Preimplantation genetic testing: a review of current modalities
In this review, we evaluate the different modalities of embryo genetic testing including preimplantation genetic testing for aneuploidy (PGT-A), for monogenic/single-gene abnormalities (PGT-M), and for chromosomal structural rearrangements (PGT-SR), with a clinical focus on indications, strengths, limitations, and testing parameters of each technique. Articles were obtained from PubMed and American College Obstetricians and Gynecologists and American Society Reproductive Medicine committee opinions. While some studies have suggested that PGT-A increases live births in women of advanced maternal age, a recent large randomized controlled trial has shown no benefit to PGT-A compared with morphology grading alone, including in the subgroup of women >35 years of age. Aneuploidy screening shortens the time to live birth in women with advanced maternal age. However, PGT-A is not without risk (false positive and false negative and “no read” results and embryonic damage), has significant financial cost, and should only be used in conjunction with genetic counseling and under the supervision of a qualified infertility subspecialist. PGT-A is most cost-effective among women ≥38 years of age. PGT-M and PGT-SR offer useful low-risk screening modalities for debilitating inherited disorders. Significant advances have been made in the ability to analyze human embryos for genetic abnormalities. Screening for monogenic and chromosomal structural abnormalities potentially eliminates disease transmission to subsequent generations. Optimization of these molecular techniques remains necessary to decrease the false positive rates. Additional study of embryo mosaicism is needed to clarify which embryos are appropriate for transfer.