External Cardiotocography (CTG) is one of the most widespread diagnostic methods in clinical practice for checking foetal conditions both in the ante- and intra-partum period. However, even though it has legal value in Italy and in some other countries, it lacks of objectivity and reproducibility because of its dependence on observer's expertise and training. In order to overcome these limitations, more objective methods for CTG interpretation have been proposed in recent years. In particular, many developed techniques aim to assess the foetal heart rate variability (FHRV), since its demonstrated relationship with the foetal Autonomous Nervous System functional state. The aim of the present work is to deepen the FHRV analysis through the Symbolic Dynamics Analysis (SDA), a nonlinear technique - already applied with positive results to the adults and, in some cases, to the foetus - which allows a simple description of a system’s dynamics by means of a limited amount of symbols and proper classification schemes. Thanks to its simplicity of interpretation, it could be a useful tool for clinicians in foetal monitoring.