Abdominal fetal EKG noise removal.

UNLABELLED

Accurate detection of the fetal heart signal (FEKG) early during pregnancy enhances the physician's ability to diagnose possible congenital cardiac defects. However, FEKG acquisition is hampered by excessive noise contamination from the maternal ekg (MEKG) and uterine muscular contraction.

METHODS

A new computerized system was developed to record FEKG and MEKG signals from multiple leads. Removal of noise sources was performed using a blanking procedure, which selectively removes MEKG signal, and signal averaging procedure.

RESULTS

20 subjects showed 11 positive and 9 negative findings of FEKG. Blanking out the maternal QRS complex also removed part of the fetal signal making it unusable. The signal averaging procedure applied to 10-20 maternal QRS's still produced false positive fetal QRS signals. Two of the negative results were from biological noise with QRS type waveform and frequency of 8.75Hz. The depth of the fetus (5-10 cm) and period of gestation (17-40 weeks) had no bearing on finding FEKG.

CONCLUSION

Blanking is not an optimal method for maternal noise removal because of removal of some fetal QRS complex. Averaging is a viable method except in cases where the peak fetal signals are less than 75 micro Volts. Preliminary studies using an adaptive algorithm with the maternal chest EKG as reference promises to be a better solution for maternal EKG removal.