A fetal electrocardiographic electrode.

A FETAL ELECTROCARDIOGRAPHIC ELECTRODEt Although it is sixty years since the first fetal electrocardiogram (FECG) was recorded by Cremer,1 it is only in recent years that attempts have been made to improve the FECG signal-to-noise ratio so that FECG configuration changes can be evaluated and the FECG used as a reliable trigger for automatic fetal heart rate (FHR) counting circuits. While the FECG signal-to-noise ratio can be improved by group averaging a number of consecutive FECG complexes with a digital computer,"' the most direct method is to attach an electrode directly to the fetus by either the trans-abdominal or transcervical routes." Unfortunately, the difficulties and hazards of these procedures limit their use to research. Some seven years ago, an electrode was made from a wound clip, insulated, and attached to the fetal presenting part.' This was applied after rupture of the membranes, with the cervix at least 2 cm. dilated and the presenting part no higher than a-2 station. With this electrode, it has been possible to accumulate a sizeable body of research and clinical data on the FECG and FHR patterns that was previously not available. Currently , the construction of the electrode is being revised with newer insulating materials. While the statistical evaluation of the revised FECG electrode is not yet complete, the marked improvement in FECG signal-to-noise ratio obtained with these electrodes has so improved FHR monitoring techniques that they will be described at this time. Our earlier FECG electrodes usually provided signals of 50 to 75 microvolts in amplitude. With the revised electrode, FECG's are usually in the range of 300 to 500 microvolts and signals as high as 800 microvolts have been recorded. As a result, there is a pronounced improvement in the FECG signal-to-noise ratio so that the details of the FECG baseline can be identified clearly and an almost artefact-free plot of FHR obtained throughout labor and delivery.