“No diagnosis” embryos after PGS should not be discarded: rebiopsy and reanalysis demonstrate the majority are euploid

Multiple embryo manipulations in PGT-A cycles may result in inferior clinical outcomes

RESEARCH QUESTION

Do embryos that undergo a thaw, biopsy and re-vitrification (TBR) for pre-implantation genetic testing for aneuploidy (PGT-A) have different ploidy and transfer outcomes compared with fresh biopsied embryos?

DESIGN

Retrospective cohort study of all embryos that underwent the following procedures: fresh biopsy for PGT-A (fresh biopsy); embryos that were warmed, biopsied for PGT-A and re-vitrified (single biopsy TBR); embryos with a no signal result after initial biopsy that were subsequently warmed, biopsied and re-vitrified (double biopsy TBR). The patients who underwent transfers of those embryos at a single academic institution between March 2013 and December 2021 were also studied.

RESULTS

About 30% of embryos planned for TBR underwent attrition. Euploidy rates were similar after biopsy: fresh biopsy (42.7%); single biopsy TBR (47.5%) (adjusted RR: 0.99, 0.88 to 1.12); and double biopsy TBR 50.3% (adjusted RR: 0.99, 0.80 to 1.21). Ongoing pregnancy over 8 weeks was not statistically significant (double biopsy TBR: 6/19 [31.6%] versus fresh biopsy: 650/1062 [61.2%]) (adjusted RR 0.52, 95% CI 0.26 to 1.03). The miscarriage rate increased (double biopsy TBR: 4/19 [21.1%] versus fresh biopsy: 66/1062 [6.2%])(RR 3.39, 95% CI 1.38 to 8.31). Live birth rate was also lower per transfer for the double biopsy TBR group (double biopsy TBR [18.75%] versus fresh biopsy [53.75%]) (RR 0.35, 95% CI 0.12 to 0.98), though not after adjustment (adjusted RR 0.37, 95% CI 0.13 to 1.09). These differences were not seen when single biopsy TBR embryos were transferred.

CONCLUSIONS

Embryos that undergo TBR have an equivalent euploidy rate to fresh biopsied embryos. Despite that, double biopsy TBR embryos may have impaired transfer outcomes.

Embryo drop-out rates in preimplantation genetic testing for aneuploidy (PGT-A): a retrospective data analysis from the DoLoRes study

PURPOSE

To evaluate the decline in transferable embryos in preimplantation genetic testing for aneuploidy (PGT-A) cycles due to (a) non-biopsable blastocyst quality, (b) failure of genetic analysis, (c) diagnosis of uniform numerical or structural chromosomal aberrations, and/or (d) chromosomal aberrations in mosaic constitution.

METHODS

This retrospective multicenter study comprised outcomes of 1562 blastocysts originating from 363 controlled ovarian stimulation cycles, respectively, 226 IVF couples in the period between January 2016 and December 2018. Inclusion criteria were PGT-A cycles with trophectoderm biopsy (TB) and next generation sequencing (NGS).

RESULTS

Out of 1562 blastocysts, 25.8% were lost due to non-biopsable and/or non-freezable embryo quality. In 10.3% of all biopsied blastocysts, genetic analysis failed. After exclusion of embryos with uniform or chromosomal aberrations in mosaic, only 18.1% of those originally yielded remained as diagnosed euploid embryos suitable for transfer. This translates into 50.4% of patients and 57.6% of stimulated cycles with no euploid embryo left for transfer. The risk that no transfer can take place rose significantly with a lower number of oocytes and with increasing maternal age. The chance for at least one euploid blastocyst/cycle in advanced maternal age (AMA)-patients was 33.3% compared to 52.1% in recurrent miscarriage (RM), 59.8% in recurrent implantation failure (RIF), and 60.0% in severe male factor (SMF).

CONCLUSIONS

The present study demonstrates that PGT-A is accompanied by high embryo drop-out rates. IVF-practitioners should be aware that their patients run a high risk of ending up without any embryo suitable for transfer after (several) stimulation cycles, especially in AMA patients. Patients should be informed in detail about the frequency of inconclusive or mosaic results, with the associated risk of not having an euploid embryo available for transfer after PGT-A, as well as the high cost involved in this type of testing.

Should embryo rebiopsy be considered a regular strategy to increase the number of embryos available for transfer?

PURPOSE

To investigate whether embryo rebiopsy increases the yield of in vitro fertilization (IVF) cycles.

METHODS

Retrospective study including 18,028 blastocysts submitted for trophectoderm biopsy and preimplantation genetic testing for aneuploidy (PGT-A) between January 2016 and December 2021 in a private IVF center. Out of the 517 embryos categorized as inconclusive, 400 survived intact to the warming procedure, re-expanded, and were suitable for rebiopsy. Of them, 71 rebiopsied blastocysts were transferred. Factors affecting the probability of obtaining an undiagnosed blastocyst and clinical outcomes from blastocysts biopsied once and twice were investigated.

RESULTS

The overall diagnostic rate was 97.1%, with 517 blastocysts receiving inconclusive reports. Several blastocyst and laboratory features, such as the day of the biopsy, the stage of development, and the biopsy methodology, were related to the risk of obtaining an inconclusive diagnosis after PGT-A. A successful diagnosis was obtained in 384 of the rebiopsied blastocysts, 238 of which were chromosomally transferable. A total of 71 rebiopsied blastocysts were transferred, resulting in 32 clinical pregnancies [(clinical pregnancy rate (CPR)=45.1%], 16 miscarriages [(miscarriage rate (MR)=41%], and, until September 2020, 12 live births [(live birth rate (LBR)=23.1%]. A significantly lower LBR and higher MR were obtained after transferring rebiopsied blastocysts compared to those biopsied once.

CONCLUSION

Although an extra round of biopsy and vitrification may cause a detrimental effect on embryo viability, re-analyzing the test-failure blastocysts contributes to increasing the number of euploid blastocysts available for transfer and the LBR.

Comment on the recent PGDIS Position Statement on the Transfer of Mosaic Embryos 2021

The worldwide demand of preimplantation genetic testing for aneuploidy (PGT-A) is still growing. However, chromosomal mosaic results greatly challenge the clinical practice. The recently published PGDIS Position Statement on the Transfer of Mosaic Embryos is the third PGDIS position statement on how to deal with embryos diagnosed as chromosomal mosaics (CM) and, one of many attempts of different societies and working groups to provide a guideline for clinicians, laboratories, clinics, and genetic counselors. But still, as in previous statements, many issues remained unresolved. Moreover, from our point of view, the question how to deal with embryos diagnosed as CM, consisting of two or more karyological cell lines cannot be separated from all the other aspects of PGT-A including its accuracy. The paucity of clearcut indications for PGT-A and evidence of benefit as well as an overall cost-benefit assessment is given below.

Blastocyst Vitrification and Trophectoderm Biopsy Cumulatively Alter Embryonic Gene Expression in a Mouse Model

Although embryo vitrification has been used extensively in human assisted reproductive technology (ART) and animal models, epidemiologic evidence and randomized controlled trials suggest differences in pregnancy/perinatal outcomes (birthweight, risk for preterm birth, and pre-eclampsia) between babies born from fresh versus frozen embryo transfers. To address the uncertainty surrounding the effects of laboratory manipulations of embryos on clinical outcomes, we subjected mouse blastocysts to increasing levels of manipulation for transcriptome analysis. Blastocysts were randomly divided into four groups: no manipulation (control), single vitrification/thaw (1 vit), double vitrification/thaw (2 vit), and single vitrification/thaw plus trophectoderm biopsy and again vitrified/thawed (2 vit + bx). Three sets of 15 blastocysts in each group were pooled for RNA sequencing, and differentially expressed genes (DEGs) and pathways were determined by statistical analysis. Blastocysts were also stained for ZO-1 and F-actin to assess cytoskeletal integrity. Freeze/thaw and biopsy manipulation affected multiple biological pathways. The most significant differences were detected in genes related to innate immunity, apoptosis, and mitochondrial function, with the magnitude of change proportional to the extent to manipulation. Significant disruptions were also seen in cytoskeletal staining, with greater disruptions seen with greater of manipulation. Our data suggests that embryo vitrification and biopsy affect embryo gene transcription, with several identified DEGs that may have plausible mechanisms for the clinical outcomes seen in human offspring following ART. Further study is required to determine whether these alterations in gene expression are associated with clinical differences seen in children born from fresh or frozen embryo transfer.

Consistency in rates of diagnosis of embryonic mosaicism, segmental abnormalities, and "no call" results among experienced embryologists performing preimplantation genetic testing for aneuploidy

OBJECTIVE

To determine whether differences exist in rates of subchromosomal abnormalities, mosaicism, and "no call" results among embryologists performing and loading trophectoderm biopsies for preimplantation genetic testing for aneuploidy (PGT-A).

DESIGN

Retrospective cohort.

SETTING

Large infertility center.

PATIENTS

All patients undergoing in vitro fertilization with PGT-A.

INTERVENTIONS

The NexCCS next generation sequencing platform was used for PGT-A. The χ2 testing assessed differences in rates of primary outcomes between embryologists. Intraclass correlation coefficients evaluated inter-embryologist reliability in rates of abnormal and no call results. Median absolute performance difference (MAPD) scores, which quantify the impact of technical variation on analytical performance, were averaged for individual embryologists. Analysis of variance assessed differences in mean MAPD scores.

MAIN OUTCOME MEASURES

Interoperator variability in rates of mosaic, segmental, and no call results.

RESULTS

Four embryologists performed 30,899 biopsies and 6 embryologists loaded specimens into designated tubes. Among individuals performing trophectoderm sampling, rates of mosaicism were 4.3% to 6.1%, segmental errors were 9.0% to 10.7%, and inconclusive results were 1.1% to 2.9%. For those loading, the incidence of mosaicism was 4.2% to 5.9%, subchromosomal abnormalities was 9.7% to 10.4%, and no call results was 1.2% to 2.2%. The intraclass correlation coefficient was 0.978 for embryologists performing biopsies and 0.981 for those loading. Differences in mean MAPD scores were within 0.6% and 0.2% of each other for doing biopsies and loading embryologists, respectively.

CONCLUSIONS

Rates of mosaicism, segmental, and no call PGT-A results are consistent among experienced embryologists. Due to the large sample size included, differences within 1% of the mean were deemed clinically irrelevant despite statistical significance.

When next-generation sequencing-based preimplantation genetic testing for aneuploidy (PGT-A) yields an inconclusive report: diagnostic results and clinical outcomes after re biopsy

PURPOSE

To describe diagnostic results following re-biopsy of blastocysts with inconclusive results on preimplantation genetic screening for aneuploidy (PGT-A) and to evaluate the reproductive potential of re-biopsied blastocysts.

METHODS

This retrospective cohort study included all trophectoderm biopsies submitted for PGT-A by a large in vitro fertilization center to a single genetics laboratory from June 2016 to October 2018. PGT-A was performed using next-generation sequencing (NGS). No-result blastocysts that underwent re-biopsy were subsequently classified as euploid, aneuploid, mosaic/segmental, or no-result. Ongoing pregnancy and clinical loss rates were assessed following transfer of re-biopsied blastocysts. Logistic regressions were conducted to account for age and blastocyst morphology.

RESULTS

Of the trophectoderm biopsies submitted for PGT-A, 635/25,199 (2.5%) were categorized as no-result. Those that underwent re-biopsy (n = 250) had a 95.2% diagnostic rate with 140 (56.0%) receiving euploid diagnoses. Thirty-six re-biopsied blastocysts deemed euploid were subsequently transferred, resulting in 18 (50.0%) ongoing pregnancies and 5 (13.9%) clinical losses. After adjusting for age and blastocyst morphology, there remained a lower ongoing pregnancy rate and a trend towards higher clinical loss rate following transfer of a re-biopsied blastocyst. When compared to blastocysts that underwent the same number of vitrification-warming cycles but only one biopsy, there were no differences in outcomes.

CONCLUSIONS

Failure to obtain an analytical result does not change the probability that a given blastocyst is euploid. Pregnancy outcomes following transfer of re-biopsied blastocysts are favorable, but further data must be accrued for an adequately powered comparison with outcomes after transfer of blastocysts biopsied once.

Practical Considerations in Providing Preimplantation Genetic Testing for Aneuploidies (PGT-A)

Preimplantation genetic testing for aneuploidies (PGT-A) has been controversial in its application to improve reproductive success, reduce time-to-pregnancy, and serve the intention-to-treat. Nevertheless, many in vitro fertilization (IVF) units have already introduced the service for one reason or another. Given PGT-A is not a stand-alone technique but a clinical service involving several disciplines, this mini review discussed the factors that can influence success rates when PGT-A is applied and highlighted practical issues encountered by clinicians, embryology, and genetics laboratories involved in the provision of PGT-A service.