Use of comprehensive chromosomal screening for embryo assessment: microarrays and CGH

One of the most important factors influencing embryo viability is chromosome imbalance (aneuploidy). Embryos derived from aneuploid gametes have little potential for forming a viable pregnancy, but cannot be distinguished from normal embryos using standard morphological evaluation. For more than a decade, preimplantation genetic screening (PGS) has been used to assist in the identification of aneuploid embryos. However, current strategies, based upon cell biopsy followed by fluorescent in situhybridization, allow less than half of the chromosomes to be screened. In this review, we discuss methods that overcome the limitations of earlier PGS strategies and provide screening of the entire chromosome complement in oocytes and embryos. In recent months, there has been a rapid growth in the number of PGS cycles utilizing one such method, comparative genomic hybridization (CGH). Data from IVF cycles utilizing CGH must be considered preliminary, but appear to indicate a dramatic increase in embryo implantation following comprehensive chromosomal screening. It is expected that methods based upon microarrays will yield similar clinical results and may be sufficiently rapid to permit comprehensive screening without the need for embryo cryopreservation. Some microarray platforms also offer the advantage of embryo fingerprinting and the potential for combined aneuploidy and single gene disorder diagnosis. However, more data concerning accuracy and further reductions in the price of tests will be necessary before microarrays can be widely applied

Detailed investigation into the cytogenetic constitution and pregnancy outcome of replacing mosaic blastocysts detected with the use of high-resolution next-generation sequencing

Objective: To determine the pregnancy outcome potential of mosaic embryos, detected by means of preimplantation genetic screening (PGS) with the use of next-generation sequencing (NGS). Design: Retrospective study. Setting: Genetics laboratories. Patient(s): PGS cycles during which either mosaic or euploid embryos were replaced. Intervention(s): Blastocysts were biopsied and processed with the use of NGS, followed by frozen embryo transfer. Trophectoderm (TE) biopsies were classified as mosaic if they had 20%–80% abnormal cells. Main Outcome Measure(s): Implantation, miscarriage rates, and ongoing implantation rates (OIRs) were compared between euploid and types of mosaic blastocysts. Result(s): Complex mosaic embryos had a significantly lower OIR (10%) than aneuploidy mosaic (50%), double aneuploidy mosaic (45%), and segmental mosaic (41%). There was a tendency for mosaics with 40%–80% abnormal cells to have a lower OIR than those with 40% abnormal cells and those with multiple mosaic abnormalities (chaotic mosaics) are likely to have lower OIRs and should be given low transfer priority

The detection of chromosomal abnormalities in human oocytes and preimplantation embryos by molecular cytogenetic analysis

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Patient information.

<p>Bla: Blastomere; PB: polar body; TE: trophectoderm cells; aCGH: Microarray-CGH; Met-CGH: Metaphase CGH. Note: Some patients underwent more than one cycle of PGD and may have had analysis conducted at different stages in subsequent cycles.</p

Number of embryos from each cycle and the number of chromosomes assessed along with abnormalities detected.

<p>Rec: reciprocal translocation; Rob: Robertsonian translocation; Inv: Inversion; Bla: Blastomere; PB: polar body; TE: trophectoderm cells.</p>*<p>Chromosomes involved in the rearrangement were not assessed;</p>**<p>Abnormalities affecting chromosomes involved in the rearrangement were excluded. Case 12 was the only one in which two rearrangements were present. This case was excluded from the statistical analysis.</p

Malsegregation events detected in non-rearranged chromosomes in patient and control samples.

<p>Malsegregation events detected in non-rearranged chromosomes in patient and control samples.</p