Abstract: The invention provides an in vitro method for non-invasive preimplantation assessment of an embryo by comprising amplifying and detecting a nucleic acid sequence of interest indicative of a genetic deficiency from a sample taken from the in vitro culture medium of the embryo and assessing the embryo as having a genetic deficiency if the presence of the sequence of interest is detected in the in vitro culture medium of the embryo. The examples show the detection of SNPs relating to the genes MDR1 and prothrombin and the SNP responsible for the Leiden syndrome. The application also mentions the possibility of establishing short tandem repeat (STR) marker profiles of DNA in the culture medium and full genome sequencing of the DNA in the culture medium as a means for determining embryo quality.