Natalie Miroballi

Introduction. Infertile individuals often seek assisted reproductive technology (ART) to aid in conception, the most common of which is In vitro fertilization (IVF) therapy. The success rate of IVF is highly variable and depend on several clinical factors including the underlying causes of infertility and the woman’s age. The preimplantation development of embryos is naturally prone to developmental errors due to chromosomal abnormalities, evidenced by the large percentage of first trimester miscarriages. A healthy embryo contains 23 chromosomes; however, some embryos contain an abnormal number of chromosomes, a condition otherwise known as aneuploidy. Chromosomal errors can prevent embryo implantation into the uterus or result in early pregnancy abortion. Therefore, current IVF therapy includes screening embryonic DNA via pre-implantation genetic testing for aneuploidy (PGT-A). Genetic testing for aneuploidy entails whole gene amplification, next-generation sequencing (NGS) for chromosomal analysis, and data analysis/interpretation.¹ Based on the chromosomal analysis, embryos with 100% euploidy are selected for implantation. Current standards of obtaining DNA for genetic testing requires biopsy of cells from the trophectoderm (TE) layer of the blastocyst.² The TE biopsy method is invasive, labor intensive, and subject to inconsistencies and sampling biases.³ Scientists and physicians are transitioning from invasive methods to novel approaches utilizing minimally invasive pre-implantation genetic testing for aneuploidy (miPGT-A). Methods. Groups are studying the potential of using cell-free embryonic nuclear DNA (cfeDNA) found in spent embryonic media as a source for PGT-A analysis. The study “used donated human blastocytes that had previously undergone TE biopsy testing by an outside laboratory as part of clinical care of the IVF patient.”⁴ The blastocytes were thawed and individually cultured in culture media. The media was then isolated, amplified, and underwent NGS to test for aneuploidy. Results. The genetic analysis of the miPGT-A compared to embryo TE-biopsy were comparable. The miPGT-A method had a 93.8% concordance for embryo ploidy, which was 10% more accurate the TE-biopsy method. After adjusting the threshold for mosaicism, the false negative rate was 0% and the false positive rate was less than TE-biopsy rate⁴  Conclusion. The results indicate miPGT-A has proven to be a potential alternative to current invasive standards. However, the current methods lack consistency and reproducibility. Future studies should focus on optimizing the quality and source of the DNA for amplification, and clinical trials should document embryos screened with miPGT-A from implantation to successful delivery to confidently confirm the validity of the minimally invasive screening method.

1.  Munné, S., Spinella, F., Grifo, J., Zhang, J., Parriego Beltran, M., Fragouli, E., & Fiorentino, F. Clinical outcomes after the transfer of blastocysts characterized as mosaic by high resolution Next Generation Sequencing- further insights. European Journal of Medical Genetics, (2020); 63(2): 103741. doi.org/10.1016/j.ejmg.2019.103741.
2. Popovic, M., Dhaenens, L., Taelman, J., Dheedene, A., Bialecka, M., De Sutter, P., Chuva de Sousa Lopes, S. M., Menten, B., & Heindryckx, B. Extended in vitro culture of human embryos demonstrates the complex nature of diagnosing chromosomal mosaicism from a single trophectoderm biopsy. Human Reproduction, 2019; 34(4): 758–769. doi.org/10.1093/humrep/dez012.
3. Huang, L., Bogale, B., Tang, Y., Lu, S., Xie, X. S., & Racowsky, C. Noninvasive preimplantation genetic testing for aneuploidy in spent medium may be more reliable than trophectoderm biopsy. Proceedings of the National Academy of Sciences of the United States of America, 2019;116(28):14105–14112. doi.org/10.1073/pnas.1907472116.
4. Xu, J., Fang, R., Chen, L., Chen, D., Xiao, J.-P., Yang, W., Wang, H., Song, X., Ma, T., Bo, S., Shi, C., Ren, J., Huang, L., Cai, L.-Y., Yao, B., Xie, X. S., & Lu, S. Noninvasive chromosome screening of human embryos by genome sequencing of embryo culture medium for in vitro fertilization. Proceedings of the National Academy of Sciences, 2016; 113(42): 11907–11912. doi.org/10.1073/pnas.1613294113
5. Kuznyetsov, V., Madjunkova, S., Abramov, R., Antes, R., Ibarrientos, Z., Motamedi, G., Zaman, A., Kuznyetsova, I., & Librach, C. L. Minimally Invasive Cell-Free Human Embryo Aneuploidy Testing (miPGT-A) Utilizing Combined Spent Embryo Culture Medium and Blastocoel Fluid –Towards Development of a Clinical Assay. Scientific Reports, 2020; 10(1): 7244. doi.org/10.1038/s41598-020-64335-3.