Blastomere biopsy for PGD delays embryo compaction and blastulation: a time-lapse microscopic analysis

Blastocoel fluid as an alternative source of DNA for minimally invasive PGT and biomarker of embryo competence

The discovery of DNA in blastocoel fluid (BF-DNA) generated new perspectives in the potential development of simpler and safer alternative non-invasive tests in reproductive genetics. Short DNA fragments of apoptotic origin, together with specific expression patterns of pro- and anti-apoptotic genes in the blastocoel fluid of euploid and aneuploid embryos, suggest a self-correction mechanism to preferentially eliminate aneuploid cells, and purge defective and non-viable cells. The correlation of blastocoel fluid content with the genetic status of the whole embryo, and therefore its potential use in minimally invasive preimplantation genetic testing (miPGT), or as an indicator of embryo potential, remains uncertain and needs to be determined. The limited amount and compromised integrity of BF-DNA, with likely apoptotic origination, constrains its amplification, leading to low concordance and reproducibility rates for both aneuploidy screening and monogenic testing. While embryo genotyping constitutes a more ambitious goal, the presence of analysable DNA after amplification in blastocoel fluid may be used as a clinical biomarker of embryo competency to select the most viable embryo(s) for transfer, and potentially improve the implantation rate. Although blastocentesis remains a promising area for future research, several technical and methodological limitations are currently constraining its consideration for clinical practice.

Preimplantation genetic testing in the current era, a review

BACKGROUND

Preimplantation genetic testing (PGT), also referred to as preimplantation genetic diagnosis (PGD), is an advanced reproductive technology used during in vitro fertilization (IVF) cycles to identify genetic abnormalities in embryos prior to their implantation. PGT is used to screen embryos for chromosomal abnormalities, monogenic disorders, and structural rearrangements.

DEVELOPMENT OF PGT

Over the past few decades, PGT has undergone tremendous development, resulting in three primary forms: PGT-A, PGT-M, and PGT-SR. PGT-A is utilized for screening embryos for aneuploidies, PGT-M is used to detect disorders caused by a single gene, and PGT-SR is used to detect chromosomal abnormalities caused by structural rearrangements in the genome.

PURPOSE OF REVIEW

In this review, we thoroughly summarized and reviewed PGT and discussed its pros and cons down to the minutest aspects. Additionally, recent studies that highlight the advancements of PGT in the current era, including their future perspectives, were reviewed.

CONCLUSIONS

This comprehensive review aims to provide new insights into the understanding of techniques used in PGT, thereby contributing to the field of reproductive genetics.

Evolution of Minimally Invasive and Non-Invasive Preimplantation Genetic Testing: An Overview

Preimplantation genetic testing (PGT) has become a common supplementary diagnοstic/testing tοol for in vitro fertilization (ΙVF) cycles due to a significant increase in cases of PGT fοr mοnogenic cοnditions (ΡGT-M) and de novο aneuplοidies (ΡGT-A) over the last ten years. This tendency is mostly attributable to the advancement and application of novel cytogenetic and molecular techniques in clinical practice that are capable of providing an efficient evaluation of the embryonic chromosomal complement and leading to better IVF/ICSI results. Although PGT is widely used, it requires invasive biopsy of the blastocyst, which may harm the embryo. Non-invasive approaches, like cell-free DNA (cfDNA) testing, have lower risks but have drawbacks in consistency and sensitivity. This review discusses new developments and opportunities in the field of preimplantation genetic testing, enhancing the overall effectiveness and accessibility of preimplantation testing in the framework of developments in genomic sequencing, bioinformatics, and the integration of artificial intelligence in the interpretation of genetic data.

Artificial intelligence in time-lapse system: advances, applications, and future perspectives in reproductive medicine

With the rising demand for in vitro fertilization (IVF) cycles, there is a growing need for innovative techniques to optimize procedure outcomes. One such technique is time-lapse system (TLS) for embryo incubation, which minimizes environmental changes in the embryo culture process. TLS also significantly advances predicting embryo quality, a crucial determinant of IVF cycle success. However, the current subjective nature of embryo assessments is due to inter- and intra-observer subjectivity, resulting in highly variable results. To address this challenge, reproductive medicine has gradually turned to artificial intelligence (AI) to establish a standardized and objective approach, aiming to achieve higher success rates. Extensive research is underway investigating the utilization of AI in TLS to predict multiple outcomes. These studies explore the application of popular AI algorithms, their specific implementations, and the achieved advancements in TLS. This review aims to provide an overview of the advances in AI algorithms and their particular applications within the context of TLS and the potential challenges and opportunities for further advancements in reproductive medicine.

Development of preimplantation genetic testing for monogenic diseases in China

Preimplantation genetic testing for monogenic diseases (PGT-M) can effectively interrupt the transmission of genetic diseases from parents to the offspring before pregnancy. In China, there are over ten million individuals afflicted with monogenic disorders. This literature review summarizes the development of PGT-M in China for the past 24 years, covering the general steps such as the indications and contraindications, genetic and reproductive counselling, biopsy methods, detecting techniques and strategies during PGT-M application in China. The ethical considerations of PGT-M are also be emphasized, including sexual selection, transferring for mosaic embryos, the three-parent baby, and the different opinions for serious adult-onset conditions. Some key policies of the Chinese government for the application of PGT-M are also considered. Methods for regulation of this technique, as well as specific management to increase the accuracy and reliability of PGT-M, are regarded as priority issues in China. The third-generation sequencing and variants testing from RNA level, and non-invasive preimplantation genetic testing using blastocoel fluid and free DNA particles within spent blastocyst medium might be potential techniques and strategies for PGT-M in future.

Time-lapse monitoring: An adjunct tool to select embryos for preimplantation genetic testing

The goal for the present study was to investigate the effect of aneuploidy on embryo morphokinetics events in a time-lapse imaging (TLI) system incubator. This retrospective cohort study was performed in a private university-affiliated in vitro fertilization center, between 2019 March and December 2020. Kinetic data were analyzed in 935 embryos, derived from 316 patients undergoing intracytoplasmic sperm injection cycle with preimplantation genetic testing (PGT) for aneuploidy, individually cultured in a TLI incubator until Day 5 of development. Timing of morphokinetic variables, the incidences of multinucleation, and Known Implantation Data Score (KIDScore)-Day 5 were compared between euploid (n = 352) and aneuploid embryos (n = 583). Aneuploid embryos showed significantly longer timing to complete specific morphokinetic parameters compared to euploidy embryos. Euploidy embryos also showed a significantly higher KIDScore when compared with the aneuploidy ones. Our evidence suggests that TLI monitoring may be an adjunct approach to select embryos for PGT; however, cautious investigation is still needed.

PGT-A is associated with reduced cumulative live birth rate in first reported IVF stimulation cycles age ≤ 40: an analysis of 133,494 autologous cycles reported to SART CORS

PURPOSE

To evaluate the impact of preimplantation genetic testing for aneuploidy (PGT-A) on cumulative live birth rate (CLBR) in IVF cycles.

METHODS

Retrospective cohort study of the SART CORS database, comparing CLBR for patients using autologous oocytes, with or without PGT-A. The first reported autologous ovarian stimulation cycle per patient between January 1, 2014, and December 31, 2015, and all linked embryo transfer cycles between January 1, 2014, and December 31, 2016, were included in the study. Exclusion criteria were donor oocyte cycles, donor embryo cycles, gestational carrier cycles, cycles which included both a fresh embryo transfer (ET) combined with a thawed embryo previously frozen (ET plus FET), or cycles with a fresh ET after PGT-A.

RESULTS

A total of 133,494 autologous IVF cycles were analyzed. Amongst patients who had blastocysts available for either ET or PGT-A, including those without transferrable embryos, decreased CLBR was noted in the PGT-A group at all ages, except ages > 40 (p < 0.01). A subgroup analysis of only those patients who had PGT-A and a subsequent FET, excluding those without transferrable embryos, demonstrated a very high CLBR, ranging from 71.2% at age < 35 to 50.2% at age > 42. Rates of multiple gestations, preterm birth, early pregnancy loss, and low birth weight were all greater in the non-PGT-A group.

CONCLUSIONS

PGT-A was associated with decreased CLBR amongst all patients who had blastocysts available for ET or PGT-A, except those aged > 40. The negative association of PGT-A use and CLBR per cycle start was especially pronounced at age < 35.

An Update on Non-invasive Approaches for Genetic Testing of the Preimplantation Embryo

Preimplantation Genetic Testing (PGT) aims to reduce the chance of an affected pregnancy or improve success in an assisted reproduction cycle. Since the first established pregnancies in 1990, methodological approaches have greatly evolved, combined with significant advances in the embryological laboratory. The application of preimplantation testing has expanded, while the accuracy and reliability of monogenic and chromosomal analysis have improved. The procedure traditionally employs an invasive approach to assess the nucleic acid content of embryos. All biopsy procedures require high technical skill, and costly equipment, and may impact both the accuracy of genetic testing and embryo viability. To overcome these limitations, many researchers have focused on the analysis of cell-free DNA (cfDNA) at the preimplantation stage, sampled either from the blastocoel or embryo culture media, to determine the genetic status of the embryo non-invasively. Studies have assessed the origin of cfDNA and its application in non-invasive testing for monogenic disease and chromosomal aneuploidies. Herein, we discuss the state-of-the-art for modern non-invasive embryonic genetic material assessment in the context of PGT. The results are difficult to integrate due to numerous methodological differences between the studies, while further work is required to assess the suitability of cfDNA analysis for clinical application.

Non-Invasive Preimplantation Genetic Testing for Aneuploidy and the Mystery of Genetic Material: A Review Article

This review focuses on recent findings in the preimplantation genetic testing (PGT) of embryos. Different preimplantation genetic tests are presented along with different genetic materials and their analysis. Original material concerning preimplantation genetic testing for aneuploidy (PGT-A) was sourced by searching the PubMed and ScienceDirect databases in October and November 2021. The searches comprised keywords such as ‘preimplantation’, ‘cfDNA’; ‘miRNA’, ‘PGT-A’, ‘niPGT-A’, ‘aneuploidy’, ‘mosaicism’, ‘blastocyst biopsy’, ‘blastocentesis’, ‘blastocoel fluid’, ‘NGS’, ‘FISH’, and ‘aCGH’. Non-invasive PGT-A (niPGT-A) is a novel approach to the genetic analysis of embryos. The premise is that the genetic material in the spent embryo culture media (SECM) corresponds to the genetic material in the embryo cells. The limitations of niPGT-A are a lower quantity and lesser quality of the cell-free genetic material, and its unknown origin. The concordance rate varies when compared to invasive PGT-A. Some authors have also hypothesized that mosaicism and aneuploid cells are preferentially excluded from the embryo during early development. Cell-free genetic material is readily available in the spent embryo culture media, which provides an easier, more economic, and safer extraction of genetic material for analysis. The sampling of the SECM and DNA extraction and amplification must be optimized. The origin of the cell-free media, the percentage of apoptotic events, and the levels of DNA contamination are currently unknown; these topics need to be further investigated.

New insights regarding origin of monosomy occurrence in early developing embryos as demonstrated in preimplantation genetic testing

Introduction

Analyses of miscarriage products indicate that the majority of aneuploidies in early developing embryos derive from errors occurring during maternal meiosis and the paternal contribution is less than 10%. Our aim was to assess the aneuploidy (mainly monosmies) frequencies at the earliest stages of embryo development, 3 days following fertilization during In vitro fertilization (IVF) treatments and to elucidate their parental origin. Later, we compared monosomies rates of day 3 to those of day 5 as demonstrated from Preimplantation Genetic Testing for Structural chromosomal Rearrangement (PGT-SR) results.

Methods

For a retrospective study, we collected data of 210 Preimplantation Genetic Testing for Monogenic Disorder (PGT-M) cycles performed between years 2008 and 2019.This study includes 2083 embryos, of 113 couples. It also included 432 embryos from 90 PGT-SR cycles of other 45 patients, carriers of balanced translocations. Defining the parental origin of aneuploidy in cleavage stage embryos was based on haplotypes analysis of at least six informative markers flanking the analyzed gene. For comprehensive chromosomal screening (CCS), chromosomal microarray (CMA) and next generation sequencing (NGS) was used.

Results

We inspected haplotype data of 40 genomic regions, flanking analyzed genes located on 9 different chromosomes.151 (7.2%) embryos presented numerical alterations in the tested chromosomes. We found similar paternal and maternal contribution to monosomy at cleavage stage. We demonstrated paternal origin in 51.5% of the monosomy, and maternal origin in 48.5% of the monosomies cases.

Conclusion

In our study, we found equal parental contribution to monosomies in cleavage-stage embryos. Comparison to CCS analyses of PGT-SR patients revealed a lower rate of monosomy per chromosome in embryos at day 5 of development. This is in contrast to the maternal dominancy described in studies of early miscarriage. Mitotic errors and paternal involvement in chemical pregnancies and IVF failure should be re-evaluated. Our results show monosomies are relatively common and may play a role in early development of ART embryos.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13039-022-00582-5.

Different Strategies of Preimplantation Genetic Testing for Aneuploidies in Women of Advanced Maternal Age: A Systematic Review and Meta-Analysis

Background: Preimplantation genetic testing for aneuploidies (PGT-A) is widely used in women of advanced maternal age (AMA). However, the effectiveness remains controversial. Method: We conducted a comprehensive literature review comparing outcomes of IVF with or without PGT-A in women of AMA in PubMed, Embase, and the Cochrane Central Register of Controlled Trials in January 2021. All included trials met the criteria that constituted a randomized controlled trial for PGT-A involving women of AMA (≥35 years). Reviews, conference abstracts, and observational studies were excluded. The primary outcome was the live birth rate in included random control trials (RCTs). Results: Nine randomized controlled trials met our inclusion criteria. For techniques of genetic analysis, three trials (270 events) performed with comprehensive chromosomal screening showed that the live birth rate was significantly higher in the women randomized to IVF/ICSI with PGT-A (RR = 1.30, 95% CI 1.03–1.65), which was not observed in six trials used with FISH as well as all nine trials. For different stages of embryo biopsy, only the subgroup of blastocyst biopsy showed a higher live birth rate in women with PGT-A (RR = 1.36, 95% CI 1.04–1.79). Conclusion: The application of comprehensive chromosome screening showed a beneficial effect of PGT-A in women of AMA compared with FISH. Moreover, blastocyst biopsy seemed to be associated with a better outcome than polar body biopsy and cleavage-stage biopsy.

The dawn of the future: 30 years from the first biopsy of a human embryo. The detailed history of an ongoing revolution

Following early studies showing no adverse effects, cleavage stage biopsy by zona drilling using acid Tyrode's solution, and removal of single blastomeres for preimplantation genetic testing (PGT) and identification of sex in couples at risk of X-linked disease, was performed by Handyside and colleagues in late 1989, and pregnancies reported in 1990. This method was later used for specific diagnosis of monogenic conditions, and a few years later also for chromosomal structural and/or numerical impairments, thereby establishing a valuable alternative option to prenatal diagnosis. This revolutionary approach in clinical embryology spread worldwide, and several other embryo biopsy strategies developed over three decades in a process that is still ongoing. The rationale of this narrative review is to outline the different biopsy approaches implemented across the years in the workflow of the IVF clinics that provided PGT: their establishment, the first clinical experiences, their downsides, evolution, improvement and standardization. The history ends with a glimpse of the future: minimally/non-invasive PGT and experimental embryo micromanipulation protocols. This grand theme review outlines a timeline of the evolution of embryo biopsy protocols, whose implementation is increasing worldwide together with the increasing application of PGT techniques in IVF. It represents a vade mecum especially for the past, present and upcoming operators and experts in this field to (re)live this history from its dawn to its most likely future.

[Pre-implantation genetic testing: Comparison between cleavage stage and blastocyst biopsy]

OBJECTIVES

Preimplantation genetic testing (PGT) refers to the set of techniques for testing whether embryos obtained through in vitro fertilization have genetic defect. There is a lack of global standardization regarding practices between countries or even from one center to another. In ours, biopsies are preferably performed on day 3 embryos, but also at the blastocyst stage on day 5. The blastocyst biopsy often requires systematic freezing of the embryos before obtaining the genetic results, whereas day 3 biopsy allows fresh embryo transfer of the healthy or balanced embryo after getting the genetic results. We wanted to compare the chances of success for couples performing PGT in our center according to the day of the biopsy.

METHODS

For this, we carried out a retrospective monocentric study including all PGT cycles performed between 2016 and 2019 divided into two groups: day 3 or day 5 biopsy.

RESULTS

There was no significant difference in terms of live birth rate (P=0.7375) after fresh embryo transfers, as well for pregnancy rates, clinical pregnancy rates, implantation rates and miscarriage rates. On the other hand, we observed higher live birth rates after frozen-thawed embryo transfer when the biopsy was performed on day 5 rather on day 3 (P=0.0001). We also wanted to assess what was the most efficient biopsy strategy in our laboratory. Our rates of useful embryos were similar regardless of the day of the biopsy (34% in D3 and 37.7% in D5, P=0.244). No statistical difference was found in the number of unnecessarily biopsied embryos in the two groups. But still, the percentage of embryos biopsied on D5 and immediately frozen was 42.8% (118 blastocysts), while no embryo biopsied on D3 led to this case.

CONCLUSION

Therefore, our results are in favor of generalization of the D5 biopsy as the international standard. However, the organizational, financial and logistical implications that this technic would impose make it unsystematic in our center.

Modification of late human embryo development after blastomere removal on day 3 for preimplantation genetic testing

The purpose of our study was to use a time-lapse monitoring (TLM) system to determine if day 3 blastomere biopsy for preimplantation genetic testing (PGT) had an impact on subsequent morphokinetic parameters at the morula and blastocyst stages. In this retrospective monocentric study conducted between May 2013 and August 2017, we compared late morphokinetic parameters in embryos undergoing day 3 blastomere biopsy for PGT and in control non-biopsied embryos obtained in intracytoplasmic sperm injection (ICSI) cycles for male infertility. All embryos in both groups were cultured in a TLM system. The biopsy group was composed of 1691 embryos (386 PGT cycles). The control group was composed of 2578 embryos (786 ICSI cycles). Early morphokinetic parameters up to day 3 were similar in both groups. Concerning late morphokinetic parameters, the onset of compaction (tSC), fully-compacted morula stage (tM), onset of cavitation/early blastulation (tSB), and blastocyst stages (tB and tEB) appeared significantly earlier in the biopsy group than in the control group. We found that late morphokinetic events at the morula and the blastocyst stages occurred significantly earlier in biopsied embryos than in control non-biopsied-embryos. The mechanisms underlying these modifications of embryo development after biopsy should be investigated in order to determine precisely, and this phenomenon could be associated with embryo, fetal, and offspring development.Abbreviations: TLM: time-lapse monitoring; PGT: preimplantation genetic testing; ICSI: intracytoplasmic sperm injection; tSC: the onset of compaction; tM: fully-compacted morula stage; tSB: onset of cavitation/early blastulation; tB and tEB: blastocyst stages; OHSS: ovarian hyperstimulation syndrome.

Diagnostic efficiency of blastocyst culture medium in noninvasive preimplantation genetic testing

Objective

To evaluate the diagnostic efficiency of spent blastocyst culture medium (BCM) in noninvasive preimplantation genetic testing (niPGT) by comparing the karyotype concordance with corresponding inner cell mass (ICM) among initial trophectoderm (TE) biopsy, TE re-biopsy, and BCM sampling.

Design

Re-analysis aneuploid/mosaic blastocysts donated for research by couples.

Setting

Institutional in vitro fertilization center.

Patient(s)

A total of 12 couples donated their blastocysts, which had previously been diagnosed as aneuploid or mosaic by initial TE-biopsy preimplantation genetic testing for aneuploidy (PGT-A) for research.

Intervention(s)

A total of 26 frozen−thawed blastocysts were re-analyzed by TE re-biopsy, ICM biopsy, and the collection of spent BCM.

Main Outcome Measure(s)

Karyotype concordance rates.

Result(s)

For 23 embryos diagnosed as aneuploid by initial TE biopsy, 78.3% of initial TE samples, 87.0% of TE re-biopsies samples, and 78.3% of BCM samples were concordant with corresponding ICM samples, and for three mosaic embryos, the concordance rates with ICM of these three groups were 0%, 100%, and 100%, respectively. With the corresponding ICM result as the true result, sensitivity of both niPGT-A and initial TE were 100%; however, the false-positive rate (FPR) of initial TE was higher than that of niPGT-A (100% vs. 0).

Conclusion(s)

niPGT-A using BCM had diagnostic efficiency similar to that of TE-biopsy PGT-A. In the case of mosaic embryos, niPGT-A using BCM may be more reliable for predicting karyotypes of ICM than initial TE biopsy.

Non-invasive preimplantation genetic testing (niPGT): the next revolution in reproductive genetics?

BACKGROUND

Preimplantation genetic testing (PGT) encompasses methods that allow embryos to be tested for severe inherited conditions or for chromosome abnormalities, relevant to embryo health and viability. In order to obtain embryonic genetic material for analysis, a biopsy is required, involving the removal of one or more cells. This invasive procedure greatly increases the costs of PGT and there have been concerns that embryo viability could be compromised in some cases. The recent discovery of DNA within the blastocoele fluid (BF) of blastocysts and in spent embryo culture media (SCM) has led to interest in the development of non-invasive methods of PGT (niPGT).

OBJECTIVE AND RATIONALE

This review evaluates the current scientific evidence regarding non-invasive genetic assessment of preimplantation embryos. The success of different PGT methodologies in collecting and analysing extra-embryonic DNA is evaluated, and consideration is given to the potential biological and technical hindrances to obtaining a reliable clinical diagnosis.

SEARCH METHODS

Original research and review papers concerning niPGT were sourced by searching PubMed and Google Scholar databases until July 2019. Searches comprised the keywords: 'non-invasive'; 'cell-free DNA'; 'blastocentesis'; 'blastocoel fluid'; 'spent culture media'; 'embryo culture medium'; 'preimplantation genetic testing'; 'preimplantation genetic diagnosis'; 'preimplantation genetic screening'; and 'aneuploidy'.

OUTCOMES

Embryonic DNA is frequently detectable in BF and SCM of embryos produced during IVF treatment. Initial studies have achieved some success when performing cytogenetic and molecular genetic analysis. However, in many cases, the efficiency has been restricted by technical complications associated with the low quantity and quality of the DNA. Reported levels of ploidy agreement between SCM/BF samples and biopsied embryonic cells vary widely. In some cases, a discrepancy with respect to cytogenetic data obtained after trophectoderm biopsy may be attributable to embryonic mosaicism or DNA contamination (usually of maternal origin). Some research indicates that aneuploid cells are preferentially eliminated from the embryo, suggesting that their DNA might be over-represented in SCM and BF samples; this hypothesis requires further investigation.

WIDER IMPLICATIONS

Available data suggest that BF and SCM samples frequently provide DNA templates suitable for genetic analyses, offering a potential means of PGT that is less expensive than traditional methods, requires less micromanipulation skill and poses a lower risk to embryos. Critically, DNA isolation and amplification protocols must be optimised to reproducibly obtain an accurate clinical diagnosis, whilst minimising the impact of confounding factors such as contamination. Further investigations are required to understand the mechanisms underlying the release of embryonic DNA and to determine the extent to which this material reflects the true genetic status of the corresponding embryo. Currently, the clinic al potential of niPGT remains unknown.

A blastocyst biopsy approach for preimplantation genetic diagnosis technique that affects the expression of SNAP-α in mice

Preimplantation genetic diagnosis (PGD) is a technique that is commonly used during assisted reproduction in the clinics to eliminate genetically abnormal embryos before implantation. The blastomere biopsy technique has risks related to the embryo, but blastocyst biopsy has not been systematically evaluated in relation to effects after birth, and the resulting offspring have not been followed up on. We designed a series of experiments to evaluate the risk of blastocyst biopsy on the resulting progeny. Mice were divided into a PGD group and a control group. The former was the progeny of mice that underwent blastocyst biopsy and the latter was delivered through a normal pregnancy without blastocyst biopsy. Each group consisted of 15 animals. We found no effects of blastocyst biopsy on reproductive capacities and weight gain. As for neurobehavioral evaluation between both groups, there were no significant differences in tail suspension test, sucrose preference test, the open field test and the elevated plus maze. Western blotting, immunohistochemistry and quantitative RT-PCR results showed that the expression levels of MBP, PRDX5 and UCHL1 in the PGD group were not significantly different compared to the control group, but SNAP-α expression in the PGD group was lower than that in control group. In summary, we concluded that blastocyst biopsy had no adverse effect on the general growth and behavior in mice. However, blastocyst biopsy effected the expression of SNAP-α. Therefore, the safety of blastocyst biopsy requires further evaluation.

The enigmatic morula: mechanisms of development, cell fate determination, self-correction and implications for ART

BACKGROUND

Assisted reproduction technology offers the opportunity to observe the very early stages of human development. However, due to practical constraints, for decades morphological examination of embryo development has been undertaken at a few isolated time points at the stages of fertilisation (Day 1), cleavage (Day 2-3) and blastocyst (Day 5-6). Rather surprisingly, the morula stage (Day 3-4) has been so far neglected, despite its involvement in crucial cellular processes and developmental decisions.

OBJECTIVE AND RATIONALE

The objective of this review is to collate novel and unsuspected insights into developmental processes occurring during formation of the morula, highlighting the key importance of this stage for a better understanding of preimplantation development and an improvement of ART.

SEARCH METHODS

PubMed was used to search the MEDLINE database for peer-reviewed English-language original articles and reviews concerning the morula stage in mammals. Searches were performed by adopting 'embryo', 'morula', 'compaction', 'cell fate' and 'IVF/assisted reproduction' as main terms, in association with other keywords expressing concepts relevant to the subject (e.g. cell polarity). The most relevant publications, i.e. those concerning major phenomena occurring during formation of the morula in established experimental models and the human species, were assessed and discussed critically.

OUTCOMES

Novel live cell imaging technologies and cell biology studies have extended our understanding of morula formation as a key stage for the development of the blastocyst and determination of the inner cell mass (ICM) and the trophectoderm (TE). Cellular processes, such as dynamic formation of filopodia and cytoskeleton-mediated zippering cell-to-cell interactions, intervene to allow cell compaction (a geometrical requisite essential for development) and formation of the blastocoel, respectively. At the same time, differential orientation of cleavage planes, cell polarity and cortical tensile forces interact and cooperate to position blastomeres either internally or externally, thereby influencing their cellular fate. Recent time lapse microscopy (TLM) observations also suggest that in the human the process of compaction may represent an important checkpoint for embryo viability, through which chromosomally abnormal blastomeres are sensed and eliminated by the embryo.

WIDER IMPLICATIONS

In clinical embryology, the morula stage has been always perceived as a 'black box' in the continuum of preimplantation development. This has dictated its virtual exclusion from mainstream ART procedures. Recent findings described in this review indicate that the morula, and the associated process of compaction, as a crucial stage not only for the formation of the blastocyst, but also for the health of the conceptus. This understanding may open new avenues for innovative approaches to embryo manipulation, assessment and treatment.

Morphokinetic characteristics of embryos originating from extremely small follicles: A prospective study

OBJECTIVE

To investigate the developmental potential of oocytes and embryos derived from extremely small follicles (<10 mm) in comparison to those originated in larger follicles.

STUDY DESIGN

A prospective study, undertaken in a university affiliated single center tertiary hospital. The study included 98 patients undergoing infertility treatments. On the day of ovum pickup (OPU) follicles were counted and measured. Aspiration of follicles larger and smaller than 10 mm was undertaken separately and the development of embryos originating from oocytes from these follicles was followed up using different wells for each embryo. There was no low limit of size for aspiration. Each oocyte retrieved was marked for its origin and numbered for further follow up. We recorded: Oocytes retrieved, maturation stage, fertilization rate, cleavage rate, morphokinetic parameters, embryo transfers, embryo freezing, oocyte freezing and biopsy rate for preimplantation genetic diagnosis (PGD). Quality was evaluated by the morphokinetic parameters of the embryos developed using time-lapse imaging technology. Day 3 KIDScore was calculated to all embryos.

RESULTS

Small follicles compared to large follicles displayed lower recovery rate (45% vs. 74%, P < 0.0001), fewer matured oocytes (37.5% vs. 61.7%, P < 0.0001), higher rates of GV oocytes (20.7% vs., 3.7%, P < 0.0001), and lower fertilization rate (43.7% vs. 63.3%, P < 0.0001. However, morphokinetic variables were similar between embryos that originated from either small or large follicles. Median KIDscores were identical for embryos from small or large follicle origin.

CONCLUSIONS

Embryos originated from small follicles were not different than embryos from larger follicles, as assessed by morphokinetic parameters in time lapse system. In view of our findings, physicians should bear in mind that small follicle aspiration might yield good quality embryos.

Optimal timing for blastomere biopsy of 8-cell embryos for preimplantation genetic diagnosis

STUDY QUESTION

What is the optimal timing for blastomere biopsy during the 8-cell stage, at which embryos will have the best implantation potential?

SUMMARY ANSWER

Fast-cleaving embryos that are biopsied during the last quarter (Q4) of the 8-cell stage and are less affected by the biopsy procedure, and their implantation potential is better than that of embryos biopsied earlier during the 8-cell stage (Q1-Q3).

WHAT IS KNOWN ALREADY

Blastomer biopsy from cleavage-stage embryos is usually performed on the morning of Day 3 when the embryos are at the 6- to 8-cell stage and is still the preferred biopsy method for preimplantation genetic diagnosis (PGD) for monogentic disorders or chromosomal translocations. Human embryos usually remain at the 8-cell stage for a relatively long 'arrest phase' in which cells grow, duplicate their DNA and synthesize various proteins in preparation for the subsequent division.

STUDY DESIGN, SIZE, DURATION

This is a retrospective cohort study. The study group (195 embryos) included all 8-cell stage embryos that underwent blastomere biopsy for PGD for monogenetic disorders and chromosomal translocations in our unit between 2012-2014 and cultured in the EmbryoScope until transfer. The control group (115 embryos) included all embryos that underwent intracytoplasmic sperm injection without a biopsy during the same period.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The 8-cell stage was divided into four quarters: the first 5 h post-t8 (Q1), 5-10 h post-t8 (Q2), 10-15 h post-t8 (Q3) and at 15-20 h post-t8 (Q4). Non-biopsied control embryos were divided into four equivalent quarters. Embryos were evaluated for timing of developmental events following biopsy including timing of first cleavge after biopsy, timing of comapction (tM) and start of blastulation (tSB). Timing of these events were compared between PGD and control embryos, as well as with 56 PGD implanted embryos with Known Implantation Data (PGD-KID-positive embryos).

MAIN RESULTS AND THE ROLE OF CHANCE

Embryos that were biopsied during Q3 (10-15 h from entry into 8-cell stage) were delayed in all three subsequent developmental events, including first cleavage after biopsy, compaction and start of blastulation. In contrast, these events occurred exactly at the same time as in the control group, in embryos that were biopsied during Q1, Q2 or Q4 of the 8-cell stage. The results show also that embryos that were biopsied during Q1, Q2 or Q3 of the 8-cell stage demonstrated a significant delay from the biopsied implanted embryos already in t8 as well as in tM and tSB. However, embryos that were biopsied during Q4 demonstrated dynamics similar to those of the biopsied implanted embryos in t8 and tM, and a delay was noticed only in the last stage of tSB.

LIMITATIONS, REASONS FOR CAUTION

This is a retrospective study that is limited to the timing of biopsy that is routinely performed in the IVF lab. A prospective study in which biopsy will be performed at a desired timing is needed in order to differ between the effect of biopsy itself and the cleavage rate of the embryo.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings showed that blastomere biopsy can be less harmful to further development if it is carried out during a critical period of embryonic growth, i.e during Q4 of the 8-cell stage. They also demonstrated the added value of time-lapse microscopy for determining the optimal timing for blastomere biopsy.

STUDY FUNDING/COMPETING INTEREST(S)

The study was funded by the routine budget of our IVF unit.

TRIAL REGISTRATION NUMBER

N/A.

Time-lapse imaging reveals delayed development of embryos carrying unbalanced chromosomal translocations

PURPOSE

The purpose of the study was to compare the morphokinetic parameters of embryos carrying balanced chromosomal translocations with those carrying unbalanced chromosomal translocations using time-lapse microscopy.

METHODS

The study group included 270 embryos that underwent biopsies on day 3 for preimplantation genetic diagnosis (PGD) for chromosomal translocations in our unit between 2013 and 2015. All embryos were incubated under time-lapse microscopy and evaluated for timing of developmental events up to day 5. The timing of these events was compared between balanced and unbalanced embryos, potentially viable and nonviable variants, and maternal versus paternal inheritance of the translocation.

RESULTS

The PGD analysis found that 209 (77%) of the 270 biopsied embryos carried an unbalanced translocation. Embryos carrying unbalanced translocations, which are expected to lead to implantation failure or miscarriage, cleaved less synchronously and were delayed in time of cleavage to the 4-cell stage (t4) and in time of start of blastulation (tSB) compared with balanced embryos (P < 0.05). Furthermore, embryos carrying nonviable translocations demonstrated a significant delay at the time of pronuclei fading (tPNf) compared with those carrying potentially viable translocations (P < 0.05). Embryos whose unbalanced translocations were of maternal origin were significantly delayed in most of the morphokinetic parameters (including tPNf, t2, t3, t4, t6, t7, t8, cc2, s2, and tSB) compared with embryos carrying balanced translocations (P < 0.05).

CONCLUSIONS

Embryos carrying unbalanced chromosomal translocations mainly of maternal origin undergo delayed development and asynchronous cleavage that may lead to implantation failure or miscarriage.

Impact of polar body biopsy on embryo morphokinetics-back to the roots in preimplantation genetic testing?

Purpose

Polar body biopsy (PBB) is a common technique in preimplantation genetic testing (PGT) to assess the chromosomal status of the oocyte. Numerous studies have been implemented to investigate the impact of biopsies on embryo development; however, information on embryo morphokinetics is still lacking. Hence, we investigated the impact of PBB on morphokinetic parameters in early embryo development.

Methods

Four hundred four embryos (202 PBB, 202 control) were retrospectively analyzed. Patients were stimulated with a gonadotropin-releasing hormone antagonist ovarian hyperstimulation protocol. After fertilization check, embryos were incubated in a time-lapse incubator. The groups were matched for maternal age at time of oocyte retrieval.

Results

Mean group times for reaching specific developmental time points showed no significant difference comparing embryos with PBB conducted and without. Likewise, further subdivision of the PBB group in euploid and aneuploid embryos revealed no differences in the early embryo morphokinetic development compared to the control group. Aneuploidy testing revealed a high prevalence of chromosomal aberrations for chromosomes 21, 4, 16, and 19.

Conclusions

In conclusion, PBB does not impact the morphokinetic parameters of the embryo development. PBB can be safely applied without the risk of impairing the reproductive potential of the embryo and can be highly recommended as safe and practicable PGT approach, especially in countries with prevailing restrictions regarding PGT analysis.

High-efficiency derivation of human embryonic stem cell lines using a culture system with minimized trophoblast cell proliferation

Background

Due to their extensive self-renewal and multilineage differentiation capacity, human embryonic stem cells (hESCs) have great potential for studying developmental biology, disease modeling, and developing cell replacement therapy. The first hESC line was generated in 1998 by culturing inner cell mass (ICM) cells isolated from human blastocysts using an immunosurgery technique. Since then, many techniques including mechanical ICM isolation, laser dissection, and whole embryo culture have been used to derive hESC lines. However, the hESC derivation efficiency remains low, usually less than 50%, and it requires a large number of human embryos to derive a significant number of hESC lines. Due to a shortage of and restricted access to human embryos, a novel approach with better hESC derivation efficiency is badly needed to decrease the number of embryos used.

Methods

We hypothesized that the low hESC derivation efficiency might be due to extensive proliferation of trophoblast (TE) cells which could interfere with ICM proliferation. We therefore developed a methodology to minimize TE cell proliferation by culturing ICM in a feeder-free system for 3 days before transferring them onto feeder cells.

Results

This minimized trophoblast cell proliferation (MTP) technique could be successfully used to derive hESCs from normal, abnormal, and frozen–thawed embryos with better derivation efficiency of more than 50% (range 50–100%; median 70%).

Conclusions

We successfully developed a better hESC derivation methodology using the “MTP” culture system. This methodology can be effectively used to derive hESCs from both normal and abnormal embryos under feeder-free conditions with higher efficiency when compared with other methodologies. With this methodology, large-scale production of clinical-grade hESCs is feasible.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0866-5) contains supplementary material, which is available to authorized users.

Embryo biopsy and development: the known and the unknown

Preimplantation genetic diagnosis (PGD) has been introduced in clinical practice as a tool for selecting ‘healthy’ embryos before their transfer in utero. PGD protocols include biopsy of cleaving embryos (blastomere biopsy (BB)) or blastocysts (trophectoderm biopsy (TB)), followed by genetic analysis to select ‘healthy’ embryos for transfer in utero. Currently, TB is replacing the use of BB in the clinical practice. However, based on the European Society of Human Reproduction and Embryology Preimplantation Genetic Diagnosis Consortium reports, BB has been used in >87% of PGD cycles for more than 10 years. An exhaustive evaluation of embryo biopsy (both BB and TB) risks and safety is still missing. The few epidemiological studies available are quite controversial and/or are limited to normalcy at birth or early childhood. On the other hand, studies on animals have shown that BB can be a risk factor for impaired development, during both pre- and postnatal life, while little is known on TB. Thus, there is an urgent need of focused researches on BB, as it has contributed to give birth to children for more than 10 years, and on TB, as its application is significantly growing in clinical practice. In this context, the aim of this review is to provide a complete overview of the current knowledge on the short-, medium- and long-term effects of embryo biopsy in the mouse model.