# Compact long-term recorder for the transabdominal foetal and maternal elect rocard iog ram J. F. Pieri I J.A. Crowe I B.R. Hayes-Gill I C.J. Spencer 2 K. Bhogal 2 D. K. James 2 1School of Electrical & Electronic Engineering, University of Nottingham, Nottingham, UK 2School of Human Development, University of Nottingham, Queens Medical Centre, Nottingham, UK Abstract--Foetal heart rate (FHR) monitoring is a proven means of assessing foetal health during the antenatal period. Currently, the only widely available instrumenta- tion for producing these data is based on Doppler ultrasound, a technology that is unsuitable for long-term use. For nearly a century, it has been known that the foetal electrocardiogram (FECG) can be detected using electrodes placed on the maternal abdomen. Although these signals suggest an alternative means of FHR derivation, their use has been limited owing to problems of poor signal-to-noise ratio. However, the eminent suitability of the transabdominal FECG for long-term FHR monitoring has suggested that perseverance with the technique would be worthwhile. The paper describes the design, construction and use of a compact, long-term recorder of three channels of 24 h antenatal transabdominal data. Preliminary use of the recorder in around 400 short recording sessions demonstrates that FHR records of equivalent quality to those from Doppler ultrasound-based instruments can be extracted from such data. The success of FHR derivation is, on average, around 65% of the recording period from around 20 weeks gestation (although this figure is reduced from around 28-32 weeks, and the success rates exhibit a wide range when individual subjects are considered). These results demonstrate that the technique offers, not only a means of acquiring long-term FHR data that are problematic to obtain by other means, but also a more patient-friendly alternative to the Doppler ultrasound technique. Keywords--Foetal monitoring, Antenatal, Foetal electrocardiogram, Foetal heart rate, Maternal heart rate, Electrophysiological recorder Med. Biol. Eng. Comput., 2001, 39, 118-125 J 1 Introduction DURINGPREGNANCY, the inaccessibility of the foetus means that the only physiological parameter that can be monitored non- invasively on a routine basis is heart rate. Fortunately, the analysis of these data provides clinically valuable information, and so the technique is widely used for both routine monitoring and more regular assessment of foetuses considered at risk. Currently, virtually all foetal heart rate (FHR) data are obtained using the Doppler ultrasound technique. However, despite its domination, it has a number of disadvantages. Being an active technique, the question of the safety of insonating the foetus is a recurring issue, with the bulky transducer (containing the ultrasound generation and detection elements) also having relatively large power requirements, in addition, it must be held in position by an elasticated belt that is found uncomfortable by the mothers being monitored and it must be continually repositioned to ensure that the foetal heart Correspondence should be addressed to Dr J. Crowe; e-marl: john. crowe@nottingham.ac.uk First received 19 April 2000 and in final form 1 November 2000 MBEC online number: 20013538 © IFMBE:2001 118 falls within the ultrasound beam's path. Also, only averaged heart rate, rather than RR interval data, is provided (MORGENSTERN, 1996), and it is well known that, under certain conditions, erroneous heart rate patterns are obtained (DAWES et al., 1990). In summary, although widely and successfully used for routine bedside antenatal monitoring, the current Doppler ultrasound-based monitors nevertheless leave room for improvement in this role, and the technique is wholly unsuitable for long-term ambulatory use. Alternative means of antenatal FHR monitoring include foetal magnetocardiography, phonocardiography and electrocardio- graphy. The foetal magnetocardiogram (PETERS et al., 1998), detectable using SQUiD-based magnetometers, enables the acquisition of beat-to-beat FHR data and foetal magnetocardio- gram (FMCG) waveforms from the 13th week of pregnancy, both of which are of value in assessing foetuses with known cardiac abnormalities. However, its requirements of costly, sensitive and bulky instrumentation, which must be operated in a low-noise environment by skilled personnel, render it inconvenient for routine bedside use and obviously not suitable for ambulatory use. Derivation of FHR from the foetal phonocardiogram has been demonstrated, but, although low-cost and simple to use, it suffers from the breakthrough of non-foetal heart sounds into Medical & Biological Engineering & Computing 2001, Vol. 39