A blind adaptive filter of an apparatus in an example employs a frequency domain ECG-feature vector and a time domain ECG feature vector with a maternal ECG parameter estimate and a set of candidate fetal ECG estimates that satisfy the frequency domain ECG-feature-vector, to extract a fetal ECG signal estimate from raw abdominal ECG signals of a pregnant female. The fetal ECG signal estimate satisfies the frequency domain ECG feature-vector and the time domain ECG feature vector.