Theory and practice of preimplantation genetic screening (PGS)

Research progress and challenges of preimplantation genetic testing for polygenic diseases

Preimplantation genetic testing is an important part in assisted reproductive technology, which can block the intergenerational inheritance of single gene or chromosomal diseases. Preimplantation genetic testing for polygenic disease risk (PGT-P) is the latest development in the field. It is known that polygenic diseases usually have the characteristics of high incidence, late onset, affecting the quality of life and mental health of patients. On the basis of the development of artificial intelligence and genetic detection technology, PGT-P can analyze genetic material, calculate polygenic risk score turning into incidence probability. Embryos with relatively low incidence probability can be screened for transfer, so as to reduce the possibility of offspring suffering from the disease in the future, which has significant clinical and social significance. At present, PGT-P has been applied clinically and made phased progress at home and abroad. At the same time, as a developing technology, PGT-P still has some technical defects, unstable results, environmental influences and racial differences cannot be ruled out. From the perspective of ethics, if the screening indications are not strictly regulated, it is likely to cause new social problems. In this paper, we review the technical composition and recent progress of PGT-P, and put forward the prospect of its future development, especially how to establish a complete and suitable screening model for Chinese population.

Systematic review of subsequent pregnancy outcomes in couples with parental abnormal chromosomal karyotypes and recurrent pregnancy loss

OBJECTIVE

To evaluate the current evidence of pregnancy outcomes among couples with recurrent pregnancy loss (RPL) with abnormal karyotypes vs. those with normal karyotypes and among couples with RPL and abnormal karyotypes after receiving expectant management vs. preimplantation genetic diagnosis (PGD).

DESIGN

Systematic review and meta-analysis.

SETTING

Academic medical centers.

PATIENT(S)

Pregnancy outcomes in 6,301 couples with RPL who conceived without medical intervention in 11 studies were analyzed. However, only 2 studies addressed the outcomes of couples with RPL and abnormal karyotypes after expectant management (75 cases) vs. PGD (50 cases).

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

The pregnancy outcomes in couples with RPL with abnormal and normal karyotypes across included studies were evaluated.

RESULT(S)

Compared with those with a normal karyotype, a significantly lower first pregnancy live birth rate (LBR) was found in couples with RPL with abnormal karyotypes (58.5% vs. 71.9%; odds ratio [OR], 0.55; 95% confidence interval [CI], 0.46-0.65; I² =27%). A markedly decreased first pregnancy LBR was found in couples with a translocation (52.9% vs. 72.4%; OR, 0.44; 95% CI, 0.31-0.61; I² =33%) but not in couples with an inversion. However, the differences in accumulated LBR (81.4% vs. 74.8%; OR, 0.96; 95% CI, 0.90-1.03; I² = 0) were nonsignificant, whereas the miscarriage rate was distinctly higher in couples with RPL and abnormal karyotypes (53.0% vs. 34.7%; OR, 2.21; 95% CI, 1.69-2.89; I² = 0). Compared with those who chose expectant management, differences in accumulated LBR were nonsignificant (60% vs. 68%; OR, 0.55; 95% CI, 0.11-2.62; I² =71%), whereas the miscarriage rate (24% vs. 65.3%; OR, 0.15; 95% CI, 0.04-0.51; I² = 45) was markedly low in couples with RPL and abnormal karyotypes who chose PGD.

CONCLUSION(S)

Couples with RPL and abnormal karyotypes had a higher miscarriage rate than couples with normal karyotypes but achieved a noninferior accumulated LBR through multiple conception attempts. In couples with RPL and abnormal karyotypes, PGD treatment did not increase the accumulated LBR but markedly reduced miscarriage rate compared with expectant management.

Implementation and Evaluation of Preimplantation Genetic Testing at Vilnius University Hospital Santaros Klinikos

Background and Objectives

The most effective treatment of infertility is in vitro fertilization (IVF). IVF with Preimplantation Genetic Testing (PGT) allows to identify embryos with a genetic abnormality associated with a specific medical disorder and to select the most optimal embryos for the transfer. PGT is divided into structural rearrangement testing (PGT-SR), monogenetic disorder testing (PGT-M), and aneuploidy testing (PGT-A). This study mostly analyzes PGT-SR, also describes a few cases of PGT-M. The aim of this study was to implement PGT procedure at Vilnius University Hospital Santaros Klinikos (VUHSK) Santaros Fertility Centre (SFC) and to perform retrospective analysis of PGT procedures after the implementation.

Materials and Methods

A single-center retrospective analysis was carried out. The study population included infertile couples who underwent PGT at SFC, VUHSK from January 01st, 2017 to December 31st, 2020. Ion PGM platform (Life Technologies, USA) and Ion ReproSeq PGS View Kit (Life Technologies, USA) were used for the whole genome amplification. Results were assessed using descriptive statistics.

Results

PGT was successfully implemented in VUHSK in 2017. During the analyzed time period, thirty-four PGT procedures were performed for 26 couples. Two procedures were performed in 2017, 7 procedures - in 2018, 13 - in 2019, and 12 - in 2020. In comparison with all IVF procedures, 2.5% procedures were IVF with PGT, a highest percentage was in 2020 (3.8% of all procedures). The main indication for PGT was balanced chromosomal rearrangements (in 85.3% cases). In all 34 cases 515 oocytes were aspirated in total, 309 oocytes were fertilized, oocytes fertilization rate exceeded 60%. A normal diploid karyotype was found in 46 (16.8%) biopsied embryos. Out of all PGT procedures, 9 (26.5%) resulted in a clinical pregnancy. Six (66.7%) pregnancies were confirmed in 2019, and 3 (33.3%) - in 2020. Three (33.3%) pregnancies resulted in spontaneous abortion, 6 (66.7%) - in delivery.

Conclusions

The implementation of PGT in VUHSK was successful. The most common indication for PGT was a reciprocal translocation. Oocytes fertilization rate exceeded 60%, a normal karyotype was found less than in one-fifth of biopsied embryos. A highest clinical pregnancy rate was achieved in 2019 when almost half of women conceived, which is probably related to the experience gained by the multidisciplinary team. This is the first study analyzing IVF with PGT in Lithuania, however, the results should be interpreted with caution due to a low number of total procedures performed.

[Systematic karyotyping before ICSI: A necessary procedure? Analysis of case studies in the Nancy University Hospital Fertility Centre]

INTRODUCTION

A constitutional karyotype is often assayed for the couple before ICSI management. The objective of this study was to assess the prevalence of chromosomal abnormality in an infertile population, the impact on the care of couples and its cost.

METHODS

A single-center retrospective study was carried out at the Fertility Center of the University Hospital of Nancy, including all infertile couples who underwent a karyotype analysis from June 2009 to December 2016.

RESULTS

1252 couples were included. 7.9% had at least one abnormal karyotype. A change in care affected 22% of these couples, i.e. 1.7% of the total population. 9% of couples with karyotype abnormality underwent PGD. In the male population, the percentage of abnormal spermograms is significantly higher in the group with karyotype abnormality compared to the control group (85.7% vs. 46.5%, P<0.001).

DISCUSSION

The constitutional karyotype, due to its high economic and human cost, and limited interest, is a screening method for chromosomal abnormalities that has no place systematically before performing IVF. The future lies in the restriction of the indications for prescribing the karyotype as well as in the realization of PGS in targeted situations.

Comparison of live birth rates after IVF-embryo transfer with and without preimplantation genetic testing for aneuploidies

RESEARCH QUESTION

Does the use of preimplantation genetic testing for aneuploidies (PGT-A) result in higher live birth rates when compared with both fresh and frozen embryo transfers (FET) not utilizing PGT-A?

DESIGN

Retrospective cohort study at a single tertiary centre using inverse probability of treatment weighting (IPTW) to adjust for differences in baseline characteristics between groups.

RESULTS

A total of 107 FET using PGT-A from 74 patients, along with 321 fresh and 286 FET not using PGT-A from 381 patients met the inclusion criteria for this study. In the IPTW-adjusted analysis of transfer-level data, PGT-A transfers resulted in a significantly higher live birth rate when compared with both non-PGT-A fresh (49.5% versus 38.6%, P = 0.036) and FET (50.6% versus 35.8%, P = 0.016). When data were analysed per retrieval level, the live birth rate was similar and acceptably high with or without PGT-A (63.7% versus 52.3%, P = 0.09).

CONCLUSION

When comparing PGT-A to non-PGT-A fresh and FET, PGT-A embryo transfers have a significantly higher live birth rate. However, this difference did not persist at a per-retrieval level. Further investigation is needed to understand in what scenarios PGT-A has clinical significance and whether differences in the number of available embryos for transfer negates the benefit of PGT-A.

Comparison of preimplantation genetic testing for aneuploidy versus intracytoplasmic sperm injection in severe male infertility

The retrospective cohort study was conducted to evaluate the effectiveness of preimplantation genetic testing for aneuploidy (PGT-A) for severe male factor (SMF) infertility on pregnancy outcomes in comparison with intracytoplasmic sperm injection (ICSI). A total of 206 couples with SMF were included in the study, among which, 102 couples underwent ICSI with next-generation sequencing (NGS)-based PGT-A (the PGT-A group), while 104 underwent ICSI only (the control group). Results showed while no differences were noted in clinical pregnancy rate (CPR) (66.7% versus. 69.9%, p = .64) and ongoing pregnancy rate (OPR) (62.2% versus. 54.7%, p = .29) per transfer between groups, early miscarriage rate (EMR) per transfer was significantly lower (6.7% versus. 21.6%, p = .02) in the PGT-A group. Cumulative OPR per patient remained similar between groups (54.9% versus. 55.8%, p = .90). Results of multivariable logistic regression also demonstrated the use of PGT-A was significantly associated with lower EMR (adjusted OR 0.17, 95%CI 0.05-0.55) in SMF, while it was not related to cumulative OPR. In conclusion, our results showed that NGS-based PGT-A can improve pregnancy outcomes for couples with SMF by significantly decreasing EMR without compromising cumulative OPR, indicating that NGS-based PGT-A could be offered as an appropriate approach for couples with SMF.

A systematic review exploring the patient decision-making factors and attitudes towards pre-implantation genetic testing for aneuploidy and gender selection

INTRODUCTION

Pre-implantation genetic testing for aneuploidy (PGT-A) is in high demand worldwide, with ongoing debate among medical societies as to which patient groups it should be offered. The psychological aspects for patients regarding its use, lag behind the genomic technological advances, leaving couples with limited decision-making support. The development of this technology also leads to the possibility for its utilization in gender selection. Despite the controversy surrounding these issues, very few studies have investigated the psychological aspects of patients using PGT-A.

MATERIAL AND METHODS

This systematic review provides an up-to-date analysis of the psychosocial aspects surrounding PGT for aneuploidy and sex selection, as well as decision-making factors. A systematic search of English peer-reviewed journals of three computerized databases were undertaken following PRISMA guidelines. The qualitative data were extracted using thematic analysis. PROSPERO Registration number: CRD42019126439.

RESULTS

The main outcome measures were patients' motivations, decision-making factors, attitudes and experiences surrounding the use of PGT for aneuploidy and sex selection. Ten studies were included, four for PGT-A and six for sex selection. Attitudes towards PGT-A were positive, with the main motivating factors being decreasing miscarriage rate, reducing the risk of termination of pregnancy and reducing the time to pregnancy. Consistently raised concerns regarding PGT-A were the financial burden and moral beliefs. The vast majority of patients felt sufficiently knowledgeable to make the decision; however, studies did reveal that a minority mis-interpreted certain potential benefits of PGT-A. Studies investigating PGT for sex selection predominantly reported the main motivation was to achieve gender balance within the family dynamic, with most studies finding no difference between couples using PGT for gender selection to have male or female offspring.

CONCLUSIONS

Although this systematic review was limited by the small number of studies investigating this topic, a significant minority of patients appeared to misunderstand certain benefits and limitations of PGT-A. Fertility clinics must ensure they provide adequate counseling to all patients using PGT-A. With the use of PGT-A on the rise globally, there is a need to develop decision support tools for couples who have an increasing number of genetic testing options becoming available to them.

Preimplantation Genetic Testing: Where We Are Today

Background: Preimplantation genetic testing (PGT) is widely used today in in-vitro fertilization (IVF) centers over the world for selecting euploid embryos for transfer and to improve clinical outcomes in terms of embryo implantation, clinical pregnancy, and live birth rates. Methods: We report the current knowledge concerning these procedures and the results from different clinical indications in which PGT is commonly applied. Results: This paper illustrates different molecular techniques used for this purpose and the clinical significance of the different oocyte and embryo stage (polar bodies, cleavage embryo, and blastocyst) at which it is possible to perform sampling biopsies for PGT. Finally, genetic origin and clinical significance of embryo mosaicism are illustrated. Conclusions: The preimplantation genetic testing is a valid technique to evaluated embryo euploidy and mosaicism before transfer.