Although the first finding that fetal cells can enter the maternal circulation was made more than a century ago, it is still unclear if this finding will be translated into a clinically useful diagnostic tool in the foreseeable future. However, significant progress has been made via the analysis of cell-free fetal DNA in maternal plasma/serum and clinical services are now already being offered for the determination of fetal rhesus D status and sex. Currently, however, this technology is really only suited for the analysis of fetal genetic loci completely absent from the maternal genome. The detection of more subtle fetal genetic traits, such as point mutations involved in Mendelian disorders (thalassaemia, cystic fibrosis), is considerably more complex. Preliminary reports indicate that the detection of fetal aneuploidies might be possible using epigenetically modified genes, e.g. maspin on chromosome 18. Additionally, an exiting recent development is that it might be feasible to detect Down syndrome via the quantitative assessment of placentally derived cell-free mRNA of chromosome-21-specific genes such as PLAC4.