. Preimplantation genetic screening and diagnosis
Steven R. Bayer, Michael M. Alper in Boston IVF Handbook of Infertility, 2007
Preimplanation genetic screening (PGS) and diagnosis (PGD) are techniques that provide genetic and chromosomal information about developing embryos through biopsy and analysis of embryonic cellular material. This technology is applicable and helpful to many couples seeking conception through IVF, particularly those with a known risk of transmitting single gene disorders to their offspring or those at risk of generating embryos with structural or numeric chromosomal abnormalities. In couples using PGD, accurate and reliable determination of single gene defects, chromosome structure, and chromosome number in blastomere or polar body biopsies is used to guide embryo selection prior to transfer. For many, this is a far more desirable option than awaiting fetal diagnosis in the first or second trimester of pregnancy via chorionic villus sampling or amniocentesis. While continuing to rapidly expand, PGD has become a routine option for patients to prevent the transmission of known single gene diseases and to enhance the chance of pregnancy and live birth for couples with repeated IVF failure, recurrent pregnancy loss, or advanced maternal age.
Chromosome abnormalities in human embryos
David. K Gardner, Ariel Weissman, Colin M. Howles, Zeev Shoham in Textbook of Assisted Reproductive Techniques, 2005
This chapter is an update to our previous reviews on this subject.1,2 In those reviews we explained that when an in vitro fertilization (IVF) clinic successfully attains a high implantation rate, it can be faced with the problem of excessive multiple pregnancies. Also, many women of advanced maternal age may lose their pregnancies to spontaneous abortions. Therefore, embryo selection becomes of central importance. Here we review the latest methods using numerical chromosome assessment as one of the main criteria for selection in these situations. To study numerical chromosome abnormalities in human preimplantation embryos, certain conditions need to be met. First, individual chromosomes need to be assessed to determine specific aneuploidy rates. Second, all or most blastomeres in some embryos should be analyzed to differentiate mosaicism from other abnormalities. Third, developmentally arrested embryos should also be fully analyzed, and finally, abnormalities should be assessed at different times of development (cleavage, morula, blastocyst stage).
Preimplantation Genetic Testing of Aneuploidies (PGT-A)
Carlos Simón, Carmen Rubio in Handbook of Genetic Diagnostic Technologies in Reproductive Medicine, 2022
Aneuploidy refers to a phenomenon whereby the total number of chromosomes in an individual deviates from the usual 23 pairs (46 chromosomes) and is the primary cause of miscarriage. Preimplantation genetic testing for aneuploidy (PGT-A) is a complementary test to IVF which aims to prevent chromosomal disorders in newborns, reduce miscarriage rates and improve implantation and live birth rates (LBR) by identifying aneuploid embryos that are associated with poor clinical outcomes. PGT-A requires a biopsy sample from an embryo or oocyte to gather sufficient DNA which can be amplified, tested, and analyzed for the presence of chromosomal aberrations. Retrospective studies and randomized controlled trials (RCT) have suggested that PGT-A increases live births, reduces time to pregnancy and miscarriage rate, and is favorable towards implantation rates and ongoing pregnancy. However, evidence is often inconsistent and several publications using fluorescence in situ hybridization (FISH) and blastomere biopsies raised concerns over the clinical significance and application of PGT-A. Despite recent advances in the procedure, including improved biopsy timing, higher throughput comprehensive chromosome screening (CCS) platforms, and optimized cryopreservation protocols, widespread controversy regarding the effectiveness, safety, and benefits of PGT-A remains. Moreover, ethical and financial dilemmas must be considered before proceeding with treatment, including the moral status of an embryo and the psychological and financial burden which may accompany abnormal PGT-A results. Nevertheless, in clinics employing best laboratory practice (including high blastocyst development rates, excellent cryopreservation combined with experienced blastocyst biopsy practitioners), as well as accurate, reproducible, and well-validated tests (e.g., next-generation sequencing (NGS), the positive effects of PGT-A should be considered when counseling IVF patients.
Blastomere multinucleation: Contributing factors and effects on embryo development and clinical outcome
Published in Human Fertility, 2010
Rita De Cássia Savio Figueira, Amanda Souza Setti, Daniela Paes De Almeida Ferreira Braga, Assumpto Iaconelli, Edson Borges
Introduction. The aim of the study was to discover which intracytoplasmic sperm injection (ICSI) cycle parameters could influence the presence of multinucleated blastomeres (MNBs) and how ICSI outcomes are influenced by this event. Material and methods. Embryos derived from normally fertilised oocytes were divided into two groups: embryos that had only mononucleated blastomeres (NBs group n = 2818) and embryos that had at least one multinucleated blastomere (MNB group, n = 404). The effects of ICSI cycle factors on multinucleation were investigated and embryo development was compared between the groups. The cycles were also split into those in which only NB embryos were present (NB cycles, n = 298) and cycles in which MNB embryos were present (MNB cycles, n = 203). ICSI outcomes were compared between the groups. Results. A higher incidence of MNB embryos arose in pituitary blockage with gonadotropin-releasing hormone agonists, male factor infertility and in cycles with higher number of retrieved oocytes. Embryos that had only one affected blastomere showed greater development than embryos with more than one affected blastomere. Finally, the implantation rate decreased when MNB embryos were transferred. Conclusion. Multinucleation events may be affected by aspects of the ICSI cycle and compromise embryo quality and implantation rate.
Laser microbeam-induced DNA damage inhibits cell division in fertilized eggs and early embryos
Published in Cell Cycle, 2013
Zhong-Wei Wang, Xue-Shan Ma, Jun-Yu Ma, Yi-Bo Luo, Fei Lin, Zhen-Bo Wang, Heng-Yu Fan, Heide Schatten, Qing-Yuan Sun
DNA double-strand breaks are caused by both intracellular physiological processes and environmental stress. In this study, we used laser microbeam cut (abbreviated microcut or cut), which allows specific DNA damage in the pronucleus of a fertilized egg and in individual blastomere(s) of an early embryo, to investigate the response of early embryos to DNA double-strand breaks. Line type γH2AX foci were detected in the cut region, while Chk2 phosphorylation staining was observed in the whole nuclear region of the cut pronuclei or blastomeres. Zygotes with cut male or female pronucleus showed poor developmental capability: the percentage of cleavage embryos was significantly decreased, and the embryos failed to complete further development to blastocysts. The cut blastomeres in 2-cell, 4-cell, and 8-cell embryos ceased cleavage, and they failed to incorporate into compacted morulae, but instead underwent apoptosis and cell death at the blastocyst stage; the uncut part of embryos could develop to blastocysts, with a reduced percentage or decreased cell number. When both blastomeres of the 2-cell embryos were cut by laser microbeam, cell death occurred 24 h earlier, suggesting important functions of the uncut blastomere in delaying cell death of the cut blastomere. Taken together, we conclude that microbeam-induced DNA damage in early embryos causes compromised development, and that embryos may have their own mechanisms to exclude DNA-damaged blastomeres from participating in further development.
Does sperm DNA fragmentation affect the developmental potential and the incidence of apoptosis following blastomere biopsy?
Published in Systems Biology in Reproductive Medicine, 2016
Tahereh Haghpanah, Mohammad Salehi, Marefat Ghaffari Novin, Reza Masteri Farahani, Fatemeh Fadaei-Fathabadi, Maryam Dehghani-Mohammadabadi, Hadi Azimi
Common methods employed in assisted reproduction technology (ART) include intracytoplasmic sperm injection (ICSI) with an unspecified level of sperm DNA fragmentation (SDF) and preimplantation genetic diagnosis (PGD). The aim of this study was to investigate the impact of SDF on human preimplantation embryo development and the incidence of apoptosis following a single blastomere biopsy. Using sperm chromatin dispersion (SCD) to assess SDF, a total of 20 processed semen samples were categorized into two groups; group I: SDF ≤30% and group II: SDF >30%. After ICSI, fertilization, cleavage, and embryo quality score were assessed. A single blastomere was biopsied from day 3 embryos and development was monitored on day 4. The frequency of apoptosis in biopsied embryos was assayed by TUNEL and the level of BCL-2, BAX, hsa-mir-15a, and hsa-mir-16-1 were assessed by quantitative real-time polymerase chain reaction (qRT-PCR). SCD was found to be negatively correlated with sperm motility and normal form spermatozoa (p < 0.05). The rate of fertilization, cleavage, and embryo quality score were not significantly different between the two groups (all p > 0.05). SDF >30% had no negative effect on potential development and did not increase the proportion of apoptotic cells and the level of apoptosis-related genes and microRNAs (miRNAs) in group II vs. group I (p > 0.05). It appears that at the levels assessed paternal genome damage had little if any negative effect on preimplantaton embryo development and apoptosis following single blastomere biopsy. This may reflect the selection of morphologically normal sperm for ICSI and the repair capacity of the oocyte.
Related Knowledge Centers
- Zygote
- Blastocyst
- Cell