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Why does the debate linger after 30 years?
The holy grail of assisted reproductive technology (ART) is the delivery of a healthy child. From the world’s first successful ART cycle of in vitro fertilization in 1978 (3 years later in the United States), the goal of every cycle is to provide the woman with an embryo that has the highest potential for implantation and, ultimately, a single live birth.
Embryo aneuploidy is a major factor in the success of human reproduction. As women age, aneuploidy is reported in less than 30% of women aged younger than 35 years but rises to 90% for those in their mid-40s. Intuitively and through randomized, controlled trials, chromosome testing of embryos is a reasonable approach toward improved cycle outcomes and allows for the transfer of a single euploid embryo.
Recently, the phrase “add-ons” has entered the vernacular of editorials on IVF. These additional procedures are offered to patients with the expectation of improving results, yet many have not been supported by rigorous scientifically controlled research trials, e.g., endometrial scratch, embryo glue, and time-lapse imaging of embryos. Where does preimplantation genetic testing (PGT) belong in the IVF armamentarium and why, after 30 years, are there two diametrically opposed views on its benefit? (We will not address testing for single gene defects or chromosome structural rearrangements.)
How did we get here?
The first iteration of PGT used fluorescence in situ hybridization to not only identify X-linked recessive diseases (Hum Genet. 1992;89:18-22) but also the most common chromosome disorders (13, 18, 21, X, Y) by removing one to two blastomere cells from a day 3 embryo (six- to eight-cell stage). Despite wide enthusiasm, the technique was eventually determined to reduce implantation by nearly 40% and was abandoned; presumably impairing the embryo by removing up to one-third of its make-up.
Because of extended embryo culture to the blastocyst stage along with the improved cryopreservation process of vitrification, the next generation of embryo analysis surfaced, what we now refer to as PGT 2.0. Currently, approximately five to six cells from the outer embryo trophectoderm are removed and sent to a specialized laboratory for 24-chromosome screening while the biopsied embryos are cryopreserved. Outcome data (aneuploidy rates, mosaicism) have been influenced by the evolution of genetic platforms – from array comparative genome hybridization to single-nucleotide polymorphism array, to quantitative polymerase chain reaction, to next-generation sequencing (NGS). The newest platform, NGS with high resolution, provides the most extensive degree of analysis by detecting unbalanced translocations and a low cut-off percentage for mosaicism (20%). The clinical error rate is approximately 1%-2%, improved from the 2%-4% of earlier techniques.
The phenomenon of mosaicism describes two distinct cell lines in one embryo (typically one normal and one abnormal) and is defined based on the percentage of mosaicism – currently, the lower limit is 20%. Embryos with less than 20%-30% mosaicism are considered euploid and those greater than 70%-80% are aneuploid. Of note, clinics that do not request the reporting of mosaicism can result in the potential discarding of embryos labeled as aneuploid that would otherwise have potentially resulted in a live birth. The higher the cut-off value for designating mosaicism, the lower the false-positive rate (declaring an embryo aneuploid when euploid). While there is no safe degree of mosaicism, most transfers have resulted in chromosomally normal infants despite a lower implantation rate and higher miscarriage rate.
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.
Why does the debate linger after 30 years?
Why does the debate linger after 30 years?
The holy grail of assisted reproductive technology (ART) is the delivery of a healthy child. From the world’s first successful ART cycle of in vitro fertilization in 1978 (3 years later in the United States), the goal of every cycle is to provide the woman with an embryo that has the highest potential for implantation and, ultimately, a single live birth.
Embryo aneuploidy is a major factor in the success of human reproduction. As women age, aneuploidy is reported in less than 30% of women aged younger than 35 years but rises to 90% for those in their mid-40s. Intuitively and through randomized, controlled trials, chromosome testing of embryos is a reasonable approach toward improved cycle outcomes and allows for the transfer of a single euploid embryo.
Recently, the phrase “add-ons” has entered the vernacular of editorials on IVF. These additional procedures are offered to patients with the expectation of improving results, yet many have not been supported by rigorous scientifically controlled research trials, e.g., endometrial scratch, embryo glue, and time-lapse imaging of embryos. Where does preimplantation genetic testing (PGT) belong in the IVF armamentarium and why, after 30 years, are there two diametrically opposed views on its benefit? (We will not address testing for single gene defects or chromosome structural rearrangements.)
How did we get here?
The first iteration of PGT used fluorescence in situ hybridization to not only identify X-linked recessive diseases (Hum Genet. 1992;89:18-22) but also the most common chromosome disorders (13, 18, 21, X, Y) by removing one to two blastomere cells from a day 3 embryo (six- to eight-cell stage). Despite wide enthusiasm, the technique was eventually determined to reduce implantation by nearly 40% and was abandoned; presumably impairing the embryo by removing up to one-third of its make-up.
Because of extended embryo culture to the blastocyst stage along with the improved cryopreservation process of vitrification, the next generation of embryo analysis surfaced, what we now refer to as PGT 2.0. Currently, approximately five to six cells from the outer embryo trophectoderm are removed and sent to a specialized laboratory for 24-chromosome screening while the biopsied embryos are cryopreserved. Outcome data (aneuploidy rates, mosaicism) have been influenced by the evolution of genetic platforms – from array comparative genome hybridization to single-nucleotide polymorphism array, to quantitative polymerase chain reaction, to next-generation sequencing (NGS). The newest platform, NGS with high resolution, provides the most extensive degree of analysis by detecting unbalanced translocations and a low cut-off percentage for mosaicism (20%). The clinical error rate is approximately 1%-2%, improved from the 2%-4% of earlier techniques.
The phenomenon of mosaicism describes two distinct cell lines in one embryo (typically one normal and one abnormal) and is defined based on the percentage of mosaicism – currently, the lower limit is 20%. Embryos with less than 20%-30% mosaicism are considered euploid and those greater than 70%-80% are aneuploid. Of note, clinics that do not request the reporting of mosaicism can result in the potential discarding of embryos labeled as aneuploid that would otherwise have potentially resulted in a live birth. The higher the cut-off value for designating mosaicism, the lower the false-positive rate (declaring an embryo aneuploid when euploid). While there is no safe degree of mosaicism, most transfers have resulted in chromosomally normal infants despite a lower implantation rate and higher miscarriage rate.
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.
The holy grail of assisted reproductive technology (ART) is the delivery of a healthy child. From the world’s first successful ART cycle of in vitro fertilization in 1978 (3 years later in the United States), the goal of every cycle is to provide the woman with an embryo that has the highest potential for implantation and, ultimately, a single live birth.
Embryo aneuploidy is a major factor in the success of human reproduction. As women age, aneuploidy is reported in less than 30% of women aged younger than 35 years but rises to 90% for those in their mid-40s. Intuitively and through randomized, controlled trials, chromosome testing of embryos is a reasonable approach toward improved cycle outcomes and allows for the transfer of a single euploid embryo.
Recently, the phrase “add-ons” has entered the vernacular of editorials on IVF. These additional procedures are offered to patients with the expectation of improving results, yet many have not been supported by rigorous scientifically controlled research trials, e.g., endometrial scratch, embryo glue, and time-lapse imaging of embryos. Where does preimplantation genetic testing (PGT) belong in the IVF armamentarium and why, after 30 years, are there two diametrically opposed views on its benefit? (We will not address testing for single gene defects or chromosome structural rearrangements.)
How did we get here?
The first iteration of PGT used fluorescence in situ hybridization to not only identify X-linked recessive diseases (Hum Genet. 1992;89:18-22) but also the most common chromosome disorders (13, 18, 21, X, Y) by removing one to two blastomere cells from a day 3 embryo (six- to eight-cell stage). Despite wide enthusiasm, the technique was eventually determined to reduce implantation by nearly 40% and was abandoned; presumably impairing the embryo by removing up to one-third of its make-up.
Because of extended embryo culture to the blastocyst stage along with the improved cryopreservation process of vitrification, the next generation of embryo analysis surfaced, what we now refer to as PGT 2.0. Currently, approximately five to six cells from the outer embryo trophectoderm are removed and sent to a specialized laboratory for 24-chromosome screening while the biopsied embryos are cryopreserved. Outcome data (aneuploidy rates, mosaicism) have been influenced by the evolution of genetic platforms – from array comparative genome hybridization to single-nucleotide polymorphism array, to quantitative polymerase chain reaction, to next-generation sequencing (NGS). The newest platform, NGS with high resolution, provides the most extensive degree of analysis by detecting unbalanced translocations and a low cut-off percentage for mosaicism (20%). The clinical error rate is approximately 1%-2%, improved from the 2%-4% of earlier techniques.
The phenomenon of mosaicism describes two distinct cell lines in one embryo (typically one normal and one abnormal) and is defined based on the percentage of mosaicism – currently, the lower limit is 20%. Embryos with less than 20%-30% mosaicism are considered euploid and those greater than 70%-80% are aneuploid. Of note, clinics that do not request the reporting of mosaicism can result in the potential discarding of embryos labeled as aneuploid that would otherwise have potentially resulted in a live birth. The higher the cut-off value for designating mosaicism, the lower the false-positive rate (declaring an embryo aneuploid when euploid). While there is no safe degree of mosaicism, most transfers have resulted in chromosomally normal infants despite a lower implantation rate and higher miscarriage rate.
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.