Improved detection of aneuploid blastocysts using a new 12-chromosome FISH test

The Effect of Teratozoospermia on Sex Chromosomes in Human Embryos

Purpose

The aim of this study is to evaluate the effect of abnormal semen morphology on the frequency of sex chromosomal abnormalities in embryos obtained by ICSI, which represents the first to be studied in Egyptian population.

Methods

Forty-two couples suffering from male infertility due to teratozoospermia were divided into two groups: patients with severe and moderate teratozoospermia (group A and B, respectively). All involved couples were subjected to careful history taking and had a normal clinical examination and karyotype. Females were subjected to hormonal assays, pelvic ultrasound, hysterosalpingography and yielded normal results, while male partners were subjected to computerized semen analysis. Preimplantation genetic diagnosis was performed for all suitably developed embryos including embryo biopsy, fixation of biopsied cells and fluorescent in situ hybridization (FISH) analysis.

Results

Couples included in the two groups were found to be homogenous in terms of age of both partners and duration of infertility. Interpretation of FISH results was performed by evaluation of embryos’ chromosomal constitution as regards abnormalities in chromosomes X, Y and 18. Twenty-seven embryos (48.2%) were found chromosomally abnormal in group A, while only 14 embryos (25.0%) were found chromosomally abnormal in group B. Aneuploidies involved only sex chromosomes were tripled in group A embryos when compared to their frequency in group B embryos (26.8% and 8.3%, respectively) with statistically significant difference between the two groups (p=0.002). Monosomies were the most common type of aneuploidy and were significantly higher in group A (14.3%) when compared to group B (3.6%) (p=0.047). Embryos with mosaic abnormalities were more common in group A (12.5%) when compared to group B (3.6%), however not statistically significantly different (p= 0.162). A significant difference between the two studied groups as regards the total number of potentially viable chromosomal abnormalities detected and the potentially viable sex chromosomal aneuploidies detected (p<0.001 and p=0.002), respectively.

Conclusion

The cases with severe teratozoospermia undergoing ICSI treatment can display a higher rate of sex chromosome aneuploidies in their embryos (threefold) than cases with moderate teratozoospermia.

Preimplantation Genetic Testing for Chromosomal Abnormalities: Aneuploidy, Mosaicism, and Structural Rearrangements

There is a high incidence of chromosomal abnormalities in early human embryos, whether they are generated by natural conception or by assisted reproductive technologies (ART). Cells with chromosomal copy number deviations or chromosome structural rearrangements can compromise the viability of embryos; much of the naturally low human fecundity as well as low success rates of ART can be ascribed to these cytogenetic defects. Chromosomal anomalies are also responsible for a large proportion of miscarriages and congenital disorders. There is therefore tremendous value in methods that identify embryos containing chromosomal abnormalities before intrauterine transfer to a patient being treated for infertility—the goal being the exclusion of affected embryos in order to improve clinical outcomes. This is the rationale behind preimplantation genetic testing for aneuploidy (PGT-A) and structural rearrangements (-SR). Contemporary methods are capable of much more than detecting whole chromosome abnormalities (e.g., monosomy/trisomy). Technical enhancements and increased resolution and sensitivity permit the identification of chromosomal mosaicism (embryos containing a mix of normal and abnormal cells), as well as the detection of sub-chromosomal abnormalities such as segmental deletions and duplications. Earlier approaches to screening for chromosomal abnormalities yielded a binary result of normal versus abnormal, but the new refinements in the system call for new categories, each with specific clinical outcomes and nuances for clinical management. This review intends to give an overview of PGT-A and -SR, emphasizing recent advances and areas of active development.

Advanced paternal age does not affect embryo aneuploidy following blastocyst biopsy in egg donor cycles

PURPOSE

To study the impact of advanced paternal age on embryo aneuploidy.

METHODS

This is a multicenter international retrospective case series of couples undergoing assisted reproduction via in vitro fertilization using donor eggs to control for maternal factors and preimplantation genetic testing for aneuploidy via next-generation sequencing at Igenomix reproductive testing centers. The main outcome measure was the prevalence of embryo aneuploidy in egg donor cycles. Semen analysis data was retrieved for a small subset of the male patients.

RESULTS

Data from 1202 IVF/ICSI egg donor cycles using ejaculated sperm (total 6934 embryos) evaluated using PGT-A between January 2016 and April 2018 in a global population across all Igenomix centers were included. No significant association was identified between advancing paternal age and the prevalence of embryo aneuploidy overall and when analyzing for each chromosome. There was also no significant association between advancing paternal age and specific aneuploid conditions (monosomy, trisomy, partial deletion/duplication) for all chromosomes in the genome.

CONCLUSIONS

This is the largest study of its kind in an international patient population to evaluate the impact of advancing paternal age on embryo aneuploidy. We conclude there is no specific effect of paternal age on the prevalence of embryo aneuploidy in the context of embryo biopsies from egg donor cycles.

Chromosome screening using culture medium of embryos fertilised in vitro: a pilot clinical study

BACKGROUND

Previous studies from this as well as other research groups suggested that non-invasive chromosome screening (NICS) with embryo culture medium can be used to identify chromosomal ploidy and chromosomal abnormalities. We here report a series of clinical cases utilizing the technology.

METHODS

A total of 45 couples underwent in vitro fertilisation during a period between February 2016 and February 2017. Karyotyping revealed normal chromosomes in both partners in 23 couples, and chromosomal rearrangements in at least one partner in 22 couples. Intracytoplasmic sperm injection (ICSI) was used for fertilization. NICS was carried out using embryo culture medium at the blastocyst stage via multiple annealing and looping-based amplification cycles, whole-genome amplification and next-generation sequencing.

RESULTS

A total of 413 embryos were obtained; 170 blastocysts were subjected to NICS. The screening showed euploidy in 79 embryos, aneuploidy in 52 embryos, and mosaic ploidy for 33 embryos. The rate of euploidy was comparable in couples with normal karyotype (50.7%; 38/75) vs. chromosomal rearrangement (43.2%; 41/95). A total of 52 euploid embryos (50 oocyte retrieval cycles) were transferred in 43 women. Biochemical pregnancy rate was 72.0% (36/50). Clinical pregnancy rate was 58.0% (29/50). The rate of spontaneous miscarriage was 3/29 (none with chromosomal aneuploidy). A total of 27 healthy babies were delivered.

CONCLUSIONS

NICS could identify embryo chromosomal abnormalities in couples either with or without chromosomal rearrangement, with satisfying clinical outcomes.

Preimplantation genetic diagnosis in early pregnancy loss✰

Miscarriage is a frequent outcome seen in obstetrics with 1 in 5 pregnancies ending in an early pregnancy loss. Aneuploidy is the most significant single factor affecting early pregnancy failure and miscarriage. The risk of aneuploidy increases significantly with increasing maternal age. There has been tremendous advancement in technology that has made preimplantation genetic testing for aneuploidy reliable and accessible. For women in their mid-to-late 30s there is great utility in the use of PGT-A to facilitate single embryo transfer, reduce the risk of clinical miscarriage and ongoing aneuploidy gestations. The current data supports use of preimplantation genetic testing for aneuploidy and single embryo transfer for this population of women. At this time, more prospective data is needed to determine the effect of preimplantation genetic testing for aneuploidy on rates of miscarriage in the recurrent pregnancy loss population.

Chromosomal analysis in IVF: just how useful is it?

Designed to minimize chances of genetically abnormal embryos, preimplantation genetic diagnosis (PGD) involves in vitro fertilization (IVF), embryo biopsy, diagnosis and selective embryo transfer. Preimplantation genetic testing for aneuploidy (PGT-A) aims to avoid miscarriage and live born trisomic offspring and to improve IVF success. Diagnostic approaches include fluorescence in situ hybridization (FISH) and more contemporary comprehensive chromosome screening (CCS) including array comparative genomic hybridization (aCGH), quantitative polymerase chain reaction (PCR), next-generation sequencing (NGS) and karyomapping. NGS has an improved dynamic range, and karyomapping can detect chromosomal and monogenic disorders simultaneously. Mosaicism (commonplace in human embryos) can arise by several mechanisms; those arising initially meiotically (but with a subsequent post-zygotic 'trisomy rescue' event) usually lead to adverse outcomes, whereas the extent to which mosaics that are initially chromosomally normal (but then arise purely post-zygotically) can lead to unaffected live births is uncertain. Polar body (PB) biopsy is the least common sampling method, having drawbacks including cost and inability to detect any paternal contribution. Historically, cleavage-stage (blastomere) biopsy has been the most popular; however, higher abnormality levels, mosaicism and potential for embryo damage have led to it being superseded by blastocyst (trophectoderm - TE) biopsy, which provides more cells for analysis. Improved biopsy, diagnosis and freeze-all strategies collectively have the potential to revolutionize PGT-A, and there is increasing evidence of their combined efficacy. Nonetheless, PGT-A continues to attract criticism, prompting questions of when we consider the evidence base sufficient to justify routine PGT-A? Basic biological research is essential to address unanswered questions concerning the chromosome complement of human embryos, and we thus entreat companies, governments and charities to fund more. This will benefit both IVF patients and prospective parents at risk of aneuploid offspring following natural conception. The aim of this review is to appraise the 'state of the art' in terms of PGT-A, including the controversial areas, and to suggest a practical 'way forward' in terms of future diagnosis and applied research.

Clinical reassessment of human embryo ploidy status between cleavage and blastocyst stage by Next Generation Sequencing

One of the most important limitations of genetic testing in preimplantation embryos is embryonic mosaicism, especially when performed on D3 with only a single blastomere evaluated. Previous publications, using Array-Comparative Genomic Hybridization (a-CGH) to compare day 3 (D3) biopsies versus trophectoderm biopsies for the analysis of aneuploid embryos, showed similar high concordance rates per embryo diagnosis for D3 biopsies and trophectoderm biopsies. Next generation sequencing (NGS) was introduced lately as a new technique for preimplantation genetic testing for aneuploidies (PGT-A). Using this technique, this retrospective descriptive study evaluated the degree of the concordance of the diagnosis between preimplantation human cleavage stage (D3) and blastocyst stage (D5) embryos. Double biopsies on D3 and D5 were performed on 118 embryos, reaching blastocyst stage on D5 and had not been selected for transfer. As the fertilization law of the United Arab Emirates does not allow embryo freezing, also surplus euploid embryos after D 3 biopsy were included. Analysis of the NGS results from D3 and D5 embryo biopsies showed a total concordance rate per embryo diagnosis of 85.6% for euploid and aneuploid embryos. The concordance rates per embryo chromosomal pattern for embryo diagnosed as aneuploid at both biopsy stages was 82.2%. However, the status regarding the affected chromosomes was not identical on D3 and D5. Hence, the total concordance rate between D3 biopsy and D5 biopsy was limited to 67.8%. This current study clearly demonstrated that the concordance rates between D3 and D5 biopsies in aneuploid and euploid embryos are lower than previously reported.

Number of biopsied trophectoderm cells is likely to affect the implantation potential of blastocysts with poor trophectoderm quality

OBJECTIVE

To evaluate whether the developmental potential of the blastocyst is affected by the number of trophectoderm (TE) cells biopsied in preimplantation genetic diagnosis (PGD) cycles.

DESIGN

Retrospective study.

SETTING

University-affiliated center.

PATIENT(S)

Women underwent PGD cycles of blastocyst biopsy and fluorescence in situ hybridization analysis.

INTERVENTION(S)

Not applicable.

MAIN OUTCOME MEASURE(S)

Biopsied TE cell number of blastocysts, survival, and implantation rates.

RESULT(S)

The biopsied TE cell number was affected by the TE quality and experience of different embryologists. The diagnostic efficiency increased when from one to five cells were biopsied (86.7%, 91.7%%, 96.0%, 96.8%, to 98.7%) and was maximized when more than six cells were biopsied. To compare the clinical efficiencies, blastocysts were divided into four groups according to biopsied TE cell number: 1-5, 6-10, 11-15, and 16-41. For the blastocysts with grade A TE score, no significant difference was observed in the survival and implantation rates among the four groups. For the blastocysts with grades B and C TE scores, the survival rates showed no significant differences among the four groups, but a significant decreasing trend in implantation rates was observed with increasing biopsied TE cell number.

CONCLUSION(S)

The implantation potential is negatively affected by the biopsied TE cell number in blastocysts with poor TE morphological score.

Impact of blastocyst biopsy and comprehensive chromosome screening technology on preimplantation genetic screening: a systematic review of randomized controlled trials

Embryonic aneuploidy is highly prevalent in IVF cycles and contributes to decreased implantation rates, IVF cycle failure and early pregnancy loss. Preimplantation genetic screening (PGS) selects the most competent (euploid) embryos for transfer, and has been proposed to improve IVF outcomes. Use of PGS with fluorescence-in-situ hybridization technology after day 3 embryo biopsy (PGS-v1) significantly lowers live birth rates and is not recommended for use. Comprehensive chromosome screening technology, which assesses the whole chromosome complement, can be achieved using different genetic platforms. Whether PGS using comprehensive chromosome screening after blastocyst biopsy (PGS-v2) improves IVF outcomes remains to be determined. A systematic review of randomized controlled trials was conducted on PGS-v2. Three trials met full inclusion criteria, comparing PGS-v2 and routine IVF care. PGS-v2 is associated with higher clinical implantation rates, and higher ongoing pregnancy rates when the same number of embryos is transferred in both PGS and control groups. Additionally, PGS-v2 improves embryo selection in eSET practice, maintaining the same ongoing pregnancy rates between PGS and control groups, while sharply decreasing multiple pregnancy rates. These results stem from good-prognosis patients undergoing IVF. Whether these findings can be extrapolated to poor-prognosis patients with decreased ovarian reserve remains to be determined.

Reliable single cell array CGH for clinical samples

Background

Disseminated cancer cells (DCCs) and circulating tumor cells (CTCs) are extremely rare, but comprise the precursors cells of distant metastases or therapy resistant cells. The detailed molecular analysis of these cells may help to identify key events of cancer cell dissemination, metastatic colony formation and systemic therapy escape.

Methodology/Principal Findings

Using the Ampli1™ whole genome amplification (WGA) technology and high-resolution oligonucleotide aCGH microarrays we optimized conditions for the analysis of structural copy number changes. The protocol presented here enables reliable detection of numerical genomic alterations as small as 0.1 Mb in a single cell. Analysis of single cells from well-characterized cell lines and single normal cells confirmed the stringent quantitative nature of the amplification and hybridization protocol. Importantly, fixation and staining procedures used to detect DCCs showed no significant impact on the outcome of the analysis, proving the clinical usability of our method. In a proof-of-principle study we tracked the chromosomal changes of single DCCs over a full course of high-dose chemotherapy treatment by isolating and analyzing DCCs of an individual breast cancer patient at four different time points.

Conclusions/Significance

The protocol enables detailed genome analysis of DCCs and thereby assessment of the clonal evolution during the natural course of the disease and under selection pressures. The results from an exemplary patient provide evidence that DCCs surviving selective therapeutic conditions may be recruited from a pool of genomically less advanced cells, which display a stable subset of specific genomic alterations.

Preimplantation genetic diagnosis for aneuploidy and translocations using array comparative genomic hybridization

At least 50% of human embryos are abnormal, and that increases to 80% in women 40 years or older. These abnormalities result in low implantation rates in embryos transferred during in vitro fertilization procedures, from 30% in women <35 years to 6% in women 40 years or older. Thus selecting normal embryos for transfer should improve pregnancy results. The genetic analysis of embryos is called Preimplantation Genetic Diagnosis (PGD) and for chromosome analysis it was first performed using FISH with up to 12 probes analyzed simultaneously on single cells. However, suboptimal utilization of the technique and the complexity of fixing single cells produced conflicting results. PGD has been invigorated by the introduction of microarray testing which allows for the analysis of all 24 chromosome types in one test, without the need of cell fixation, and with staggering redundancy, making the test much more robust and reliable. Recent data published and presented at scientific meetings has been suggestive of increased implantation rates and pregnancy rates following microarray testing, improvements in outcome that have been predicted for quite some time. By using markers that cover most of the genome, not only aneuploidy can be detected in single cells but also translocations. Our validation results indicate that array CGH has a 6Mb resolution in single cells, and thus the majority of translocations can be analyzed since this is also the limit of karyotyping. Even for translocations with smaller exchanged fragments, provided that three out of the four fragments are above 6Mb, the translocation can be detected.

A review of, and commentary on, the ongoing second clinical introduction of preimplantation genetic screening (PGS) to routine IVF practice

PURPOSE

Current re-introduction of "improved" preimplantation genetic screening (PGS#2) raises the question whether PGS#2 is ready for routine clinical application.

METHODS

We assessed available evidence via review of published data for years 2005-2012, and review of currently ongoing registered clinical trials, based on searches under appropriate key words in PubMed, MEDLINE, Cochrane Database System Review and Google Scholar and http://www.ClinicalTrials.gov . In absence of prospective clinical trials, and due to limited available data, individual publications/ongoing studies are assessed.

RESULTS

PGS#2 offers significant improvements in accuracy of aneuploidy diagnosis over PGS#1. By moving embryo biopsy from day-3 after fertilization (6-8 cell stage) to trophectoderm biopsy at blastocyst stage (day 5-6), PGS#2, however, adds additional co-variables to the analysis of efficacy of the procedure, which have special relevance for women with diminished ovarian reserve (DOR), who usually produce small egg and embryo numbers. Limited published data, claiming efficacy of PGS#2, as well as ongoing clinical trials, do not consider these additional co-variables, do not analyze outcomes by intent to treat and, therefore, have to be considered biased in patient selection.

CONCLUSIONS

Here reached conclusions are based on absence of adequate data rather than affirmative outcome assessments. They, therefore, are subject to change at any future date with generation of significant new data. Premature introduction of PGS#1 caused significant damage to patients. As currently no reliable PGS#2 data are available to suggest improvements in IVF outcomes, to avoid a repeat of the PGS#1 experience, PGS#2 should be considered experimental until data show otherwise.

Preimplantation genetic diagnosis to improve pregnancy outcomes in subfertility

Pre-implantation genetic diagnosis provides prenatal genetic diagnosis before implantation, thus allowing detection of chromosomal abnormalities and their exclusion from embryo transfer in assisted reproductive technologies. Polar body, blastomere or trophectoderm can each be used to obtain requisite genetic or embryonic DNA. Pre-implantation genetic diagnosis for excluding unbalanced translocations is well accepted, and pre-implantation genetic diagnosis aneuploidy testing to avoid repeated pregnancy losses in couples having recurrent aneuploidy is efficacious in reducing miscarriages. Controversy remains about whether pre-implantation genetic diagnosis aneuploidy testing improves take home pregnancy rates, for which reason adherence to specific indications is recommended while the issue is being adjudicated. Current recommendations are for obligatory 24 chromosome testing, most readily using array comparative genome hybridisation.

Idiopathic recurrent miscarriage is caused mostly by aneuploid embryos

OBJECTIVE

To determine any beneficial effects of preimplantation genetic screening (PGS) of all chromosomes by array comparative genomic hybridization (aCGH), with either day 3 or blastocyst biopsy, for idiopathic recurrent pregnancy loss (RPL) patients compared with their expected loss rate.

DESIGN

Case series report.

SETTING

Multiple fertility centers.

PATIENT(S)

A total of 287 cycles of couples with idiopathic RPL (defined as two or more losses).

INTERVENTION(S)

PGS was done with day 3 biopsy (n = 193) or blastocyst biopsy (n = 94), followed by analysis with aCGH.

MAIN OUTCOME MEASURE(S)

Spontaneous abortion rate, euploidy rate.

RESULT(S)

A total of 2,282 embryos were analyzed, of which 35% were euploid and 60% were aneuploid. There were 181 embryo transfer cycles, of which 100 (55%) became pregnant with an implantation rate of 45% (136 sacs/299 replaced embryos) and 94 pregnancies (92%) were ongoing (past second trimester) or delivered. The miscarriage rate was found to be only 6.9% (7/102), compared with the expected rate of 33.5% in an RPL control population and 23.7% in an infertile control population.

CONCLUSION(S)

Current PGS results with aCGH indicate a significant decrease in the miscarriage rate of idiopathic RPL patients and high pregnancy rates. Furthermore, this suggests that idiopathic recurrent miscarriage is mostly caused by chromosomal abnormalities in embryos.

Increased incidence of mosaicism detected by FISH in murine blastocyst cultured in vitro

The majority of in-vitro-derived human preimplantation embryos are chromosomally abnormal but whether the same pattern exists in vivo is unknown. This would be impossible to demonstrate in humans. Hence we chose murine embryos to study this difference owing to their ease of manipulation and compared the incidence of mosaicism between in-vivo- and in-vitro-cultured embryos. Two groups of embryos were analysed. Group A (in vitro) were obtained 48h following superovulation and cultured in vitro until the blastocyst stage. Fluorescent in-situ hybridization (FISH) was performed at different stages that included the cleavage, morula and blastocyst stage. Group B (in vivo) were obtained on day 2 or day 5 and FISH was performed immediately without culture. There was an increase in chromosomal mosaicism seen from the cleavage stage up to the blastocyst stage in the in-vitro culture group. Overall chromosomal abnormality from day 3 to day 5 was found to be 30% (28/94) in group A. The incidence of chromosomal abnormalities in blastocysts from group B was significantly lower than group A blastocysts (8% (3/40) and 31% (20/64) respectively; P<0.05). These data show that in-vitro cultured embryos had a significantly higher incidence of mosaicisim in comparison with the in-vivo group. Cultured human embryos show high levels of chromosomal abnormalities but whether this is a pattern seen in all embryos or is the result of culture is unknown. To study this pattern we used mouse embryos and carried out chromosome analysis by fluorescent in-situ hybridization. We compared embryos that were cultured (in vitro) with those that were not (in vivo, i.e. grown exclusively in the mouse). We found that cultured embryos showed significantly higher chromosomal abnormalities as compared with in vivo embryos. This suggests that certain culture conditions are responsible for the high level of chromosomal abnormalities seen in these embryos, which should be investigated further.

Preimplantation genetic diagnosis at 20 years

First reported in 1990, PGD has evolved into a complementary form of prenatal diagnosis offering novel indications. DNA for PGD can be recovered with equal safety and facility from polar bodies I and II, blastomere (8 cell embryo) and trophectoderm (5-6 day blastocyst). Diagnostic accuracy is very high (>99%) for both chromosomal abnormalities and single gene disorders. Traditional application of FISH with chromosome specific probes for detecting aneuploidy and translocations may be replaced or complemented by array comparative genome hybridization (array CGH); biopsied embryos can now be cryopreserved (vitrification) while analysis proceeds in orderly fashion. PGD has been accomplished for over 200 different single gene disorders. Novel indications for PGD not readily applicable by traditional prenatal genetic diagnosis include avoiding clinical pregnancy termination, performing preconceptional diagnosis (polar body I), obtaining prenatal diagnosis without disclosure of prenatal genotype (nondisclosure), diagnosing adult-onset disorders particularly cancer, and identifying HLA compatible embryos suitable for recovering umbilical cord blood stem cells.

Aneuploidies of chromosomes 1, 4, and 6 are not compatible with human embryos' implantation

OBJECTIVE

To verify whether chromosomes 1, 4, and 6 have a role in determining oocyte viability.

DESIGN

Retrospective study.

SETTING

Reproductive Medicine Unit, Società Italiana Studi Medicina della Riproduzione, Bologna, Italy.

PATIENT(S)

Eighty-five patients with a normal karyotype who had undergone an assisted conception cycle with chromosomal analysis of first polar bodies for chromosomes 13, 15, 16, 18, 21, and 22 (first panel). A clinical pregnancy was obtained in 43 patients, whereas 42 patients were not pregnant.

INTERVENTION(S)

After conclusion of clinical pregnancies to delivery or abortion, first polar bodies from 85 patients were reanalyzed for chromosomes 1, 4, and 6 (second panel).

MAIN OUTCOME MEASURE(S)

Aneuploidy frequency, clinical pregnancy outcome.

RESULT(S)

The aneuploidy rate contributed by chromosome 1, 4, and 6 to the oocytes that were normal for the first panel was significantly higher in the nonpregnant patients (28%) versus the pregnant patients (11%), whereas no difference resulted between term pregnancies (11%) and abortions (10%). This trend was also observed when studying the first polar bodies from the oocytes that originated the transferred embryos. The frequency of aneuploidy for chromosomes 1 and 4 was comparable with that of chromosomes 15, 16, 21, and 22.

CONCLUSION(S)

Aneuploidy of chromosomes 1, 4, and 6 seems to be related to failed implantation and not to spontaneous abortions.

Role of Preimplantation Genetic Diagnosis (PGD) in Current Infertility Practice

Chromosome imbalances are the leading cause of pregnancy loss in humans and play major roles in male and female infertility. Within the past two decades, the development and application of preimplantation genetic diagnosis (PGD) has played an important role in infertility practices worldwide. The purpose of this review is to discuss, how PGD may be applied in combating numerical chromosomal abnormalities and in Robertsonian and reciprocal chromosome translocations. We shall consider prevalence and risk of each aberration, interchromosomal effects and rationale behind use of PGD in each case. Numerical chromosome abnormalities (aneuploidy and polyploidy) in particular affect a very high proportion of preimplantation embryos (~ 50%). Given that a majority of preimplantation embryos are aneuploid, PGD can be used to screen embryos and transfer euploid embryos to improve pregnancy rates and reduce spontaneous abortions. The rationale of utilize PGD to transfer only euploid embryos would seem sound, but controversies exist surrounding application of PGD for aneuploidy detection. To this end, we will discuss the dichotomy between favorable descriptive reports and less favorable randomized clinical trial data. This review will discuss the trend towards differing sources of embryonic DNA (e.g. polar body vs blastomere vs blastocyst) as well as development of novel technologies for 24 chromosomes analysis.