The effect of changes in the conductive medium on the fetal ECG throughout gestation.

The electrical conduction of the ECG from the fetal heart to the maternal abdomen has been modelled by using volume conductor models based on the measured actual geometry. The models have been verified by means of multi-lead recordings of the fetal ECG. The results show that early in pregnancy (less than 28 weeks) the conduction can successfully be described by an electrically homogeneous model. Based on this model, a description of the fetal ECG that is independent of the position of the fetus is derived. In late pregnancies, the conduction is dominated by the isolating effect of the vernix caseosa. As the distribution of the vernix over the fetal body is unknown, the shape of the fetal ECG is disturbed in an unintelligible way. As a consequence, caution has to be applied when using the shape of the fetal ECG for diagnostic means.