Current status
The greatest advantage of PGT for aneuploidy (PGT-A) is its increase in promoting a single embryo transfer. Medical evidence supports pregnancy outcomes equivalent from a single euploid embryo transfer versus a double “untested” embryo transfer.
Only a handful of randomized, controlled trials have evaluated the efficacy of PGT-A. Outcomes have favored improved live birth rates; however, criticism exists for enrolling only good prognosis patients given their high likelihood of developing blastocyst embryos to biopsy. The only trial that used an “intention to treat” protocol (rather than randomization at the time of biopsy) did not demonstrate any difference in live birth or miscarriage comparing embryo selection by PGT-A versus embryo morphology alone. However, post hoc analysis did show a benefit with PGT-A in the 35- to 40-year-old age group, not in the less than 35-year-old group. All other trials demonstrated a reduction in miscarriage with PGT-A but only as a secondary outcome.
The medical literature does not support PGT-A to manage patients with recurrent pregnancy loss and there is no evidence for improvement in women aged less than 35 years or egg donors (F&S Reports. 2021;2:36-42). PGT-A has been effective in patients wishing family balancing.
Controversy
Enthusiasm for PGT-A is countered by lingering concerns. Trophectoderm cells are not in 100% concordance with the inner cell mass, which presumably explains the reports of chromosomally normal live births from the transfer of aneuploid embryos. Biopsy techniques among embryologists are not standardized. As a result, damage to the embryo has been raised as a possible explanation for equivalent pregnancy rates in studies showing no superiority of PGT-A in pregnancy outcome, although this point has recently been refuted.
PGT-A also embraces the “blast-or-bust” credo whereby no embryo transfer occurs unless a blastocyst embryo develops. This continues to beg the unanswerable question – would a woman who did not develop a blastocyst embryo for potential biopsy still conceive if she underwent a day 3 cleavage stage embryo transfer?
Future
Exciting iterations are encroaching for PGT 3.0. One method is blastocyst fluid aspiration to obtain DNA suitable for analysis by molecular genetic methods. Another is noninvasive PGT whereby spent media from the embryo is analyzed using cell-free DNA. Concordance with inner cell mass is reasonably good (approximately 85%) but needs to improve. A major advantage is the biopsy skill set among embryologists is eliminated. A criticism of noninvasive PGT is the risk of false-positive results from contamination of aneuploid cell secretion by physiologic apoptotic cells. Confined placental mosaicism can also increase aneuploidy in cell-free DNA thereby contributing to false positives.
Conclusion
PGT-A is robust technology that appears to benefit women aged above 35 years but not the general infertile population. Error rates must be consistent among laboratories and be lowered. Regarding mosaic embryos, the American Society for Reproductive Medicine guidelines recommend offering another egg retrieval if only mosaic embryos are available and to only consider mosaic embryo transfer following extensive genetic counseling. Long-term effects of PGT-A on children are lacking. The Cochrane Database concluded there was insufficient evidence to make PGT-A routine.
So, the debate is clear and ongoing – universal versus discretionary use of PGT-A? As in all things of life, one size does not fit all, and PGT-A is no exception.
Dr. Trolice is director of Fertility CARE – The IVF Center in Winter Park, Fla., and professor of obstetrics and gynecology at the University of Central Florida, Orlando. Contact him at obnews@mdedge.com.