Methods for comprehensive chromosome screening of oocytes and embryos: capabilities, limitations, and evidence of validity

Nanopore sequencing for detecting reciprocal translocation carrier status in preimplantation genetic testing

BACKGROUND

Balanced reciprocal translocation (BRT) is one of the most common chromosomal abnormalities that causes infertility, recurrent miscarriage, and birth defects. Preimplantation genetic testing (PGT) is widely used to select euploid embryos for BRT carriers to increase the chance of a healthy live birth. Several strategies can be used to distinguish reciprocal translocation carrier embryos from those with a normal karyotype; however, these techniques are time-consuming and difficult to implement in clinical laboratories. In this study, nanopore sequencing was performed in two reciprocal translocation carriers, and the results were validated using the next-generation sequencing-based method named, "Mapping Allele with Resolved Carrier Status" (MaReCs).

RESULTS

The translocation breakpoints in both reciprocal translocation carriers were accurately identified by nanopore sequencing and were in accordance with the results obtained using MaReCs. More than one euploid non-balanced translocation carrier embryo was identified in both patients. Amniocentesis results revealed normal karyotypes, consistent with the findings by MaReCs and nanopore sequencing.

CONCLUSION

Our results suggest that nanopore sequencing is a powerful strategy for accurately distinguishing non-translocation embryos from translocation carrier embryos and precisely localizing translocation breakpoints, which is essential for PGT and aids in reducing the propagation of reciprocal translocation in the population.

Next-Generation Sequencing Is More Efficient at Detecting Mosaic Embryos and Improving Pregnancy Outcomes than Single-Nucleotide Polymorphism Array Analysis

We compared chromosomal mosaicism, detected by next-generation sequencing (NGS), during preimplantation genetic testing (PGT) with that detected by single-nucleotide polymorphism (SNP) array-based PGT to assess the pregnancy outcomes associated with both platforms in a retrospective cohort study of patients undergoing in vitro fertilization in a single university-based assisted reproduction center. In total, 6427 blastocysts biopsied from 1513 patients who underwent 2833 oocyte retrievals from January 2017 to February 2019 were identified. The incidence of mosaicism was significantly higher in the NGS-based PGT group than in the SNP array-based PGT group. Furthermore, some aneuploid specimens were affected by mosaicism. The total mosaicism detection rate with NGS-based PGT (23.3%) was significantly higher than that with SNP array-based PGT (7.7%). Mosaicism rates were similar when stratified by maternal age or PGT type. The SNP array cohort showed a significantly higher spontaneous abortion rate than the NGS cohort (10.07% versus 6.33%; P = 0.0403). The ongoing pregnancy/live birth rate was higher in the NGS cohort (44.1%) than in the SNP array cohort (42.28%). Our results confirm that NGS-based PGT can detect mosaicism more frequently than SNP array-based PGT in trophectoderm specimens. Therefore, clinical application of NGS for PGT may improve pregnancy outcomes compared with that of SNP array-based PGT. More detailed blastocyst detection and classification is necessary to prioritize embryo transfers.

A workflow for simultaneous DNA copy number and methylome analysis of inner cell mass and trophectoderm cells from human blastocysts

OBJECTIVE

To establish a workflow for isolating single trophectoderm (TE) and inner cell mass (ICM) cells and to simultaneously evaluate these cells for copy number variation (CNV) as well as methylome development.

DESIGN

Experimental.

SETTING

Academic medical center.

PATIENT(S)

Donated genetically abnormal blastocysts.

INTERVENTION(S)

Single cells were isolated, followed by bisulfite conversion and sequencing to identify CNV and methylome profiles.

MAIN OUTCOME MEASURE(S)

CNV and methylation profiling.

RESULT(S)

Two embryos were dissociated, isolating 46 single cells, with 17 ICM and 12 TE cells selected for further downstream analysis. Chromosome ploidies and embryo sex were concordant with the results from conventional aneuploidy testing. In 3 of the 29 cells, additional aneuploidies were discovered, indicating possible mosaicism undetected by routine preimplantation genetic testing for aneuploidy. CpG methylation frequency was higher in ICM cells compared with TE cells (44.3% vs. 32.4%), respectively, while non-CpG methylation frequency was similar among both cell types. CpG methylation levels accurately distinguished ICM from TE cells epigenetically.

CONCLUSION(S)

We describe an effective workflow for isolating and sequencing single ICM and TE cells from human blastocysts. The use of methylation profiling can help distinguish these two cell populations better then morphologic identification alone. TE cells had significantly lower levels of DNA methylation, which may be explained in part by the fact that these cells have begun the process of differentiation and are transcriptionally more active than ICM. This approach may be used to explore the genetic complexities within human embryos, specifically among the two primary cell types seen at this stage of development.

Long-read sequencing and haplotype linkage analysis enabled preimplantation genetic testing for patients carrying pathogenic inversions

Background

Preimplantation genetic testing (PGT) has already been applied in patients known to carry chromosomal structural variants to improve the clinical outcome of assisted reproduction. However, conventional molecular techniques are not capable of reliably distinguishing embryos that carry balanced inversion from those with a normal karyotype. We aim to evaluate the use of long-read sequencing in combination with haplotype linkage analysis to address this challenge.

Methods

Long-read sequencing on Oxford Nanopore platform was employed to identify the precise positions of inversion break points in four patients. Comprehensive chromosomal screening and genome-wide haplotype linkage analysis were performed based on SNP microarray. The haplotypes, including the break point regions, the whole chromosomes involved in the inversion and the corresponding homologous chromosomes, were established using informative SNPs.

Results

All the inversion break points were successfully identified by long-read sequencing and validated by Sanger sequencing, and on average only 13 bp differences were observed between break points inferred by long-read sequencing and Sanger sequencing. Eighteen blastocysts were biopsied and tested, in which 10 were aneuploid or unbalanced and eight were diploid with normal or balanced inversion karyotypes. Diploid embryos were transferred back to patients, the predictive results of the current methodology were consistent with fetal karyotypes of amniotic fluid or cord blood.

Conclusions

Nanopore long-read sequencing is a powerful method to assay chromosomal inversions and identify exact break points. Identification of inversion break points combined with haplotype linkage analysis is an efficient strategy to distinguish embryos with normal or balanced inversion karyotypes, facilitating PGT applications.

Performance of preimplantation genetic testing for aneuploidy in IVF cycles for patients with advanced maternal age, repeat implantation failure, and idiopathic recurrent miscarriage

OBJECTIVE

The primary objective of this study was to investigate whether preimplantation genetic testing for aneuploidy (PGT-A) of blastocysts through array comparative genomic hybridization (aCGH) improves live birth rates (LBR) in IVF cycles for patients with high prevalence of aneuploidy.

MATERIALS AND METHODS

This study included 1389 blastocysts with aCGH results derived from 296 PGT-A cycles in IVF patients with advanced maternal age (AMA) (n = 87, group A), those with repeated implantation failure (RIF) (n = 82, group B), those with recurrent miscarriage (RM) (n = 82, group C), and oocyte donors (OD) (n = 45, young age, as a control group). Another 61 AMA patients without PGT-A procedures were used as a control group for group A. Vitrification was performed after blastocyst biopsy, and thawed euploid embryos were transferred in a nonstimulated cycle.

RESULTS

For the AMA group, a significant increase in LBRs was found in the PGT-A group compared with the non-PGT-A group (54.1% vs. 32.8%, p = 0.018). Consistent LBRs (54.1%, 51.6%, 55.9%, and 57.1%, respectively, in group A, B, C, and young age group) were obtained for all the indications.

CONCLUSIONS

LBRs can be improved using PGT-A of blastocysts with aCGH in IVF cycles for patients with a high rate of aneuploidy, especially for patients with AMA.

Transition from blastomere to trophectoderm biopsy: comparing two preimplantation genetic testing for aneuploidies strategies

Shortly after the implementation of comprehensive chromosome screening (CCS) techniques for preimplantation genetic testing for aneuploidies (PGT-A), the discussion about the transition from day 3 to blastocyst stage biopsy was initiated. Trophectoderm biopsy with CCS is meant to overcome the limitations of cleavage-stage biopsy and single-cell analysis. The aim of this study was to assess the results obtained in our PGT-A programme after the implementation of this new strategy. Comparisons between the results obtained in 179 PGT-A cycles with day 3 biopsy (D+3) and fresh embryo transfer, and 204 cycles with trophectoderm biopsy and deferred (frozen–thawed) embryo transfer were established. Fewer embryos were biopsied and a higher euploidy rate was observed in the trophectoderm biopsy group. No differences in implantation (50.3% vs. 61.4%) and clinical pregnancy rate per transfer (56.1% vs. 65.3%) were found. Although the mean number of euploid embryos per cycle did not differ between groups (1.5 ± 1.7 vs. 1.7 ± 1.8), the final number of euploid blastocysts available for transfer per cycle was significantly higher in the trophectoderm biopsy group (1.1 ± 1.3 vs. 1.7 ± 1.8). This factor led to an increased cumulative live birth rate in this last group (34.1% vs. 44.6%). Although both strategies can offer good results, trophectoderm biopsy offers a more robust diagnosis and the intervention is less harmful for the embryos so more euploid blastocysts are finally available for transfer and/or vitrification.

Challenges facing contemporary preimplantation genetic screening

PURPOSE OF REVIEW

Aneuploidy is a leading cause of pregnancy failure. Although initial attempts to perform preimplantation genetic screening did not improve outcomes, validated techniques were developed to safely and effectively increase pregnancy rates. Still, many embryos designated as euploid do not implant. Current approaches are being refined to provide additional biologic insight into why this is the case. At present, the diagnosis and clinical relevance of segmental aneuploidy and mosaicism are amongst the more heavily investigated.

RECENT FINDINGS

Class I data have proven the safety of trophectoderm biopsy and validation studies have shown single nucleotide polymorphism array and quantitative PCR can accurately detect whole chromosome aneuploidy. Similar studies to validate next generation sequencing are underway. Although randomized control trials have demonstrated the clinical utility of preimplantation genetic screening, recent data on the impact of mosaicism and segmental aneuploidy require clarification.

SUMMARY

Several well powered randomized control trials have shown preimplantation genetic screening improves implantation rate. Plausible explanations for euploid failures include undetected mosaicism and segmental aneuploidy. However, the true incidence and dispersion of mosaicism within the embryo is unknown. Likewise, the resolution of detection and clinical significance of segmental aneuploidy is unclear. Further research to validate proposed detection algorithms and class I data to determine if detection impacts outcomes is needed.

Thirteen years' experience of 893 PGD cycles for monogenic disorders in a publicly funded, nationally regulated regional hospital service

This study provides an overview of preimplantation genetic diagnosis (PGD) for single gene diseases and the management of expanding indications in the context of a fully financially covered service at Montpellier's regional hospital centre. Within the framework of a restrictive law ruling PGD in France, only the parental genetic risk can be studied in embryos (concurrent aneuploidy screening is not allowed). PCR-based techniques were developed combining mutation detection and closely linked short tandem repeat markers within or flanking the affected genes, and set up more than 100 different robust fluorescent multiplex assays for 61 monogenic disorders. This strategy was used to analyse blastomeres from cleavage-stage embryos. Overall, 893 cycles were initiated in 384 couples; 727 cycles proceeded to oocyte retrieval and 608 cycles to embryo transfer, resulting in 184 deliveries. Clinical pregnancy rate per transfer, implantation and miscarriage rates were 33.6%, 25.1% and 8.8%, respectively. Our PGD programme resulted in the birth of 214 healthy babies for 162 out of 358 couples (45.3%), constituting a relevant achievement within an organizational framework that does not allow aneuploidy screening but provides equal access to PGD, both geographically and socioeconomically. This is a rare example of a fully free-of-charge PGD service.

Translocations, inversions and other chromosome rearrangements

Chromosomal rearrangements have long been known to significantly impact fertility and miscarriage risk. Advancements in molecular diagnostics are challenging contemporary clinicians and patients in accurately characterizing the reproductive risk of a given abnormality. Initial attempts at preimplantation genetic diagnosis were limited by the inability to simultaneously evaluate aneuploidy and missed up to 70% of aneuploidy in chromosomes unrelated to the rearrangement. Contemporary platforms are more accurate and less susceptible to technical errors. These techniques also offer the ability to improve outcomes through diagnosis of uniparental disomy and may soon be able to consistently distinguish between normal and balanced translocation karyotypes. Although an accurate projection of the anticipated number of unbalanced embryos is not possible at present, confirmation of normal/balanced status results in high pregnancy rates (PRs) and diagnostic accuracy.

Pre-implantation genetic testing in ART: who will benefit and what is the evidence?

Pre-implantation genetic diagnosis for aneuploidy testing (PGD-A) is a tool to identify euploid embryos during IVF. The suggested populations of patients that can benefit from it are infertile women of advanced maternal age, with a history of recurrent miscarriages and/or IVF failures. However, a general consensus has not yet been reached.After the clinical failure of its first version based on cleavage stage biopsy and 9 chromosome-FISH analysis, PGD-A is currently performed by 24 chromosome screening techniques on trophectoderm (TE) biopsies. This approach has been clearly demonstrated to involve a higher clinical efficiency with respect to the standard care, in terms of sustained pregnancy rate per transfer and lower miscarriage rate. However, data about PGD-A efficacy calculated on a per intention-to-treat basis, as well as an analysis of its cost-effectiveness, are still missing.TE biopsy is a safe and extensively validated approach with low biological and technical margin of error. Firstly, the prevalence of mosaic diploid/aneuploid blastocysts is estimated to be between 0 and 16 %, thus largely tolerable. Secondly, all the comprehensive chromosome screening (CCS) technologies adapted to, or designed to conduct PGD-A are highly concordant, and qPCR in particular has been proven to show the lowest false positive error rate (0.5 %) and a clinically recognizable error rate per blastocyst of just 0.21 %.In conclusion, there is a sufficient body of evidence to support the clinical application of CCS-based PGD-A on TE biopsies. The main limiting factor is the need for a high-standard laboratory to conduct blastocyst culture, biopsy and vitrification without impacting embryo viability.

SNP array-based analyses of unbalanced embryos as a reference to distinguish between balanced translocation carrier and normal blastocysts

Purpose

The purpose of the study is to validate a method that provides the opportunity to distinguish a balanced translocation carrier embryo from a truly normal embryo in parallel with comprehensive chromosome screening (CCS).

Methods

A series of translocation carrier couples that underwent IVF with single nucleotide polymorphism (SNP) array-based CCS on 148 embryos were included. Predictions of balanced or normal status of each embryo were made based upon embryonic SNP genotypes. In one case, microdeletion status was used to designate whether embryos were balanced or normal. In 10 additional cases, conventional karyotyping was performed on newborns in order to establish the true genetic status (balanced or normal) of the original transferred embryo. Finally, implantation potential of balanced or normal embryos was compared.

Results

Phasing SNPs using unbalanced embryos allowed accurate prediction of whether transferred embryos were balanced translocation carriers or truly normal in all cases completed to date (100 % concordance with conventional karyotyping of newborns). No difference in implantation potential of balanced or normal embryos was observed.

Conclusions

This study demonstrates the validity of a CCS method capable of distinguishing normal from balanced translocation carrier embryos. The only prerequisite is the availability of parental DNA and an unbalanced IVF embryo, making the method applicable to the majority of carrier couples. In addition, the SNP array platform allows simultaneous CCS for aneuploidy with the same platform and from the same biopsy. Future work will involve prospective predictions to select normal embryos with subsequent karyotyping of the resulting newborns.

Effects of maternal age on euploidy rates in a large cohort of embryos analyzed with 24-chromosome single-nucleotide polymorphism-based preimplantation genetic screening

OBJECTIVE

To determine the effect of maternal age on the average number of euploid embryos retrieved during oocyte harvest as part of an in vitro fertilization (IVF) cycle, including the probability of retrieving at least one euploid embryo in a cohort (PrE).

DESIGN

Retrospective study.

SETTING

Preimplantation genetic screening (PGS) laboratory.

PATIENT(S)

Women aged 18 to 48 years undergoing IVF treatment.

INTERVENTION(S)

Use of 24-chromosome single-nucleotide polymorphism (SNP)-based PGS of day-3 and day-5 embryo biopsies.

MAIN OUTCOME MEASURE(S)

Relationships between maternal age and the rate of embryos that tested as euploid (hereafter referred to as "euploid embryos"), the average number and proportion of euploid embryos per IVF cycle, and PrE.

RESULT(S)

We analyzed 22,599 day-3 embryos and 15,112 day-5 embryos. In women aged 27 to 35 years, the median proportion of euploid embryos in each cycle remained constant at ∼35% in day-3 biopsies and ∼55% in day-5 biopsies, but it decreased rapidly after age 35. On average, women in their late 20s had four euploid embryos (day 3 or day 5) per cycle, but this number decreased linearly (R(2) ≥ 0.983) after 35 years of age. The effect of maternal age on PrE was similar, with a rapid exponential decline (R(2) = 0.986). Across all maternal ages, the euploid proportion and number of embryos per cycle were counterbalanced, so the number of euploid embryos per cycle was the same for day-3 and day-5 biopsies. This suggests that the loss of embryos from day 3 to day 5 was primarily due to aneuploidy.

CONCLUSION(S)

Our results confirm the known inverse relationship between advanced maternal age (>35 years) and embryo euploidy, demonstrating that equal numbers of euploid embryos are available at day 3 and day 5.

Omics in Reproductive Medicine: Application of Novel Technologies to Improve the IVF Success Rate

Treatment for many infertile couples often consists of in vitro fertilization (IVF) but an estimated 70% of IVF cycles fail to produce a live birth. In an attempt to improve the live birth rate, the vast majority of IVF cycles performed in the United States involve the transfer of multiple embryos, a practice that increases the risk of multiple gestation pregnancy. This is a concern because multiple gestation pregnancies are associated with an increased incidence of maternal and fetal complications and significant cost associated with the care of preterm infants. As the ideal outcome of each IVF cycle is the birth of a single healthy baby, significant effort has focused on identifying embryos with the greatest developmental potential. To date, selection of euploid embryos using comprehensive chromosome screening (CCS) is the most promising approach while metabolomic and proteomic assessment of spent culture medium have the potential to noninvasively assess embryo viability. Endometrial gene expression profiling may help determine the optimal time to perform embryo transfer. While CCS has been implemented in some clinics, further development and optimization will be required before analysis of spent culture medium and endometrial gene expression profiling make the transition to clinical use. This review will describe efforts to identify embryos with the greatest potential to result in a healthy, live birth, with a particular emphasis on detection of embryo aneuploidy and metabolic profiling of spent embryo culture medium. Assessment of endometrial receptivity to identify the optimal time to perform embryo transfer will also be discussed.

Impact of sperm genome decay on Day-3 embryo chromosomal abnormalities from advanced-maternal-age patients

Infertile male patients often exhibit unconventional semen parameters, including DNA fragmentation, chromatin dispersion, and aneuploidy-collectively referred to as sperm genome decay (SGD). We investigated the correlation of SGD to embryo chromosomal abnormalities and its effect on clinical pregnancy rates in patients with advanced maternal age (AMA) (>40 years) who were undergoing intracytoplasmic sperm injection-preimplantation genetic screening (ICSI-PGS). Three groups were assessed: patients with AMA and male partners with normal sperm (AMA-N); AMA patients and male partners presenting with SGD (AMA-SGD); and young fertile female patients and male partners with SGD (Y-SGD). We found a significant increase in embryonic chromosomal abnormalities-polyploidy, nullisomy, mosaicism, and chaotic anomaly rates-when semen parameters are altered (76% vs. 67% and 66% in AMA-SGD vs. AMA-N and Y-SGD groups, respectively). Statistical analysis showed a correlation between SGD and aneuploidies of embryonic chromosomes 13, 16, 21, X, and Y, as well as negative clinical outcomes. Incorporation of molecular sperm analyses should therefore significantly minimize the risk of transmission of chromosomal anomalies from spermatozoa to embryos, and may provide better predictors of pregnancy than conventional sperm analyses. We also demonstrated that an ICSI-PGS program should be implemented for SGD patients in order to limit transmission of chromosomal paternal anomalies and to improve clinical outcome.

Preimplantation genetic screening of blastocysts by multiplex qPCR followed by fresh embryo transfer: validation and verification

Background

Aneuploidy is an important etiology of implantation failure and quantitative real-time polymerase chain reaction (qPCR) seems a promising preimplantation genetic screening (PGS) technology to detect aneuploidies. This verification study aimed at verifying the impact on reproductive outcomes in in vitro fertilization (IVF) cycles using fresh embryo transfer (FET) in which the embryos were selected by blastocyst biopsy with qPCR-based PGS in our settings.

Results

A total of 13 infertile couples with more than once failed in vitro fertilization were enrolled during July to October of 2014. PGS was conducted by qPCR with selectively amplified markers to detect common aneuploidies (chromosomes 13, 18, 21, X, and Y). The design of the qPCR molecular markers adopted the locked nucleic acid (LNA) strategy. The blastocyst biopsy was performed on Day 5/6 and the PGS was done on the same day, which enabled FET. A total of 72 blastocysts were biopsied. Successful diagnoses were established in all embryos and the rate of successful diagnosis was 100 %. The aneuploidy rate was 38.9 % (28/72). 28 embryos were transferred. The clinical pregnancy rate was 61.5 % (8/13) per cycle. Early first trimester abortion was encountered in 1 and the ongoing pregnancy rate was 53.8 % (7/13) per cycle.

Conclusion

This study verified the favorable outcome of adopting PGS with qPCR + FET in our own setting. Expanding the repertoire of aneuploidies being investigated (from a limited set to all 24 chromosomes) is underway and a randomized study by comparing qPCR and other PGS technologies is warranted.

Electronic supplementary material

The online version of this article (doi:10.1186/s13039-015-0140-9) contains supplementary material, which is available to authorized users.

Diagnosis of human preimplantation embryo viability

BACKGROUND

Transfer of more than a single embryo in an IVF cycle comes with the finite possibility of a multiple gestation. Even a twin pregnancy confers significant risk to both mother and babies. The move to single-embryo transfer for all patients will be greatly facilitated by the ability to quantify embryo viability. Developments in time-lapse incubation systems have provided new insights into the developmental kinetics of the human preimplantation embryo. Advances in molecular methods of chromosomal analysis have created platforms for highly effective screening of biopsied embryos, while noninvasive analysis of embryo physiology reveals more about the embryo than can be determined by morphology alone.

METHODS

Recent developments in time-lapse microscopy, molecular karyotyping and in proteomics and metabolomics have been assessed and presented here in a descriptive review.

RESULTS AND CONCLUSIONS

New algorithms are being created for embryo selection based on their developmental kinetics in culture, and the impact of factors such as patient etiology and treatment are being clarified. Potential links between morphokinetic data and embryo karyotype are being elucidated. The introduction of new molecular methods of determining embryo chromosomal complement is proving to be accurate and reproducible, with the future trending toward CGH arrays or next generation sequencing as a rapid and reliable means of analysis, that should be suitable for each IVF clinic to adopt. A relationship between embryo metabolism and viability is established and is now being considered together with morphokinetic data to create more robust algorithms for embryo selection. Microfluidic devices have the capacity and potential to be used in human IVF clinics for the routine diagnosis of embryo biomarkers.

Embryonic aneuploidy: overcoming molecular genetics challenges improves outcomes and changes practice patterns

Since its inception, in vitro fertilization (IVF) has pursued molecular technology to improve patient outcomes, leading to enhanced methods of embryo selection. Comprehensive chromosomal screening (CCS) is a powerful tool that decreases maternal and neonatal morbidity due to multiple gestations by allowing the transfer of fewer embryos while maintaining success rates. To optimize this genetic test, physiological principles limiting the timing and type of cells to be removed had to be realized. Molecular barriers involved in genome amplification and ensuring the accuracy and validity of the CCS platform required a multistep approach to ensure that this technology was not used prematurely. Only after ensuring that the potential for harm was minimized and benefit maximized could clinicians use this technology to improve patient care.

Mild ovarian stimulation for in vitro fertilization: one perspective from the USA

PURPOSE

To provide a perspective regarding mild ovarian stimulation, taking into account particular issues relevant in the United States

METHODS

Literature review and editorial commentary

RESULTS

Mild ovarian stimulation for IVF has some proven and some theoretical advantages over conventional stimulation, such as lower risk of ovarian hyperstimulation syndrome and lower cost per fresh IVF cycle. However, cumulative live birth rate, including transfers from fresh and frozen embryos, is likely to be lower with mild stimulation. The cost-effectiveness of mild stimulation IVF in the United States has not been established.

CONCLUSIONS

Mild ovarian stimulation is an appropriate option to consider for certain patient groups or based on patient preference. However, significant potential disadvantages limit its widespread acceptability for patients in the United States at this time.

Morphological systems of human embryo assessment and clinical evidence

Success rates with IVF have improved remarkably since the procedure was first established for clinical use with the first successful birth in 1978. The main goals today are to perform single-embryo transfer in order to prevent multiple pregnancies and achieve higher overall pregnancy rates. However, the ability to identify the most viable embryo in a cohort remains a challenge despite the numerous scoring systems currently in use. Clinicians still depend on developmental rate and morphological assessment using light microscopy as the first-line approach for embryo selection. Active research in the field involves developing non-invasive methods for scoring embryos and ranking them according to their ability to implant and give rise to a healthy birth. Current attention is particularly being focused on time-lapse evaluation. Available data from preliminary studies indicate that these systems are safe;prospective data now need to be collected to determine whether these methods do improve implantation rates. This review gives brief consideration to the use of morphological evaluations in assisted reproduction treatment, discusses the types of embryo scoring,digital imaging and biometric approaches currently in use and comments on future developments for embryo evaluation.

Comprehensive genetic assessment of the human embryo: can empiric application of microarray comparative genomic hybridization reduce multiple gestation rate by single fresh blastocyst transfer?

PURPOSE

The unacceptable multiple gestation rate currently associated with in vitro fertilization (IVF) would be substantially alleviated if the routine practice of transferring more than one embryo were reconsidered. While transferring a single embryo is an effective method to reduce the clinical problem of multiple gestation, rigid adherence to this approach has been criticized for negatively impacting clinical pregnancy success in IVF. In general, single embryo transfer is viewed cautiously by IVF patients although greater acceptance would result from a more effective embryo selection method.

METHODS

Selection of one embryo for fresh transfer on the basis of chromosomal normalcy should achieve the dual objective of maintaining satisfactory clinical pregnancy rates and minimizing the multiple gestation problem, because embryo aneuploidy is a major contributing factor in implantation failure and miscarriage in IVF. The initial techniques for preimplantation genetic screening unfortunately lacked sufficient sensitivity and did not yield the expected results in IVF. However, newer molecular genetic methods could be incorporated with standard IVF to bring the goal of single embryo transfer within reach.

RESULTS

Aiming to make multiple embryo transfers obsolete and unnecessary, and recognizing that array comparative genomic hybridization (aCGH) will typically require an additional 12 h of laboratory time to complete, we propose adopting aCGH for mainstream use in clinical IVF practice.

CONCLUSION

As aCGH technology continues to develop and becomes increasingly available at lower cost, it may soon be considered unusual for IVF laboratories to select a single embryo for fresh transfer without regard to its chromosomal competency. In this report, we provide a rationale supporting aCGH as the preferred methodology to provide a comprehensive genetic assessment of the single embryo before fresh transfer in IVF. The logistics and cost of integrating aCGH with IVF to enable fresh embryo transfer are also discussed.