Should every embryo undergo preimplantation genetic testing for aneuploidy? A review of the modern approach to in vitro fertilization.

Aneuploid conceptions constitute the majority of pregnancy failures in women of advanced maternal age. The best way to combat age-related decline in fertility is through preimplantation genetic testing for aneuploidy (PGT-A). PGT-A allows for better embryo selection, which improves implantation rates with single embryo transfer and reduces miscarriage rates. Single embryo transfers decrease multiple gestations and adverse pregnancy outcomes such as preterm or low birth weight infants. Advancements in extended embryo culture, blastocyst biopsy techniques, and 24-chromosome aneuploidy screening platforms have made PGT-A safe and accessible for all patients who undergo in vitro fertilization. Improved genomic coverage of new sequencing platforms, such as next-generation sequencing, has increased the identification and diagnosis of mosaicism and partial aneuploidies in preimplantation embryos. Mosaic embryos have decreased viability compared to euploid embryos when transferred, but some mosaic embryos result in normal live births. Whole genome amplification artifacts may contribute to a misdiagnosis of mosaicism, or some mosaic embryos may self-correct to euploid after implantation. For this reason, patients without euploid embryos should be given the option of transferring mosaic embryos after genetic counseling. Further research is needed to characterize which mosaic embryos may be viable.