O-020 Aneuploidy and mosaicism in human embryos: How correct detection may improve IVF clinical outcomes

Study question

Can new next-generation sequencing (NGS) based strategies for preimplantation genetic testing of aneuploidy (PGT-A) improve clinical outcomes after assisted reproductive technology (ART)?

Summary answer

Recent randomised controlled trials (RCTs) suggest that NGS-based PGT-A strategies can improve clinical outcomes for older women. The clinical management of mosaic embryos remains controversial.

What is known already

There are two types of chromosome abnormalities present in embryos, meiotic arising mostly during oogenesis, and mitotic arising after fertilisation. Meiotic aneuploidies are present in all of the embryonic cells and in their vast majority are lethal. Conversely, mitotic abnormalities are present in only part of the embryonic cells with the remaining cells having a different cytogenetic constitution. This phenomenon is known as mosaicism. The sensitivity of NGS meant that mosaic aneuploidy became readily detectable in trophectoderm (TE) samples during PGT-A. The viability and clinical management of mosaic embryos has led to debates and controversies in the reproductive medicine field.

Study design, size, duration

The study involved an assessment of the impact of mosaic chromosome abnormalities to embryonic viability and clinical outcomes after ART cycles using PGT-A via NGS. A large number of embryos generated in IVF clinics in Europe and the USA was examined.

Participants/materials, setting, methods

Embryos were generated by couples referred for PGT-A due to various indications. All embryos were cultured to the blastocyst stage, and underwent a TE biopsy, followed by vitrification. TE samples were shipped to 6 reference PGT laboratories and analysed via the use of the same NGS platform. Mosaic chromosome abnormalities were scored according to validated thresholds set by the reference laboratories. The clinical management of mosaic embryos took place according to published guidelines.

Main results and the role of chance

Comparison of clinical outcomes seen after the transfer of mosaic embryos with those seen after the transfer of euploid embryos led to the following findings:

Mosaic embryos with <40% abnormal cells in the TE sample had an OIR of 50% compared to 27% for mosaics with 40–80% abnormal cells in the TE, and 9% for complex mosaic embryos. Karyotyping of ongoing pregnancies resulting after the transfer of mosaic embryos demonstrated a normal chromosome constitution of the resulting foetuses.

Limitations, reasons for caution

- Cytogenetic classification was based on TE samples removed from blastocysts during PGT-A analysis. As only a fraction of the cells from each embryo are tested, inevitably some mosaic embryos will be incorrectly classified fully euploid or aneuploid. However, this misclassification is expected to have little impact on the results.

Wider implications of the findings

- The transfer of NGS-classified mosaic embryos was associated with poorer clinical outcomes compared to euploid embryos. However, the ongoing pregnancies resulting from mosaic transfers were euploid. NGS’s ability to identify embryos of reduced viability has the potential to improve IVF clinical outcomes.

O-122 ICSI in a box: development of a successful automated sperm injection robot with external supervision and minimal manual intervention

Study question

Is it possible to automate the way sperm is injected in an oocyte and improve ICSI consistency between embryologists?

Summary answer

The developed ICSI robot demonstrated a high degree of consistency and operator skill independence, allowing human supervision and external control, but minimal manual intervention.

What is known already

ICSI is a clinical procedure that is currently performed worldwide in most IVF centers and its use will only increase with more utilization of egg freezing. Since its implementation, the technique has been conducted manually by highly skilled embryologists. However, success rates can vary significantly depending on the experience of the operator. We leverage our experience in robotics, AI algorithms and embryology to develop an automated ICSI robot that requires minimal manual intervention with the aim to standardize the consistency of the procedure and, ultimately, improve overall results maintaining embryologist oversight.

Study design, size, duration

The ICSI robot was developed to have supervised automated control on critical steps of the injection procedure, including injection pipette advancement, zona pellucida and oolemma penetration with piezo-pulses, and pipette removal after injection. Manual intervention is required only for immobilization and capture of spermatozoa with a joystick gamepad and to release the sperm in the ooplasm, without the need for micromanipulation skills. In parallel, piezo-ICSI was performed in a conventional micromanipulation station as a control.

Participants/materials, setting, methods

Hamster and mouse oocytes were collected from superovulated females. For testing the efficiency of the automated system, hamster oocytes were injected with human donor sperm, as historically used in manual ICSI training programs, and survival rates evaluated after overnight culture. Mouse oocytes were injected with mouse sperm heads and subsequently cultured in vitro for five days. Blastocysts obtained were vitrified and embryo transfers are ongoing to evaluate term developmental rates.

Main results and the role of chance

The technical components of the ICSI robot were engineered to integrate AI algorithms, optics, cell microinjectors and mechatronics. AI algorithms were developed to identify the morphological structures of MII oocytes, including the zona pellucida, perivitelline space and polar body, both in the hamster and mouse models. The system detects and analyzes both the pipette and the oocyte and chooses the best area and plane for injection, allowing automated control of the subsequent injection steps. Using the hamster oocyte-human sperm model, a survival rate of 91% (n = 110) was achieved with the robot, which was statistically similar (p = 0.335) to the results obtained in the controls injected manually (96%, n = 28). The average time spent in each injection cycle, which includes scanning of the oocyte and injection pipette, and injection of the sperm into the oocyte, was approximately two minutes per ICSI operation. This time was comparable to the time required by highly experienced operators with manual piezo-injection. In the mouse, 91% (n = 53) of the oocytes injected survived the procedure, of which, 92% developed to two-cells and 87% to the blastocyst stage. No statistical differences were found when compared these efficiencies with manual controls (n = 40, 98%, 97% and 92%, respectively).

Limitations, reasons for caution

The developed ICSI robot has shown highly consistent results, independently of operator skills, both in hamster and mouse oocytes. However, additional validations should be performed to enlarge the sample size of injected oocytes and to evaluate the efficiency of the system in other oocyte species, including translational studies to humans.

Wider implications of the findings

The combination of multidisciplinary teams allows the development of automated processes that can reduce variability in certain IVF procedures, while supervised and assisted by experienced embryologists. It is expected that other laboratory procedures can be automated in the field of assisted reproductive treatments in a near future.

Trial registration number

N/A

Mitochondrial DNA quantification as a tool for embryo viability assessment: retrospective analysis of data from single euploid blastocyst transfers

STUDY QUESTION

Does the amount of mitochondrial DNA (mtDNA) in blastocyst biopsy specimens have the potential to serve as a biomarker of euploid embryo implantation ability, independent of morphology?

SUMMARY ANSWER

The results of this study strongly suggest that elevated mtDNA levels, above a previously defined threshold, are strongly associated with blastocyst implantation failure and represent an independent biomarker of embryo viability.

WHAT IS KNOWN ALREADY

Improved methods of embryo selection are highly desirable in order to increase the efficiency of IVF treatment. At present, even the transfer of chromosomally normal embryos of high morphological grade cannot guarantee that a pregnancy will follow. Recently, it has been proposed that the quantity of mtDNA in embryonic cells may be an indicator of developmental potential, with higher levels of mtDNA associated with reduced implantation. However, thus far reported data sets have been relatively small and in some cases have lacked appropriate validation.

STUDY DESIGN, SIZE, DURATION

This large, blinded, retrospective study involved the analysis of relative mtDNA levels in 1505 euploid blastocysts obtained from 490 couples undergoing preimplantation genetic testing for aneuploidy. Implantation outcomes were compared to mtDNA levels in order to determine the capacity of the method to predict viability and to assess the validity of previously established thresholds.

PARTICIPANTS/MATERIALS, SETTING, METHODS

DNA from blastocyst biopsy samples was amplified and then subjected to aneuploidy analysis using next generation sequencing or array comparative genomic hybridization. Only those embryos classified as chromosomally normal had their mtDNA levels assessed. This analysis was undertaken retrospectively using quantitative real-time PCR, without knowledge of the outcome of embryo transfer. Predictions of implantation failure, based upon mtDNA levels were subsequently compared to the observed clinical results. All cycles involved the transfer of a single embryo.

MAIN RESULTS AND THE ROLE OF CHANCE

Of all blastocysts analyzed, 9.2% (139/1505) contained mtDNA levels above a previously established viability threshold and were therefore predicted to have reduced chances of implantation. To the date of analysis, 282 euploid blastocysts had been transferred with an overall implantation rate of 65.6% (185/282). Of the transferred embryos, 249 contained levels of mtDNA in the normal range, 185 of which produced a pregnancy, giving an implantation rate of 74.3% for euploid embryos with 'normal' quantities of mtDNA. However, 33 of the transferred embryos were determined to have elevated mtDNA quantities. None of these led to a pregnancy. Therefore, the negative predictive value of mtDNA assessment in this cohort was 100% (33/33). The difference between the implantation rates for embryos with normal and elevated mtDNA levels was highly significant (P < 0.0001). The mtDNA thresholds, used for classification of embryos, were unaffected by female age or the clinic in which the IVF was undertaken. The probability of an embryo having elevated levels of mtDNA was not influenced by variation in embryo morphology.

LIMITATIONS, REASONS FOR CAUTION

This study provides strong evidence that mtDNA quantification can serve as a valuable tool to assist the evaluation of blastocyst viability. However, to determine the true extent of any clinical benefits, other types of investigations, such as non-selection studies and randomized controlled trials, will also be necessary.

WIDER IMPLICATIONS OF THE FINDINGS

The results of this study suggest that mtDNA quantity can serve as an independent biomarker for the prediction of euploid blastocyst implantation potential. Prospective studies should now be undertaken to confirm these results. Additionally, investigations into the underlying biological cause(s) of elevated mtDNA levels and an enhanced understanding of how they relate to diminished implantation potential would be invaluable.

STUDY FUNDING/COMPETING INTEREST(S)

This study was supported by funding provided by Reprogenetics. None of the authors have any competing interests.