continuous fetal heart rate monitoring was expected to result in dramatic reduction of undiagnosed fetal hypoxia, but the outputs of FHR monitors were often unreliable and difficult to interpret, resulting in increased rates of caesarean deliveries of healthy infants. The most accurate method for measuring FHR is direct fetal electrocardiographic monitoring using a fetal scalp electrode. This is possible only in labor, however, and is not common in current clinical practice because of its associated risks. Noninvasive FECG monitoring makes use of electrodes placed on the mother´s abdomen. This method can be used throughout the second half of pregnancy and is of negligible risk. However, it is often difficult to detect the fetal QRS complexes in ECG signals obtained in this way, since the maternal ECG is usually of greater amplitude in them. Other features of the direct fetal ECG, such as FHR variability, may be useful independent indicators of fetal status. There are no accepted techniques for assessing such features from noninvasive FECG, however. This paper describes a method for locating QRS complex in noninvasive FECG, using techniques based on MECG cancellation, and Principal Component Analysis (PCA). The proposed method locates the fetal QRS complexes with efficiency above 80%.