During gestation, the maternal organism, the foetus and the placenta are subjected to multiple reciprocal interactions (Maurel et Kanellopoulos, 2008). The existence of cellular exchanges between the mother and the foetus are now well established, and the search of foetal male cells or of HLA antigens specific of the foetus are the two strategies used to detect cellular traffic. PCR and RT-PCR experiments performed on the sequences or the genes specific of the foetus or the mother - using murine models - have made it possible to establish that these events are frequent. Nevertheless, only the development of techniques allowing to reach extremely precise detection levels will lead to envisage non-invasive prenatal diagnostics so as to detect possible deficiencies or immunological incompatibilities. The aim of our studies performed in collaboration with the group of Colette Kanellopoulos (UMR 7592) consists in selecting foetal cells thanks to aptamers identified as specific markers of these cells. Such aptamers will allow affinity purification of the foetal cells, and after crosslink the caracterisation of the proteins recognized by the aptamers.