Blastocoel fluid as an alternative source of DNA for minimally invasive PGT and biomarker of embryo competence.

The discovery of DNA in blastocoel fluid (BF-DNA) generated new perspectives in the potential development of simpler and safer alternative non-invasive tests in reproductive genetics. Short DNA fragments of apoptotic origin, together with specific expression patterns of pro- and anti-apoptotic genes in the blastocoel fluid of euploid and aneuploid embryos, suggest a self-correction mechanism to preferentially eliminate aneuploid cells, and purge defective and non-viable cells. The correlation of blastocoel fluid content with the genetic status of the whole embryo, and therefore its potential use in minimally invasive preimplantation genetic testing (miPGT), or as an indicator of embryo potential, remains uncertain and needs to be determined. The limited amount and compromised integrity of BF-DNA, with likely apoptotic origination, constrains its amplification, leading to low concordance and reproducibility rates for both aneuploidy screening and monogenic testing. While embryo genotyping constitutes a more ambitious goal, the presence of analysable DNA after amplification in blastocoel fluid may be used as a clinical biomarker of embryo competency to select the most viable embryo(s) for transfer, and potentially improve the implantation rate. Although blastocentesis remains a promising area for future research, several technical and methodological limitations are currently constraining its consideration for clinical practice.