Impact of polar body biopsy on embryo morphokinetics-back to the roots in preimplantation genetic testing?

Polar Body Biopsy Helps in Reducing the Total Pregnancy Loss Rates in Intracytoplasmic Sperm Injection Cycles

OBJECTIVE

 To evaluate the effect of polar body biopsy (PBB) on pregnancy and pregnancy loss outcomes in intracytoplasmic sperm injection (ICSI) cycles.

METHODOLOGY

This is a retrospective case-control study that analyzed 147 ICSI embryo transfer (ET) cycles. The study included 82 subfertile patients (31 patients with ICSI and PBB therapy = case group; 51 patients with ICSI without the PBB therapy = control group). We conducted a statistical analysis of all pregnancies and births resulting from fresh and thawed ICSI cycles, with and without the use of PBB after a single embryo transfer (SET) of a blastocyst (BL). Our main outcome measures were the pregnancy and pregnancy outcome rates after ICSI with and without the PBB.

RESULT

 The implantation rate in the ICSI with PBB group was lower than in the ICSI without PBB group, but there were no significant differences (11 = 17.50% vs. 21 = 25.00%, RR = 0.63, 95% CI: 0.28-1.44, p = 0.37). The yolk sac detection rate in the ICSI with PBB group was lower than in the ICSI without PBB group, but there were no significant differences (8 = 12.70% vs. 16 = 19.00%, RR = 0.62, 95% CI: 0.25-1.55, p = 0.65). The fetal heartbeat rate in the ICSI with PBB group was lower than in the ICSI without PBB group, but there were no significant differences (7 = 11.10% vs. 12 = 14.30%, RR = 0.75, 95% CI: 0.28-2.03, p = 0.75). The live birth rate in the ICSI with PBB group was higher than in the ICSI without PBB group, but there were no significant differences (5 = 7.90% vs. 5 = 6.00%, RR = 1.36, 95% CI: 0.37-4.92, p = 0.88). The total pregnancy loss rate was significantly lower in the ICSI with PBB group than in the ICSI without PBB group (6 = 9.50% vs. 19 = 22.60%, RR = 0.36, 95% CI: 0.14-0.96, p = 0.04).

CONCLUSION

 A bigger patient sample is needed for further evaluation, but based on our findings, we recommend the PBB in the cases of apparent or suspected genetic, maternal diseases and/or aneuploidies and for improving general ICSI outcomes, through the reduction of pregnancy loss rates. This information can support reproductive professionals and embryologists who are looking to invest in new solutions for their centers and labs.

Clinical application of polar body-based preimplantation genetic testing for maternal mutations in women with a limited number of oocytes

BACKGROUND

Trophectoderm (TE) cell biopsy at the blastocyst stage is currently the most common method used in preimplantation genetic testing for monogenic disorders (PGT-M). However, this approach may result in the wasting of some genetically unaffected embryos because only a proportion of zygotes develop to the blastocyst stage. Unaffected embryos, which degenerated during blastomere-blastocyst transformation, may give birth if transferred before the blastocyst stage and may be of great value to women with a low oocyte count. This study sought to investigate the potential application of polar-body (PB) biopsy in saving more genetically unaffected embryos for women with disease-causing mutations and a limited number of oocytes during PGT-M.

METHODS

Three couples with female partners who had autosomal dominant or X-linked mutations in IRF6, FMR1, and EDA were recruited. The number of retrieved oocytes was limited to six per cycle. The first and second PBs (PB1 and PB2) of each oocyte were biopsied separately and subjected to multiple displacement amplification (MDA). The genotype of each embryo was determined by analyzing the MDA products of the corresponding PB1 and PB2 using a novel approach that combined direct mutation testing and single nucleotide polymorphism linkage analysis. Mutation-free embryos cryopreserved before the blastocyst stage were chosen for transfer.

RESULTS

In total, four cycles were performed, resulting in the retrieval of 15 oocytes for three couples. The genotype of each embryo was successfully determined. Seven mutation-free embryos were discovered. Three of them were transferred, resulting in two clinical pregnancies, and the birth of two healthy infants. The accuracy of the embryo genotypes was validated by genetic testing of fetuses in the second trimester or at birth.

CONCLUSIONS

The PB-based strategy is feasible and effective for determining the mutation-carrier statuses of embryos in PGT-M for maternal mutations. Compared to blastocyst stage detection, this method may save a greater number of genetically unaffected embryos for patients. Further clinical trials are needed to determine whether PB biopsy is more beneficial than TE cell biopsy for women with disease-causing mutations and a limited number of oocytes in PGT-M.

Polar body-based PGT-A: not dead yet? A step forward back to the roots of PGT-A

Trophectoderm-based preimplantation genetic testing for aneuploidies (PGT-A) is used worldwide as a means of selecting embryos with high potential for achieving a live birth. However, trophectoderm analysis may be impaired through embryonic mosaicism, leading to genetically healthy embryos being falsely discarded, and thus even reducing cumulative live birth rates. Polar body biopsy, a technique applied since the early days of preimplantation testing, has been abandoned by most IVF centres. In comparison to trophectoderm analysis, however, polar body biopsy might even have certain advantages over trophectoderm PGT-A. This Countercurrent contribution discusses the newest clinical evidence, as well as ethical and cost-efficiency considerations, and argue that polar body analysis should be reconsidered.

Preimplantation genetic testing: A narrative review

Preimplantation genetic testing (PGT) is a diagnostic procedure that has become a powerful complement to assisted reproduction techniques. PGT has numerous indications, and there is a wide range of techniques that can be used, each with advantages and limitations that should be considered before choosing the more adequate one. In this article, it is reviewed the indications for PGT, biopsy and diagnostic technologies, along with their evolution, while also broaching new emerging methods.

Evolution of Minimally Invasive and Non-Invasive Preimplantation Genetic Testing: An Overview

Preimplantation genetic testing (PGT) has become a common supplementary diagnοstic/testing tοol for in vitro fertilization (ΙVF) cycles due to a significant increase in cases of PGT fοr mοnogenic cοnditions (ΡGT-M) and de novο aneuplοidies (ΡGT-A) over the last ten years. This tendency is mostly attributable to the advancement and application of novel cytogenetic and molecular techniques in clinical practice that are capable of providing an efficient evaluation of the embryonic chromosomal complement and leading to better IVF/ICSI results. Although PGT is widely used, it requires invasive biopsy of the blastocyst, which may harm the embryo. Non-invasive approaches, like cell-free DNA (cfDNA) testing, have lower risks but have drawbacks in consistency and sensitivity. This review discusses new developments and opportunities in the field of preimplantation genetic testing, enhancing the overall effectiveness and accessibility of preimplantation testing in the framework of developments in genomic sequencing, bioinformatics, and the integration of artificial intelligence in the interpretation of genetic data.

Impact of maternally derived meiotic aneuploidies on early embryonic development in vitro

PURPOSE

To assess early embryonic developmental potential of embryos affected by maternally inherited meiotic aneuploidies.

METHODS

This observational, descriptive study includes 930 oocytes from 151 patients which were retrospectively analyzed by combining the morphological assessment with the genetic results from polar body diagnosis.

RESULTS

Of 930 oocytes examined, 566 (60.9%) were tested aneuploid. Developmental potential until cleavage stage was not affected by trisomies or monosomies (69.6% vs. 77.1%, p = 0.75). However, trisomies significantly more often resulted in top quality cleavage stage embryos compared to monosomies (20% vs. 17.6%, p =  < 0.01). Top quality blastocysts were more likely to be euploid than aneuploid (52.4% vs. 47.6%, p = 0.032). Additionally, significantly more aneuploid embryos resulted in developmental arrest compared to euploid embryos (15.3% vs. 6.7%, p = 0.003). Overall, there was no significant difference in the frequency of trisomies and monosomies in blastocyst stage embryos. (28.3% vs. 28.2%; p = 0.81). In contrast to earlier developmental stages, distribution of trisomies and monosomies did not differ in top quality blastocysts (8.3% vs. 5.3%, p = 0.32). However, certain chromosomal abnormalities showed a higher potential to develop into a top-rated blastocyst. These included monosomies 2, 5, 8, 10, 16, 17, 20, 21, and 22 and trisomies 2, 4, 5, 8, 9, 10, 11, 12, 13, 16, 17, 18 and 20.

CONCLUSION

Meiotically induced maternal aneuploidies have different effects on early embryonic development. While no difference in developmental potential between monosomies and trisomies could be observed in blastocysts, cleavage stage quality was significantly affected by chromosomal aneuploidies.

Novel Time-Lapse Parameters Correlate with Embryo Ploidy and Suggest an Improvement in Non-Invasive Embryo Selection

Selecting the best embryo for transfer is key to success in assisted reproduction. The use of algorithms or artificial intelligence can already predict blastulation or implantation with good results. However, ploidy predictions still rely on invasive techniques. Embryologists are still essential, and improving their evaluation tools can enhance clinical outcomes. This study analyzed 374 blastocysts from preimplantation genetic testing cycles. Embryos were cultured in time-lapse incubators and tested for aneuploidies; images were then studied for morphokinetic parameters. We present a new parameter, "st₂, start of t₂", detected at the beginning of the first cell cleavage, as strongly implicated in ploidy status. We describe specific cytoplasmic movement patterns associated with ploidy status. Aneuploid embryos also present slower developmental rates (t₃, t₅, t_SB, t_B, cc3, and t₅-t₂). Our analysis demonstrates a positive correlation among them for euploid embryos, while aneuploids present non-sequential behaviors. A logistic regression study confirmed the implications of the described parameters, showing a ROC value of 0.69 for ploidy prediction (95% confidence interval (CI), 0.62 to 0.76). Our results show that optimizing the relevant indicators to select the most suitable blastocyst, such as by including st₂, could reduce the time until the pregnancy of a euploid baby while avoiding invasive and expensive methods.

The second polar body contributes to the fate asymmetry in the mouse embryo

The polar bodies (PBs) are extruded microcells during oocyte meiosis and generally regarded as inessentials for embryonic development. Therefore, PBs have been widely used as important materials for pre-implantation genetic diagnosis in human. Here we report that the second PB (PB2) in the mouse zygote may play roles in cell-fate specification and post-implantation development. A subset of mRNAs encoding pluripotency-related factors are enriched in PB2. Nascent proteins may be synthesized in PB2 after fertilization and transport from PB2 to the zygote before the two-cell stage. The PB2-attached blastomere (pbB) at the two-cell stage, compared to the other blastomere (npbB), likely contributes more descendants to the inner cell mass (ICM) lineage in the blastocyst. Removal of PB2 from the zygote or transient blockage of material exchange between PB2 and the zygote by nocodazole treatment appears to cause a loss of the ICM fate bias of pbB. PB2 removal or nocodazole treatment also results in abnormal post-implantation development. Injection of PB2 lysate into pbB of PB2-removed two-cell-stage embryos may reset the cell-fate preference and rescue post-implantation development. Our data collectively suggest that PB2 would demarcate the earliest cell-fate asymmetry of the mouse zygote and be required for post-implantation development.