https://iopscience.iop.org/article/10.1088/0967-3334/28/4/004/pdf (Publisher version)
Martens, S., Rabotti, C., Mischi, M., & Sluijter, R. (2007). A robust fetal ECG detection method for abdominal recordings. Physiological Measurement, 28(4), 373-388. doi:10.1088/0967-3334/28/4/004.