During pregnancy, the flow of oxygen and nutrients to the baby and the removal of carbon dioxide and other waste gases from the baby is achieved through the placenta. Adequate blood flow to and from the placenta, and in both the maternal and fetal circulations, is necessary in order for the baby to receive enough oxygen and for it to be able to expel carbon dioxide and other waste gases. Any alteration in placental function can lead to decreases in the delivery of oxygen to the baby, a condition known as fetal hypoxia. The motivation for monitoring the fetus during pregnancy is to recognize pathologic conditions, typically decreased oxygen saturation, with sufficient warning to enable intervention by the clinician before irreversible changes set in. Fetal heart rate (fHR) monitoring is a proven means of assessing fetal health during the antenatal period.

Currently, the only widely available instrumentation for producing these data is based on Doppler ultrasound. However, it suffers from major limitations, the most important being that energy is introduced into the uterus from the bulky transducer (containing the ultrasound generation and detection elements) and towards the fetus, thus it cannot be used for long term monitoring. Fetal scalp electrodes are also used for fetal electrocardiogram (fECG) monitoring, which is an invasive technique. The abdominal ECG (abdECG) recordings is a very promising field, since it offers several advantages over Doppler ultrasound; lightweight electrodes are used and it is simple to operate, even by the mothers themselves, therefore, can be used in the normal home environment (Fig.1). The procedure is non-invasive and can be used for long duration recordings.

Fig.1. An abdECG recording. M: mECG influence, F: fECG influence

The antepartum fECG is usually obtained through skin electrodes attached to the mother’s body. Unfortunately, the desired fetal heartbeat signals appear at the electrode output buried in an additive mixture of undesired disturbances, such as the mother’s heartbeat signal with extremely high amplitude, the noise caused by mother’s respiration and electronic equipment. Appropriate signal processing techniques are required in order to recover the fECG components from the corrupted potential recordings. The problem of fECG extraction is an interesting and challenging problem in biomedical engineering. Two major approaches exist in the analysis of fetal electrical activity from abdECG signals: (a) extraction of the fECG from the abdECG and, subsequently, identification of the fHR from it, or (b) direct extraction of the fHR.

The Unit of Medical Technology and Intelligent Information Systems (MedLab) has a big experience in that field. Several algorithms have been proposed for extraction of fHR from multichannel abdECG recordings [1-8]. At these moment, our research focus on the development of methodologies for monitoring the fetal cardiac health status during pregnancy, through ONLY effective and non-invasive monitoring of the abdECG recordings of the mother.

Fig.2 Recordings abdECG from leads placed on the pregnant.