In 1906, Cremer1 first recorded fetal deflections of about 0.5 mm. amplitude superimposed on the maternal electrocardiogram of nine-month gravid women by a string galvanometer electrocardiograph taking abdominovaginal and abdominorectal leads. Since then others2-10 have tried various methods with different instruments, such as special electrocardiograph with amplifiers, increased standardization even up to 20 cm. per millivolt, and the use of the electroencephalograph. Although fetal deflections are obtained in almost 90% of gravid patients, recording of fetal P, QSR, and T waves are still inadequate. More complex instrumentation based upon electronic cancellation of the maternal tracing will be helpful in this respect.11
As a basis for the subsequent study of the effect of maternal hypertension on the fetal heart rate, a simple method, similar to that employed by Pfister and Plice,12 was used for the determination of the fetal heart rate in normotensive pregnancy.
WONG M, CASSELS DE. The Fetal Electrocardiogram. AMA Am J Dis Child. 1960;99(1):4-7. doi:10.1001/archpedi.1960.02070030006002