Measurement of the Fetal Heart Rate During Pregnancy by a New Electrocardiographic Technique

Abstract

Summary An external technique for recording the fetal heart rate (FHR) during pregnancy is described. The system is based upon the detection of the fetal electrocardiogram (ECG) from the maternal abdomen and elimination of the maternal QRS complexes by a new system of subtraction. Fetal QRS complexes with an amplitude of 10 microvolts or more were processed to produce heart rate recordings of much higher quality than previously obtained with the phonocardiographic and ultrasonic systems. The proportion of successful recordings was reduced between 27 and 34 weeks of gestation due to the decrease in size of the fetal QRS complex which occurred at this time; this was a major drawback of the ECG system.

Fetal heart rate patterns at 20 to 24 weeks gestation as recorded by fetal electrocardiography

“…The technique is superior to Doppler ultrasound in evaluating fetal cardiac rhythms during epochs of fetal movement and it affords the temporal resolution required for true beat-to-beat variation (2, 7, 8). The equipment for recording fetal ECG is now commercially available.…”

Technical Aspects of Fetal and Intrauterine Pressure Monitoring

“…From approximately 20 weeks gestation the antepartum FHR can often be derived from the fetal ECG detected at the surface of the maternal abdomen, although this is often rather difficult between 28 and 34 weeks owing to the low amplitude of the signals at this time (Klöck et al, 1976;Wheeler et al, 1978;. The exact reason for this low amplitude is not known, but it is usually attributed to the vernix caseosa (a poor electrical conductor) which often covers the fetus at this gesta tion.…”

“…Since this interference affects 15-20% of the fetal signals (Wheeler et al, 1978) a loss of 30-40% of the genuine beat-to-beat information is in evitable. The "blanking" technique usually employed in commercial fetal monitors also removes fetal signals when they coincide with maternal complexes, so that pulses have to be substituted artificially to avoid underestimating the fetal heart rate by 50%.…”

Two‐dimensional and M‐mode echocardiographic evaluation of fetal arrhythmia

“…Monitoring fetal heart rate by ultrasonic and electrocardiographic techniques (Carretti et al, 1974;Carter et al, 1980;Liu et al, 1978;Rultgers et af., 1970;Schifrin, 1972;Wheeler et al, 1978) has been widely used for the determination of mean heart rate prior to and during labor. However, the evaluation of fetal cardiac arrhythmia requires precise beat-to-beat analysis if an accurate diagnosis is to be made and potential fetal compromise avoided (Liu et al, 1978).…”

“…Although both indirect abdominal electrocardiography and direct recording after placement of fetal scalp electrode have been of some assistance, the quality of recordings in the former and invasiveness and timing in the latter limit their usefulness (Carretti et a l . , Carter et al, 1980;Schifrin, 1972;Wheeler et al, 1978). The advent of two-dimensional real time ultrasound has opened new areas in fetal cardiac research, especially in the screening of high-risk pregnant women (DeVore et al., 1983;Kleinman etal., 1980); at the same time M-mode echocardiograph has been used to evaluate arrhythmia in older cardiac patients (D'Cruz et al, 1977;Fujii et al 1978;Petsas et al, 1974;Prabhu et al, 1978;Procacci et al, 1978;Spilkin et al, 1977;Zoneraich et al, 1975).…”