Challenges facing contemporary preimplantation genetic screening

Oocyte quality and embryo selection strategies: a review for the embryologists, by the embryologists

With the advance of assisted reproduction techniques, and the trend towards blastocyst culture and single embryo transfer, gamete and embryo assessment have gained greater importance in ART treatment. Embryo quality depends mainly on gamete quality and culture conditions. Oocyte maturity identification is necessary in order to plan fertilization timing. Mature oocytes at the metaphase II stage show a higher fertilization rate compared to immature oocytes. Morphology assessment is a critical yet challenging task that may serve as a good prognostic tool for future development and implantation potential if done effectively. Various grading systems have been suggested to assess embryos at pronuclear, cleavage, and blastocyst stages. By identifying the embryo with the highest implantation potential, it is possible to reduce the number of embryos transferred without compromising the chances of a successful pregnancy. Apart from the conventional morphology assessment, there are several invasive or non-invasive methods for embryo selection such as preimplantation genetic testing, morphokinetics, proteomics, metabolomics, oxygen consumption, and measurement of oxidative stress in culture medium. Morphokinetics is a method based on time-lapse technology and continuous monitoring of embryos. In this review, we aim to describe and compare the most effective and widely used methods for gamete and embryo assessment as well as embryo selection.

Preimplantation Genetic Testing for Polygenic Disease Relative Risk Reduction: Evaluation of Genomic Index Performance in 11,883 Adult Sibling Pairs

Preimplantation genetic testing for polygenic disease risk (PGT-P) represents a new tool to aid in embryo selection. Previous studies demonstrated the ability to obtain necessary genotypes in the embryo with accuracy equivalent to in adults. When applied to select adult siblings with known type I diabetes status, a reduction in disease incidence of 45-72% compared to random selection was achieved. This study extends analysis to 11,883 sibling pairs to evaluate clinical utility of embryo selection with PGT-P. Results demonstrate simultaneous relative risk reduction of all diseases tested in parallel, which included diabetes, cancer, and heart disease, and indicate applicability beyond patients with a known family history of disease.

Novel noninvasive embryo selection algorithm combining time-lapse morphokinetics and oxidative status of the spent embryo culture medium

OBJECTIVE

To develop a noninvasive embryo selection algorithm consisting of time-lapse morphokinetics and the oxidative status of the spent embryo culture medium determined using the Thermochemiluminescence (TCL) Analyzer.

DESIGN

Retrospective cohort.

SETTING

Not applicable.

PATIENT(S)

From women participating in the oocyte donation program, data from 505 samples of spent embryo culture media samples from 292 intracytoplasmic sperm injection cycles.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Morphokinetic parameters assessed during incubation in the time-lapse system Embryoscope. Oxidative parameters (H1_sm, H2_sm, and H3_sm) from the spent culture medium on day 5 of incubation measured using the TCL assay; and a combined assessment algorithm, including morphology, morphokinetics, and the embryo's culture medium oxidative status, developed as a tool for embryo selection, based on implantation success and confirmed ongoing pregnancy.

RESULT(S)

The levels of the oxidative parameters H1_sm, H2_sm, and H3_sm on day 5 of incubation were statistically significantly higher in transferred and vitrified embryos compared with discarded embryos and in successfully implanted embryos compared with those that did not result in pregnancy. The assessment algorithm resulted in a hierarchical classification with six embryo quality categories (A to F), associated with implantation rates of between 76.5% and 29.2%.

CONCLUSION(S)

An assessment algorithm combining morphology, morphokinetics and the embryo's culture medium oxidative status may help to improve current embryo selection methods criteria and in vitro fertilization success.

National mosaic embryo transfer practices: a survey

BACKGROUND

The growing use of preimplantation genetic testing with in vitro fertilization has provided clinicians with more information about the genetics of embryos. Embryos, however, sometimes result with a mixed composition of both aneuploid and euploid cells, called mosaic embryos. The interpretation of these results has varied, leading some clinicians to transfer mosaic embryos and some opt not to. In addition, laboratories providing preimplantation genetic testing for aneuploidy have differing thresholds for determining an embryo aneuploid, mosaic, or euploid. Overall practice patterns for mosaic embryo transfer practices in the United States are unknown.

OBJECTIVE(S)

The objectives of the study were to characterize national mosaic embryo transfer practices, including the use of preimplantation genetic testing for aneuploidy, prior history of transferring mosaic embryos, thresholds for determining mosaicism, and willingness to transfer mosaic embryos among assisted reproductive technology clinics in the United States.

STUDY DESIGN

A 14 question online survey assessing current use of preimplantation genetic testing for aneuploidy, thresholds for determining mosaicism, and clinic experience and willingness to transfer mosaic embryos was e-mailed to 405 assisted reproductive technology clinics across the United States. Descriptive statistics and logistic regression were used to analyze survey responses and identify clinical factors associated with reporting having ever transferred a mosaic embryo.

RESULTS

Of the 405 US assisted reproductive technology clinics contacted, 252 (62.2%) completed a survey, including 157 private (62.3%), 55 academic (21.8%), and 40 hybrid (15.9%) clinics. Most clinics (168, 66.7%) reported conducting preimplantation genetic testing for aneuploidy on less than 50% of all in vitro fertilization cycles. The most common type of preimplantation genetic testing for aneuploidy technology used was next-generation sequencing at 88.9%. Ninety-one clinics (36.1%) receive mosaicism data on their preimplantation genetic testing for aneuploidy report; the most common thresholds for determining embryo aneuploidy and euploidy by clinics' primary genetics laboratories were <20% normal (36.3%) and >80% normal (46.2%), respectively. Thirty-nine (42.9%) of the 91 have transferred and 57 (62.6%) would transfer a mosaic embryo. Nearly 40% of clinics were unsure about their thresholds for mosaic transfer and one fourth of clinics reported they had no threshold. Private (odds ratio, 1.0, 95% confidence interval, 0.5-1.8) and hybrid (odds ratio, 0.9, 95% confidence interval, 0.4-2.1) clinics were just as likely as academic clinics to report having transferred a mosaic embryo. Clinics in the northeastern United States were more likely to have transferred a mosaic embryo than clinics in other regions (odds ratio, 1.5, 95% confidence interval, 0.9-2.7). Most clinics (72.6%) report they do not have a unique consent for transfer of mosaic embryos.

CONCLUSION

There is uncertainty and variability in the transfer practices of mosaic embryos and classification of mosaicism among US assisted reproductive technology clinics. These findings provide an opportunity to establish mosaicism thresholds and create standardized guidelines for transferring mosaic embryos.

Preimplantation Genetic Screening with Spent Culture Medium/Blastocoel Fluid for in Vitro Fertilization

Preimplantation genetic screening (PGS) detects chromosomal aneuploidy from DNA extracted from trophectodermal biopsy of the embryos before implantation. Although a controlled study showed no difference in pregnancy rates between this invasive cell biopsy technique and a non-biopsied control group, the potential long-term damage by the current PGS method has not be completely ruled out. We therefore tested a less-invasive protocol which utilizes spent culture medium combining with blastocoel fluid (ECB) to assess chromosomal aneuploidy. We compared the new protocol with the currently employed trophectodermal biopsy method against chromosomal information obtained from the remaining embryo. We found that the new technique generated information about aneuploidy that was not entirely identical to obtained from the biopsied trophectoderm or the remaining embryo. As the origins of the DNA extracted from the three sample types were not the same, the significance and interpretation of each result would have its own meaning. The possible implications derived from the ECB results as well as those from cell biopsy were discussed. The effectiveness of this new approach in selecting the best embryo for uterine implantation awaits further long term evaluation.

Effect of next-generation sequencing in preimplantation genetic testing on live birth ratio

The present study analysed live birth ratios in frozen embryo transfer (FET) cycles where embryo ploidy status was determined with preimplantation genetic testing (PGT) using next-generation sequencing (NGS). PGT was performed on trophectoderm cells biopsied at the blastocyst stage. The present prospective cohort study included 112 women undergoing frozen embryo transfer, with NGS PGT. The control group consisted of 85 patients who underwent the IVF procedure with FET planned for a subsequent cycle. The live birth rate per cycle was higher by ~18.5 percentage points in the investigated compared with control group (42.0% vs 23.5% respectively; P = 0.012). The differences between the study and control groups were also significant for clinical pregnancy (42.0% vs 23.5% respectively; P = 0.012), implantation (41.2% vs 22.2% respectively; P = 0.001) and pregnancy loss rates (9.6% vs 28.6% respectively; P = 0.027). The results show that PGT NGS is a useful method for embryo selection and it may be implemented in routine clinical practice with propitious results.

A randomized and blinded comparison of qPCR and NGS-based detection of aneuploidy in a cell line mixture model of blastocyst biopsy mosaicism

PURPOSE

A subset of preimplantation stage embryos may possess mosaicism of chromosomal constitution, representing a possible limitation to the clinical predictive value of comprehensive chromosome screening (CCS) from a single biopsy. However, contemporary methods of CCS may be capable of predicting mosaicism in the blastocyst by detecting intermediate levels of aneuploidy within a trophectoderm biopsy. This study evaluates the sensitivity and specificity of aneuploidy detection by two CCS platforms using a cell line mixture model of a mosaic trophectoderm biopsy.

METHODS

Four cell lines with known karyotypes were obtained and mixed together at specific ratios of six total cells (0:6, 1:5, 2:4, 3:3, 4:2, 5:1, and 6:0). A female euploid and a male trisomy 18 cell line were used for one set, and a male trisomy 13 and a male trisomy 15 cell line were used for another. Replicates of each mixture were prepared, randomized, and blinded for analysis by one of two CCS platforms (quantitative polymerase chain reaction (qPCR) or VeriSeq next-generation sequencing (NGS)). Sensitivity and specificity of aneuploidy detection at each level of mosaicism was determined and compared between platforms.

RESULTS

With the default settings for each platform, the sensitivity of qPCR and NGS were not statistically different, and 100 % specificity was observed (no false positives) at all levels of mosaicism. However, the use of previously published custom criteria for NGS increased sensitivity but also significantly decreased specificity (33 % false-positive prediction of aneuploidy).

CONCLUSIONS

By demonstrating increased false-positive diagnoses when reducing the stringency of predicting an abnormality, these data illustrate the importance of preclinical evaluation of new testing paradigms before clinical implementation.