Preimplantation genetic screening (PGS) for aneuploidies is currently performed by analyzing samples of 5-6 cells obtained by trophectoderm biopsy at the blastocyst stage. With the use of available molecular biology techniques, the chromosomal constitution of the cells sampled by the biopsy can be determined with a very high reliability. However, doubts are currently increasing as to the possibility of considering the results obtained with these small samples of trophectoderm cells as representative of the whole trophectoderm and, in a broader sense, of the inner cell mass which is the ultimate diagnosis target. Both empirical data and mathematical models converge to suggest that PGS, as performed nowadays, is prone to interpretation errors due to which normal embryos can actually be discarded and abnormal ones transferred. Here we suggest that using soluble DNA obtained by liquid biopsy (spent medium after blastocyst culture) merits further investigation as a viable solution to this problem.