Prevention of age-related aneuploidies by polar body testing of oocytes

Sperm and Oocyte Chromosomal Abnormalities

Gametogenesis, the process of producing gametes, differs significantly between oocytes and sperm. Most oocytes have chromosomal aneuploidies, indicating that chromosomal aberrations in miscarried and newborn infants are of oocyte origin. Conversely, most structural anomalies are of sperm origin. A prolonged meiotic period caused by increasing female age is responsible for an increased number of chromosomal aberrations. Sperm chromosomes are difficult to analyze because they cannot be evaluated using somatic cell chromosome analysis methods. Nevertheless, researchers have developed methods for chromosome analysis of sperm using the fluorescence in situ hybridization method, hamster eggs, and mouse eggs, allowing for the cytogenetic evaluation of individual sperm. Reproductive medicine has allowed men with severe spermatogenic defects or chromosomal abnormalities to have children. However, using these techniques to achieve successful pregnancies results in higher rates of miscarriages and embryos with chromosomal abnormalities. This raises questions regarding which cases should undergo sperm chromosome analysis and how the results should be interpreted. Here, we reviewed clinical trials that have been reported on oocyte and sperm chromosome analyses. Examination of chromosomal abnormalities in gametes is critical in assisted reproductive technology. Therefore, it is necessary to continue to study the mechanism underlying gametic chromosomal abnormalities.

Assessment of the relationship of basal serum anti-mullerian hormone levels with oocyte quality and pregnancy outcomes in patients undergoing ICSI

BACKGROUND

Anti-Mullerian hormone (AMH) is constantly secreted during menstrual cycles and may offer several advantages over traditional biomarkers of ovarian reserve.

OBJECTIVE

To assess the relationship of anti-Mullerian hormone (AMH) values, which are used to evaluate ovary reserves, with oocyte and embryo quality and with ART outcomes in patients undergoing intra-cytoplasmic sperm injection (ICSI).

MATERIALS AND METHODS

This cross sectional study was performed using 50 women undergoing ICSI in IVF center of Zeynep Kamil Women's and Children's Hospital, İstanbul, Turkey. All patients received the long protocol. Follicle-stimulating hormone, luteinizing hormone, estradiol, and AMH levels were measured and antral follicle counts were obtained on the 3(rd) day of menstruation. A cut-off value based on the number of oocytes was determined for AMH, and women were evaluated after being divided into two groups as bad responders and good responders, according to their AMH levels.

RESULTS

Twelve (27.3%) women were in bad responders group and 32 (72.7%) women were in good responders group. AMH measurements were statistically significantly different between the two groups (p<0.01). Based on this significance, the researchers used ROC analysis to estimate a cut-off point for AMH. The researchers detected the good responders with an AMH level 1.90 or above, with 87.50% sensitivity, 66.67% specificity, 87.50% positive prediction, and 66.67% negative prediction (AUC=0.777, p<0.01).

CONCLUSION

Basal AMH levels can be used as an indicator to determine the ovarian response in women undergoing ICSI. AMH can be used to predict the number of mature oocytes that can be collected during treatment and the number of oocytes that can be fertilized. However, AMH is not a valuable tool to evaluate oocyte quality, the development of high-quality embryos, or pregnancy conception.

Preimplantation Genetic Diagnosis: Prenatal Testing for Embryos Finally Achieving Its Potential

Preimplantation genetic diagnosis was developed nearly a quarter-century ago as an alternative form of prenatal diagnosis that is carried out on embryos. Initially offered for diagnosis in couples at-risk for single gene genetic disorders, such as cystic fibrosis, spinal muscular atrophy and Huntington disease, preimplantation genetic diagnosis (PGD) has most frequently been employed in assisted reproduction for detection of chromosome aneuploidy from advancing maternal age or structural chromosome rearrangements. Major improvements have been seen in PGD analysis with movement away from older, less effective technologies, such as fluorescence in situ hybridization (FISH), to newer molecular tools, such as DNA microarrays and next generation sequencing. Improved results have also started to be seen with decreasing use of Day 3 blastomere biopsy in favor of polar body or Day 5 trophectoderm biopsy. Discussions regarding the scientific, ethical, legal and social issues surrounding the use of sequence data from embryo biopsy have begun and must continue to avoid concern regarding eugenic or inappropriate use of this technology.

Anti-Müllerian hormone (AMH): a reliable biomarker of oocyte quality in IVF

PURPOSE

To evaluate the impact of serum AMH levels on stimulated IVF implantation and clinical pregnancy rates.

METHODS

•

DESIGN

Retrospective study with multivariate analysis. •

SETTING

Clinique ovo (Montreal University affiliated Center). •

PATIENT(S)

Six hundred and thirty seven patients undergoing a stimulated IVF protocol were included. Only non-polycystic ovary patients at their first IVF attempt were considered for the analysis. •

INTERVENTION(S)

None. •

MAIN OUTCOME MEASURES(S)

Implantation and ongoing pregnancy rates.

RESULT(S)

Cycle outcomes were analysed according to AMH percentiles based on the AMH normogram per patient's age of our infertile population. Multivariate analyses were done to adjust for potential confounding factors such as age, total exogenous FSH dosage and number of eggs retrieved. Compared to the reference population, a significant lower mean implantation rate (0.26 vs 0.45) was observed in patients under 35 years of age with AMH < 1 ng/ml. Women with AMH < 25th percentile had less chances of having an embryo transferred, lower chances of having an ongoing pregnancy per started IVF cycle and a lower embryo freezing rate compared to the reference population.

CONCLUSION(S)

Patients with AMH < 0.47 ng/ml should be advised before starting a stimulated IVF cycle of the poorer prognosis compared to our reference population independently of their age, total exogenous FSH dosage and number of eggs retrieved. Therefore, AMH could enable a more individualized number of embryo transfer policy based on oocyte quality.

A study of meiotic segregation in a fertile human population following ovarian stimulation with recombinant FSH-LH

OBJECTIVE

The aim of the study is to investigate the meiotic segregation in fresh eggs from anonymous egg donors and to analyze the baseline levels of aneuploidy in this population.

RESULTS

The study includes the largest series of donor eggs so far studied: 203 eggs from donors aged between 20 and 31 years. No diagnosis was obtained in 10.8 % of cases (22/ 203). The biopsy of the first and second polar bodies was completed in a sequential manner on day 0 and day 1 of embryo development. Chromosomes 13, 16, 18, 21 and 22 are analyzed by means of the FISH test. The diagnosable fertilized eggs gave an aneuploidy rate of 19.1 % (31/162), with 83.8 % (26/31) of the errors produced during meiosis I, 12.9 % (4/31) produced during meiosis II, and 3.2 % (1/31) produced during both meiosis I and II. The premature division of sister chromatids is the main source of meiotic error during Meiosis I, resulting in the creation of oocyte aneuploidy.

CONCLUSIONS

FISH analysis of the first and second polar body in donor oocytes gave an aneuploidy rate of 19.1 %. This study shows the majority of errors occur during Meiosis I.

Follicular fluid protein content (FSH, LH, PG4, E2 and AMH) and polar body aneuploidy

PURPOSE

Our objective was to identify a marker for oocyte aneuploidy in follicular fluid (FF) in women with an increased risk of oocyte aneuploidy after controlled ovarian hyperstimulation.

MATERIALS AND METHODS

Three groups of oocytes were constituted for polar body screening by FISH (chromosomes 13, 16, 18, 21 and 22): Group 1, advanced maternal age (n = 156); Group 2, implantation failure (i.e. no pregnancy after the transfer of more than 10 embryos; n = 101) and Group 3, implantation failure and advanced maternal age (n = 56). FSH and other proteins were assayed in the corresponding FF samples.

RESULTS

Of the 313 oocytes assessed, 35.78 % were abnormal. We found a significant difference between the follicular FSH levels in normal oocytes and abnormal oocytes (4.85 ± 1.75 IU/L vs. 5.41 ± 2.47 IU/L, respectively; p = 0.021). We found that the greater the number of chromosomal abnormalities per oocyte (between 0 and 3), the higher the follicular FSH level.

CONCLUSION

High FF FSH levels were associated with oocyte aneuploidy in women having undergone controlled ovarian hyperstimulation.

Predicting aneuploidy in human oocytes: key factors which affect the meiotic process

BACKGROUND

To estimate the incidence of aneuploidy in relation to patients' characteristics, the type of hormonal stimulation and their response to induction of multiple follicular growth, 4163 first polar bodies (PB1s) were analyzed.

METHODS

Five hundred and forty four infertile couples underwent 706 assisted conception cycles (640 with poor prognosis indications and 66 controls) in which chromosomal analysis of PB1 for the chromosomes 13, 15, 16, 18, 21 and 22 was performed. Results were evaluated in a multivariate analysis.

RESULTS

The proportion of normal oocytes was directly correlated (P < 0.01) with (i) the number of mature oocytes and (ii) the establishment of a clinical pregnancy; and inversely correlated (P < 0.01) with (i) female age, (ii) causes of female infertility (endometriosis, abortions, ovulatory factor), (iii) poor prognosis indications (female age, number of previous cycles, multiple poor prognosis indications), (iv) number of FSH units per oocyte and (v) number of FSH units per metaphase II oocyte. There was a weak significance of frequency (P < 0.05) between type of abnormality (originated by chromatid predivision, chromosome non-disjunction or combined mechanisms in the same oocyte) and groups of the studied variables, rather than to a specific abnormality or a specific chromosome.

CONCLUSIONS

The type of infertility had a significant effect on errors derived from the first meiotic division, whose incidence was significantly higher in the presence of endometriosis or of an ovulatory factor, and in women that experienced repeated abortions. Each aneuploidy event was found to be dependent not on a specific variable, but on groups of variables. In addition, the tendency of chromosomal abnormalities to occur simultaneously implies that the deriving aneuploidies can be of any type.

Accurate single cell 24 chromosome aneuploidy screening using whole genome amplification and single nucleotide polymorphism microarrays

OBJECTIVE

To develop and validate a whole genome amplification and single nucleotide polymorphism (SNP) microarray protocol for accurate single cell 24 chromosome aneuploidy screening.

DESIGN

Prospective, randomized, and blinded study.

SETTING

Academic reproductive medicine center.

PATIENT(S)

Multiple euploid and aneuploid cell lines were obtained from a public repository and blastomeres were obtained after biopsy of cleavage stage embryos from 78 patients undergoing IVF.

MAIN OUTCOME MEASURE(S)

Accuracy of copy number assignment and consistency of individual SNPs, whole chromosomes, and single cell aneuploidy status were determined.

INTERVENTION(S)

None.

RESULT(S)

Single cells extracted from karyotypically defined cell lines provided 99.2% accuracy for individual SNPs, 99.8% accuracy for whole chromosomes, and 98.6% accuracy when applying a quality control threshold for the overall assignment of aneuploidy status. The concurrence for more than 80 million SNPs in 335 single blastomeres was 96.5%.

CONCLUSION(S)

We have established and validated a SNP microarray-based single cell aneuploidy screening technology. Clinical validation studies are underway to determine the predictive value of this methodology.

Spindle and chromosome configurations of human oocytes matured in vitro in two different culture media

In-vitro maturation can have deleterious effects on spindle formation and proper chromosome alignment in human oocytes and can be profoundly affected by culture conditions. This study compared the spindle presence and location with the maturation rate of germinal vesicle (GV) oocytes cultured in two different media: G1.2 and G1.2 supplemented with follicle-stimulating hormone, human chorionic gonadotrophin and 17beta-oestradiol. A total of 304 oocytes were retrieved from 101 women undergoing IVF treatment with intracytoplasmic sperm injection. Spindle presence was recorded using the Polscope. Spindle morphology was evaluated with immunocytological staining for alpha-tubulin and chromatin. Twenty-one in-vitro matured oocytes with the presence of spindle and ten of their corresponding polar bodies (PB) were also assessed for aneuploidy. A significantly increased maturation rate (69.7%) was observed after 24h in the supplemented culture media compared with the G1.2 media (56.6%; P<0.05). The proportions of metaphase II (MII) oocytes with spindle presence and abnormal spindle morphology were similar in the two culture media. Also, 76.9% of MII and 70% of PB had chromosomal abnormalities. In conclusion, supplementing culture media may increase the oocyte maturation rate in vitro, but does not necessarily indicate the presence of a birefringent spindle, or normal spindle and chromosomal alignment.

Quality management system in PGD/PGS: now is the time

PURPOSE

Governments and international authorities require an accreditation of the PGD/PGS laboratories in order to ensure the safety and reproducibility of these analytical procedures. The implementation of a Quality Management System is the first mandatory step prior to accreditation. Our aim is to offer a detailed guidance to the PGD/PGS community that would like to implement this system in the future.

METHODS

The certification was based on the norm ISO 9001:2000 and requires the identification of procedures, definition of the flowchart, documentation of the processes, recognition of the critical control points, establishment of quality controls, performance of validation and audit system.

RESULTS

The achievement of ISO certification with the specific scope of "preimplantation genetic diagnosis".

CONCLUSION

Certification of PGD/PGS allows to achieve evaluation of the efficiency to ensure the sensitivity and a continuous improvement of the genetic diagnosis of embryonic single cells.

Gamete cytogenetic study in couples with implantation failure: aneuploidy rate is increased in both couple members

PURPOSE

Implantation failure is known to be associated with an increased risk of aneuploidy in embryos, a situation leading to a pre-implantation genetic screening, not allowed in different countries like France. Our aim was to evaluate the gamete aneuploidy incidence in this context, using first polar body and spermatozoa aneuploidy screening.

METHODS

Three groups were considered: 11 couples with pregnancy obtained after IVF for female infertility (group 1); 20 couples with pregnancy obtained after IVF for male infertility (group 2); and 35 couples with implantation failure (group 3). In group 3, 28 couples treated by ICSI volunteered for first polar body analysis (PB1).

RESULTS

Spermatozoa aneuploidy rate was increased in groups 2 (1.6%) and 3 (2.1%) in comparison to group 1 (0.6%). PB1 aneuploidy rate was 35.4% in group 3. Finally, eight couples (32%) had no particular chromosomal risk in gametes, 15/25 (60%) presented an increased spermatic (>2%) or oocyte (>1/3) aneuploidy rate, and 2/25 (8%) had both.

CONCLUSION

Those results confirm that implantation failure has a heterogeneous origin, that gamete chromosome abnormality rate is one of the major contributing factors, and that 1st Polar body and spermatozoa aneuploidy screening or pre-implantation genetics screening may be indicated for these couples.

Preimplantation genetic screening: "established" and ready for prime time?

Unless attempts to improve pregnancy rates and/or diminish miscarriage rates through preimplantation genetic screening (PGS) are applied to only carefully selected patients, they will fail. Because specific PGS indications have remained undefined, PGS should be considered an experimental procedure.

Oocyte aneuploidy mechanisms are different in two situations of increased chromosomal risk: older patients and patients with recurrent implantation failure after in vitro fertilization

OBJECTIVE

To clarify the mechanisms underlying oocyte abnormalities in meiosis: meiotic nondisjunction of a whole chromosome or premature separation of sister chromatids in two situations of increased chromosomal risk.

DESIGN

Preconception diagnosis by first polar-body analysis in two situations of increased chromosomal risk.

SETTING

Departments of reproductive biology, cytogenetics, gynecology, and obstetrics.

PATIENT(S)

First polar body analysis was proposed to 76 patients (91 cycles) for advanced age (AMA; n = 30, 36 cycles), recurrent implantation failure (RIF; >10 embryos transferred without implantation; n = 32, 36 cycles), or both (AMA + RIF; n = 14, 19 cycles), before their intracytoplasmic sperm injection procedure.

INTERVENTION(S)

First polar-body analysis using fluorescence in situ hybridization.

MAIN OUTCOME MEASURE(S)

Mechanisms and frequency of aneuploidy.

RESULT(S)

Three hundred eighty-four oocytes were analyzed by fluorescence in situ hybridization, 130 from women >38 years of age, 171 from women with RIF, and 83 from women with both indications. The oocyte abnormality rate was similar in the three groups, respectively, 38.5%, 40.4%, and 45.8%. The aneuploidy mechanisms were different for women >38 years of age who had no previous implantation failure (AMA) compared with women of whatever age who had implantation failure (P<.05 vs. RIF; P<.001 vs. AMA+RIF), with, respectively, for the AMA, RIF, and AMA+RIF groups, 72.2%, 56.6%, and 49.2% premature separation of sister chromatids and 27.8%, 43.4%, and 50.8% meiotic nondisjunction. In the two implantation-failure groups, we distinguished a subgroup (22% in the RIF group and 33% in AMA+RIF group) of patients with >2/3 abnormal oocytes, suggesting a meiosis alteration.

CONCLUSION(S)

The mechanisms accounting for oocyte aneuploidy differed in the two clinical situations of advanced maternal age and RIF. Advanced maternal-age aneuploidy was linked to a loss of sister chromatid cohesion that led to one single chromatid abnormality, whereas implantation failure is a much more heterogeneous situation.

Gender effects on the incidence of aneuploidy in mammalian germ cells

Aneuploidy occurs in 0.3% of newborns, 4% of stillbirths, and more than 35% of all human spontaneous abortions. Human gametogenesis is uniquely and gender-specific susceptible to errors in chromosome segregation. Overall, between 1% and 4% of sperm and as many as 20% of human oocytes have been estimated by molecular cytogenetic analysis to be aneuploid. Maternal age remains the paramount aetiological factor associated with human aneuploidy. The majority of extra chromosomes in trisomic offspring appears to be of maternal origin resulting from nondisjunction of homologous chromosomes during the first meiotic division. Differences in the recombination patterns between male and female meiosis may partly account for the striking gender- and chromosome-specific differences in the genesis of human aneuploidy, especially in aged oocytes. Nondisjunction of entire chromosomes during meiosis I as well as premature separation of sister chromatids or homologues prior to meiotic anaphase can contribute to aneuploidy. During meiosis, checkpoints at meiotic prophase and the spindle checkpoint at M-phase can induce meiotic arrest and/or cell death in case of disturbances in pairing/recombination or spindle attachment of chromosomes. It has been suggested that gender differences in aneuploidy may result from more permissive checkpoints in females than males. Furthermore, age-related loss of chromosome cohesion in oocytes as a cause of aneuploidy may be female-specific. Comparative data about the susceptibility of human male and female germ cells to aneuploidy-causing chemicals is lacking. Increases of aneuploidy frequency in sperm have been shown after exposure to therapeutic drugs, occupational agents and lifestyle factors. Conversely, data on oocyte aneuploidy caused by exogenous agents is limited because of the small numbers of oocytes available for analysis combined with potential maternal age effects. The vast majority of animal studies on aneuploidy induction in germ cells represent cause and effect data. Specific studies designed to evaluate possible gender differences in induction of germ cell aneuploidy have not been found. However, the comparison of rodent data available from different laboratories suggests that oocytes are more sensitive than male germ cells when exposed to chemicals that effect the meiotic spindle. Only recently, in vitro experiments, analyses of transgenic animals and knockdown of expression of meiotic genes have started to address the molecular mechanisms underlying chromosome missegregation in mammalian germ cells whereby striking differences between genders could be shown. Such information is needed to clarify the extent and the mechanisms of gender effects, including possible differential susceptibility to environmental agents.

First meiosis errors in immature oocytes generated by stimulated cycles

OBJECTIVE

To investigate chromosomal errors detected by first polar body (PB) biopsy in relation to the nuclear maturity of the oocytes.

DESIGN

Retrospective study.

SETTING

Reproductive medicine unit.

PATIENT(S)

Eighty-seven cycles were examined by PB biopsy for aneuploidy. Indications were maternal age >or=38 years (49 cycles), repeated IVF failures (22 cycles), and others (16 cycles).

INTERVENTION(S)

First polar bodies were analyzed for the chromosomes 13, 16, 18, 21, and 22 in both in vivo and in vitro matured oocytes. Euploid oocytes were inseminated by intracytoplasmic sperm injection.

MAIN OUTCOME MEASURE(S)

Chromosomal status of the analyzed oocytes, development after intracytoplasmic sperm injection, pregnancy, and implantation rates.

RESULT(S)

In in vitro matured oocytes, the proportion of chromosomal abnormalities was higher than in in vivo matured oocytes (70% vs. 54%, P<.005), with complex abnormalities being the prevailing defect (62% vs. 40%, P<.001). Conversely, the presence of an extra chromatid or the lack of a chromatid was more frequent in in vivo than in in vitro matured oocytes (55% vs. 34%, P<.001).

CONCLUSION(S)

The low viability of in vitro matured oocytes from stimulated cycles could be related to a significantly higher proportion of chromosomal abnormalities compared with in vivo matured oocytes. Complex abnormalities, involving two or more chromosomes, gave the strongest contribution to the detected increase.

IVF results: optimize not maximize

The desire to improve in vitro fertilization (IVF) results has led clinicians to replace more than 1 embryo in the uterus. As a result, multiple births have increased over the last 2 decades to epidemic proportions, exposing the field of assisted conception to justified criticism. This review aims to ensure that physicians involved in the field of fertility treatment are aware of the risks and complications related to multiple pregnancies, and to explore possible strategies such as blastocyst culture, preimplantation genetic screening, and embryo cryopreservation, which can help to control and reverse the tide of multiple pregnancies without reducing the good success rate that modern IVF treatment enjoys. A brief overview of the respective UK legislative system is also presented.

Frequency and distribution of chromosome abnormalities in human oocytes

It was previously shown that more than half of the human oocytes obtained from IVF patients of advanced reproductive age are aneuploid, due to meiosis I and meiosis II errors. The present paper further confirms that 61.8% of the oocytes tested by fluorescent probes specific for chromosomes 13, 16, 18, 21 and 22 are abnormal, representing predominantly chromatid errors, which are the major source of aneuploidy in the resulting embryos. Almost half of the oocytes with meiosis I errors (49.3%) are prone to sequential meiosis II errors, which may lead to aneuploidy rescue in 30.8% of the cases. Half of the detected aneuploidies (49.8%) are of complex nature with involvement of two or more chromosomes, or the same chromosome in both meiotic divisions. The aneuploidy rates for individual chromosomes are different, with a higher prevalence of chromosome 21 and 22 errors. The origin of aneuploidy for the individual chromosomes is also not random, with chromosome 16 and 22 errors originating more frequently in meiosis II, and chromosome 18, 13 and 21 errors in meiosis I. There is an age dependence not only for the overall frequency of aneuploidies, but also for each chromosome error, aneuploidies originating from meiosis I, meiosis II, and both meiosis I and meiosis II errors, as well as for different types of aneuploidies. The data further suggest the practical relevance of oocyte aneuploidy testing for detection and avoidance from transfer of the embryos deriving from aneuploid oocytes, which should contribute significantly to the pregnancy outcomes of IVF patients of advanced reproduction age.

Evidence of a high proportion of premature unbalanced separation of sister chromatids in the first polar bodies of women of advanced age

BACKGROUND

Maternal ageing is the only aetiological factor unequivocally linked to aneuploidy. Two mechanisms seem to explain these abnormalities in oocytes: non-disjunction and premature unbalanced separation of sister chromatids (PSSC). Previous studies of unfertilized oocytes argue for a major role of PSSC in the aetiology of aneuploidy for women of advanced age, but in vitro ageing of the oocytes could influence the results.

METHODS

Owing to the high prevalence of aneuploidy in women of advanced age, chromosomal screening of the first polar body just before ICSI was offered to women (from 38 years of age) included in an assisted reproduction programme.

RESULTS

Among 141 oocytes from 29 women (mean age 40 years and 2 months), 43 (30.5%) were abnormal. Sixty-five abnormalities were found and PSSC was involved in 80% of cases.

CONCLUSION

These results are in accordance with previous studies and confirm, in 'fresh' oocytes, the major role of PSSC in the aetiology of aneuploidy in women of advanced age.

Strategies and clinical outcome of 250 cycles of Preimplantation Genetic Diagnosis for single gene disorders

BACKGROUND

We report on our experience with preimplantation genetic diagnosis (PGD) for single gene disorders (SGDs), from 1999 to 2004, describing strategies and overall clinical outcome of 250 cycles in 174 couples for 23 different genetic conditions.

METHODS

PGD cycles included 15 for autosomal dominant, 148 for autosomal recessive and 19 for X-linked SGDs. In addition, 68 cycles of PGD for SGDs were performed in combination with HLA matching. The strategy in each case used an initial multiplex PCR, followed by minisequencing to identify the mutation(s) combined with multiplex PCR for closely linked informative markers to increase accuracy. Linkage analysis, using intragenic and/or extragenic polymorphic microsatellite markers, was performed in cases where the disease-causing mutation(s) was unknown or undetectable.

RESULTS

In 250 PGD cycles, a total of 1961 cleavage stage embryos were biopsied. PCR was successful in 3409 out of 3149 (92.4%) biopsied blastomeres and a diagnosis was possible in 1849 (94.3%) embryos. Four hundred and twenty-seven embryos were transferred in 211 cycles, resulting in 71 pregnancies (33.6% per embryo transfer), including 15 biochemical pregnancies, six spontaneous miscarriages, two ectopic pregnancies, which were terminated, and nine pregnancies which are still ongoing. The remaining pregnancies were confirmed to be unaffected and went to term without complications, resulting in the birth of 35 healthy babies.

CONCLUSIONS

Minisequencing for mutation detection combined with multiplex fluorescence PCR for linkage analysis is an efficient, accurate and widely applicable strategy for PGD of SGDs. Our experience provides a further demonstration that PGD is an effective clinical tool and a useful option for many couples with a high risk of transmitting a genetic disease.

Construction and fertilization of reconstituted human oocytes

Construction of artificial gametes may be made possible by transferring somatic cells into enucleated oocytes and inducing chromosomal halving of their nuclei. This study examines the possibility of constructing viable human gametes, and their potential for participation in normal fertilization. Spare germinal vesicle-stage oocytes were donated by consenting patients undergoing intracytoplasmic sperm injection (ICSI). Approximately 62% of in-vitro matured oocytes survived enucleation and subsequent cumulus cell injection. Following micromanipulation and subsequent activation, about 40% of the reconstituted oocytes yielded two pronuclear-like entities. This was not accompanied by extrusion of a polar body, but resulted in the formation of two 'putative haploid' pronuclei. Therefore selective removal of a female pronucleus marker was required to restore a balanced ploidy. Male pronuclei were identified by association with sperm mitochondria. Additional pronuclei were then removed, allowing further cleavage. Zygotes derived were 'putatively haploid' in approximately 38% of cases with a limited number of chromosomes assessed. However, on karyotypic analysis, blastomeres isolated from cleaving embryos showed a chaotic distribution of chromosomes. Oocytes could induce 'putative haploidization' of transplanted somatic cell nuclei independently of donor cell gender. Fertilization of artificial oocytes was followed by embryonic cleavage despite blastocyst development and chromosomal content possibly being compromised.

The occurrence of aneuploidy in human: lessons from the cytogenetic studies of human oocytes

During the last 4 decades, the cytogenetic investigation of human oocytes has never stopped to progress, according to the advents of new technologies. Both karyotyping and molecular cytogenetic studies have been reported to date, providing a large body of data on the incidence and the distribution of chromosomal abnormalities in human female gametes. However, these studies display a great variability in results, which may be essentially attributable to the limitations of these techniques when applied to human oocytes. The most relevant analysis have led to the estimate that 15-20% of human oocytes present chromosome abnormalities, and they have emphasized the implication of both whole chromosome nondisjunction and chromatid separation in the occurrence of aneuploidy in human oocytes. The effect of advanced maternal age on the incidence of aneuploidies in human oocytes has also been clearly evidenced by recent reports based on large sample of oocytes or polar bodies, whereas most of initial studies have failed to confirm any relationship between maternal age and aneuploidy in human oocytes.

Effect of maternal age on the frequency of cytogenetic abnormalities in human oocytes

The cytogenetic investigation of human oocytes was initiated in the Sixties, and for the last four decades, this field of research has never stopped progressing as new technologies appear. Numerous karyotyping studies and molecular cytogenetic studies have been reported to date, providing a large body of data on the incidence and the distribution of chromosomal abnormalities in human female gametes, but also displaying a great variability in results, which may be essentially attributable to the technical limitations of these in situ methods when applied to human oocytes. Essentially, the most relevant analyses have led to the estimate that 15-20% of human oocytes display chromosome abnormalities, and they have emphasized the implication of both whole chromosome nondisjunction and chromatid separation in the occurrence of aneuploidy in human oocytes. The effect of advanced maternal age on the incidence of aneuploidies has also been investigated in human oocytes. Most previous studies have failed to confirm any relationship between maternal age and aneuploidy frequency in human oocytes, whereas the more recent reports based on large samples of oocytes or polar bodies have provided evidence for a direct correlation between increased aneuploidy frequency and advanced maternal age, and have clarified the contribution of the various types of malsegregation in the maternal age-dependent aneuploidies.

Karyotyping of human oocytes by cenM-FISH, a new 24-colour centromere-specific technique

BACKGROUND

Metaphase II (MII) chromosome complements are difficult to karyotype. The objective of this study was to investigate the efficiency and limitations of centromere-specific multiplex fluorescence in situ hybridization (cenM-FISH), a new 24 colour FISH technique using centromere-specific probes, to analyse the whole chromosome complement within human oocytes.

METHODS

Oocytes were donated by 34 patients undergoing ovarian stimulation and IVF. The MII oocytes were analysed by means of cenM-FISH, while the confirmation of results was performed by FISH and/or by analysing the corresponding first polar bodies using comparative genomic hybridization (CGH).

RESULTS

A total of 30 cells, corresponding to 16 oocytes and 14 first polar bodies, were successfully karyotyped by either cenM-FISH or CGH. The incidence of aneuploidy was 25%, and eight out of nine aneuploidy events were confirmed by CGH and FISH.

CONCLUSIONS

We demonstrate here for the first time that the identification of any numerical abnormality in oocytes is feasible using cenM-FISH. Despite the fact that the fixation efficiency remains low, the present results confirm the advantage of analysing the whole set of chromosomes to make an accurate estimation of the aneuploidy rate in human oocytes.

Preimplantation Genetic Diagnosis:

Preimplantation genetic diagnosis (PGD) can provide genetic information on embryos obtained through in vitro fertilization (IVF), allowing implantation of embryos identified as unaffected with a given genetic or chromosomal disorder. With the availability of increasingly sophisticated genetic testing, its use has advanced from the selection of female embryos for the prevention of X-linked genetic diseases to testing for single gene disorders via PCR. Recently, PGD has also been used in the setting of assisted reproductive technology to select for chromosomally normal embryos in an effort to increase the rates of implantation and successful pregnancy. As the number of patients undergoing IVF increases, the indications for its use broadens, and more mutations underlying genetic disorders are identified, PGD is becoming more widespread. As this evolution continues, recognition of the limitations of PGD, as well as ethical concerns regarding use and misuse of this technology, need to be considered by patients, clinicians, and policy makers.

Cytogénétique des ovocytes humains : 40 ans de progrès

Chromosomal abnormalities account for the majority of pre- and post- implantation embryo wastage in humans. Most of these abnormalities result from maternal meiotic errors, which preferentially occur during the first meiotic division. Consequently, the cytogenetic analysis of human oocytes has then been considered as a highly valuable source of data for the investigation of both the occurrence and the origin of chromosomal abnormalities in human. During the last 4 decades, the cytogenetic analysis of human oocytes has never stopped progressing, according to the advents of new technologies. Both karyotyping and molecular cytogenetic studies have been reported to date, providing a large body of data on the incidence and the distribution of chromosomal abnormalities in human female gametes. However, these studies display a great variability in results, which may be essentially attributable to the limitations of these techniques when applied to human oocytes. The most relevant analysis have led to the estimate that 15-20% of human oocytes present chromosome abnormalities, and they have emphasized the implication of both whole chromosome non-disjunction and chromatid separation in the occurrence of aneuploidy in human oocytes. The effect of advanced maternal age on the incidence of aneuploidy in human oocytes has also been clearly evidenced by recent reports based on large sample of oocytes or polar bodies.

Meiotic and mitotic nondisjunction: lessons from preimplantation genetic diagnosis

Direct testing of the outcome of the first and second meiotic divisions has become possible with the introduction of preimplantation genetic diagnosis (PGD) for aneuploidies. Testing of oocytes by fluorescent in situ hybridization (FISH) analysis of the first and second polar bodies showed that more than half of oocytes from the IVF patients aged 35 years and older had chromosomal abnormalities, which originated from errors in meiosis I or meiosis II, or both: 41.9% of oocytes were aneuploid after meiosis I and 37.3% aneuploid after meiosis II, with 29.1% of these oocytes having both meiosis I and meiosis II errors. As a result, one third of oocytes detected as normal after meiosis I contained the meiosis II errors, and two thirds of those with meiosis II errors were already abnormal following meiosis I. Although the rates of chromosomal abnormalities deriving from meiosis I and II were comparable, meiosis I errors predominantly resulted in extra chromosome (chromatid) material in oocytes, in contrast to a random distribution of extra and missing chromatids after meiosis II. The majority of meiosis I abnormalities were represented by chromatid errors, which seem to be the major source of chromosomal abnormalities in the resulting embryos. Approximately one third of aneuploid oocytes deriving from sequential errors in the first and second meiotic divisions resulted in a balanced karyotype, representing a possible phenomenon of "aneuploidy rescue" during the second meiotic division. However, the majority of the embryos resulting from such oocytes appeared to be abnormal for the same or different chromosome(s), or were mosaic, suggesting a possible predisposition of the resulting embryos to further mitotic errors. Although the origin of a high frequency of mosaicism at the cleavage stage is not sufficiently understood, the mosaic embryos may originate from the chromosomally abnormal oocytes, as a result of a "trisomy rescue" mechanism during the first mitotic divisions, which renders polar body FISH analysis to have important clinical value for reliable pre-selection of aneuploidy-free embryos for transfer.

Aneuploidy study of human oocytes first polar body comparative genomic hybridization and metaphase II fluorescence in situ hybridization analysis

BACKGROUND

The object of this study was to determine the mechanisms that produce aneuploidy in oocytes and establish which chromosomes are more prone to aneuploidy.

METHODS

A total of 54 oocytes from 36 women were analysed. The whole chromosome complement of the first polar body (1PB) was analysed by comparative genomic hybridization (CGH), while the corresponding metaphase II (MII) oocyte was analysed by fluorescence in situ hybridization (FISH) to confirm the results.

RESULTS

Matched CGH-FISH results were obtained in 42 1PB-MII doublets, of which 37 (88.1%) showed reciprocal results. The aneuploidy rate was 57.1%. Two-thirds of the aneuploidy events were chromatid abnormalities. Interestingly, the chromosomes more frequently involved in aneuploidy were chromosomes 1, 4 and 22 followed by chromosome 16. In general, small chromosomes (those equal to or smaller in size than chromosome 13) were more prone to aneuploidy (chi2-test, P=0.07); 25% of the aneuploid doublets would have been misdiagnosed as normal using FISH with probes for nine-chromosomes.

CONCLUSIONS

The combination of two different techniques, CGH and FISH, for the study of 1PB and MII allowed the identification and confirmation of any numerical chromosome abnormality, as well as helping to determine the mechanisms involved in the genesis of maternal aneuploidy.

The chromosomal analysis of human oocytes. An overview of established procedures

The cytogenetic survey of mature human oocytes has been and remains a subject of great interest because of the prevalence of aneuploidy of maternal origin in abnormal human conceptuses, and the lack of understanding about the non-disjunction processes in human meiosis. The first attempts to analyse the chromosomal content of human female gametes were made in the early 1970s, and led to limited data because of the paucity of materials and the inadequacy of the procedure used. The years to follow brought a resurgence of interest in this field, because of the development of human IVF techniques which made oocytes unfertilized in vitro available for cytogenetic analysis. Numerous studies have since been performed. However, the difficulties in obtaining good chromosome preparations and of performing accurate chromosome identification have reduced the viability of these studies, resulting in large variations in the reported incidences of chromosomal abnormalities. The further introduction of new procedures for oocyte fixation and the screening of large oocyte samples have allowed more reliable data to be obtained and to identify premature chromatid separation as a major mechanism in aneuploidy occurrence. The last decade has been privileged to witness the adaptation of molecular cytogenetic techniques to human oocytes, and thus various powerful procedures have been tried not only on female gametes, but also on polar bodies, involving sequential and multicolour fluorescent in situ hybridization (FISH) labelling, comparative genomic hybridization (CGH), spectral karyotyping and alternative methods such as primed in situ labelling (PRINS) and peptide nucleic acid (PNA) techniques. A large body of data has been obtained, but these studies also display a great variability in the frequency of abnormalities, which may be essentially attributable to the technical limitations of these in situ methods when applied to human oocytes. However, molecular cytogenetic approaches have also evidenced the co-existence of both whole chromosome non-disjunction and chromatid separation in maternal aneuploidy. In addition, the extension of these techniques to oocyte polar body materials has provided additional data on the mechanism of meiotic malsegregation. Improvements of some of these techniques have already been reported. The further development of new approaches for the in situ analysis of human meiosis will increase the impact of cytogenetic investigation of human oocytes in the understanding of aneuploidy processes in humans.

Genetics of gametes and embryos

Chromosome analysis of oocytes, sperm and embryos has mainly relied on fluorescent in situ hybridisation (FISH) and karyotyping. FISH studies have been performed on sperm from fertile and infertile men as well as men carrying known chromosomal translocations. Molecular DNA analyses has aided in the identification and treatment of men with Y chromosome deletions. In oocytes FISH and karyotyping have identified non-disjunction of univalents and predivision of chromatids. Analysis of the chromosomes from human embryos has shown that a high proportion of embryos are mosaic or chaotic, in addition to embryos beings uniformly and abnormal. FISH and PCR have also been used clinically for preimplantation genetic diagnosis (PGD). For patients at risk of transmitting a specific genetic or chromosomal abnormality, 1-2 blastomeres are biopsied from embryos and specific genes or chromosomes analysed. Normal embryos are then transferred to the uterus.

Preimplantation genetic diagnosis

Preimplantation genetic diagnosis (PGD) was introduced at the beginning of the 1990s as an alternative to prenatal diagnosis, to prevent termination of pregnancy in couples with a high risk for offspring affected by a sex-linked genetic disease. At that time, embryos obtained in vitro were tested to ascertain their sex, and only female embryos were transferred. Since then, techniques for genetic analysis at the single-cell level, involving assessment of first and second polar bodies from oocytes or blastomeres from cleavage-stage embryos, have evolved. Fluorescence in-situ hybridisation (FISH) has been introduced for the analysis of chromosomes and PCR for the analysis of genes in cases of monogenic diseases. In-vitro culture of embryos has also improved through the use of sequential media. Here, we provide an overview of indications for, and techniques used in, PGD, and discuss results obtained with the technique and outcomes of pregnancies. A brief review of new technologies is also included.

Investigation of chromosomal imbalance in human embryos using comparative genomic hybridization

Studies of cleavage-stage human embryos using fluorescence in-situ hybridization (FISH) to identify sub-sets of chromosomes have indicated that the incidence of chromosomal abnormalities is high. Whole genome amplification (WGA) and comparative genomic hybridization (CGH) to investigate the full chromosome complement applied to a small number of human embryos suggested an even higher rate of abnormality. WGA and CGH were used to identify genomic imbalance in individual blastomeres from human embryos, and the results were correlated with FISH analysis of sibling blastomeres. Forty embryos were analysed; 17 (42.5%) had a normal diploid karyotype and 23 (57.5%) were abnormal, with a chromosome imbalance in one or more cells including three (7.5%) that had a chaotic chromosome complement. Of the abnormal embryos, only three showed consistent aneuploidy. FISH results obtained from sibling blastomeres were in agreement with the CGH results in all 22 of the embryos where both tests were informative. It is concluded that rates of meiotic aneuploidy in human embryos may be lower than previous estimates. The results indicate that chromosomally abnormal embryos were more likely to have arisen as a result of cultural artefact or inadequate cell cycle surveillance, rather than meiotic error.

Analysis of nine chromosome probes in first polar bodies and metaphase II oocytes for the detection of aneuploidies

We used fluorescent in situ hybridisation (FISH) to detect nine chromosomes (1, 13, 15, 16, 17, 18, 21, 22 and X) in 89 first Polar Bodies (1PBs), from in vitro matured oocytes discarded from IVF cycles. In 54 1PBs, we also analysed the corresponding oocyte in metaphase II (MII) to confirm the results; the other 35 1PBs were analysed alone as when preimplantation genetic diagnosis using 1PB (PGD-1PB) is performed. The frequency of aneuploid oocytes found was 47.5%; if the risk of aneuploidy for 23 chromosomes is estimated, the percentage rises to 57.2%. Missing chromosomes or chromatids found in 1PBs of 1PB/MII doublets were confirmed by MII results in 74.2%, indicating that only 25.8% of them were artefactual. Abnormalities observed in 1PBs were 55.8% whole-chromosome alterations and 44.2% chromatid anomalies. We observed a balanced predivision of chromatids for all chromosomes analysed. Differences between balanced predivision in 1PB and MII were statistically significant (P&<0.0001, chi(2) test); the 1PB was most affected. The mean abnormal segregation frequency for each chromosome was 0.89% (range 0.52-1.70%); so, each of the 23 chromosomes of an oocyte has a risk of 0.89% to be involved in aneuploidy. No significant differences were observed regarding age, type of abnormality (chromosome or chromatid alterations) or frequency of aneuploidy. Nine of the 35 patients (25.7%) whose 1PB and MII were studied presented abnormalities (extra chromosomes) that probably originated in early oogenesis. Analysis of 1PBs to select euploid oocytes could help patients of advanced age undergoing in vitro fertilization (IVF) treatment.

Methods in preimplantation genetic diagnosis

Preimplantation genetic diagnosis (PGD) is a new strategy, orientated toward primary prevention of congenital anomalies in couples with reproductive risk, such as advanced maternal age, carriers of chromosomal abnormalities, and carriers of monogenic conditions. For these patients, PGD is an acceptable alternative to prenatal diagnosis, mainly in those countries where pregnancy interruption is forbidden by law. PGD effectively avoids the implications linked to traditional prenatal diagnosis. Centres that provide medical servicies on reproductive biomedicine are responsible for the development and improvement of this new prevention strategy. Thanks to advances in micromanipulation techniques, associated with recent progress in molecular genetics, PGD may be employed for any genetic condition in the future.

Chromosomal abnormalities in a series of 6,733 human oocytes in preimplantation diagnosis for age-related aneuploidies

Most chromosomal abnormalities originate from female meiosis and contribute significantly to pregnancy failures, particularly in women of advanced maternal age. A total of 8,382 oocytes were obtained in 1,297 IVF cycles from patients of advanced maternal age (mean 38.5 years). Following a standard IVF protocol, oocytes were tested following removal and fluorescence in-situ hybridization (FISH) analysis of the first (PB1) and second polar bodies (PB2), using probes specific for chromosomes 13, 16, 18, 21 and 22 (Vysis). FISH results were available in 67,33 (80.3%) oocytes tested, 3,509 (52.1%) of which were aneuploid, with the remaining 3,224 (47.9%) normal oocytes available for transfer. In all, 41.7% of oocytes had meiosis I errors, compared to 35.1% with meiosis II errors. Abnormalities in meiosis I were represented by extra chromatids in 15.4%, missing chromatids in 48.1%, missing chromosomes in 5.9%, extra chromosomes in 0.5%, and complex abnormalities in 30.1%. The proportions of abnormal oocytes with missing or extra chromatids in meiosis II were 36.6 and 41.2% respectively, with the remaining oocytes having complex abnormalities, involving missing or extra chromatids of different chromosomes (22.1%) following meiosis II. Overall, 41.8% oocytes had meiosis I, 30.7% meiosis II, and 27.6% both meiotic division errors. A total of 45.1% of the abnormal oocytes had complex errors, involving the same chromosome in both meiotic divisions (21.5%), or different chromosomes (78.5%), of which 74.8% were with abnormalities of two, and 25.2% with abnormalities of three chromosomes studied. Of 3,224 detected aneuploidy-free zygotes, 2,587 were transferred in 1,100 treatment cycles (2.35 embryos per transfer), resulting in 241 (21.9%) clinical pregnancies and 176 healthy children born, suggesting a positive clinical outcome following aneuploidy testing of oocytes in a group of IVF patients of average age 38.5 years.

Chemical pregnancies: immunologic and ultrasonographic studies

PROBLEM

Implantation of the embryo determines successful from unsuccessful cycles after in vitro fertilization (IVF) and embryo transfer (ET). The purpose of this study was to compare immunologic risk factors among women experiencing implanation failure characterized by a negative pregnancy test after IVF/ET and those experiencing chemical pregnancies. In addition ultrasonographic measurement of gestational sac size from 24 to 35 days from last menstrual period (LMP) were compared between chemical pregnancies and other pregnancy outcomes.

METHODS OF STUDY

Blood samples from 122 women experiencing IVF implantation failure with a negative pregnancy test after ET and 20 women with chemical pregnancies were evaluated for the presence of antiphospholipid antibodies (APA), antinuclear antibodies (ANA), circulating embryotoxins (ETA) and elevated levels of natural killer (NK) cells. Gestational sac size measured from 24 to 35 days form LMP were compared according to pregnancy outcome: term birth (n = 46), ectopic pregnancy (n = 49), spontaneous abortion (n = 56) and chemical pregnancy (n = 20).

RESULTS

Women experiencing chemical pregnancies had a higher frequency of APA than women with implantation failure associated with a negative pregnancy test (80% versus 28%, P < 0.0001). The prevalence of ANA, elevated NK cells and ETA was not different between the two groups. The mean gestational sac size from 24 to 35 days from LMP did not differ when chemical pregnancies were compared with pregnancies progressing longer than 35 days. The maximal gestational sac diameter among chemical pregnancies was 3.8 mm.

CONCLUSION

Mechanisms involved in implantation failure associated with a negative pregnancy test may be different from those involved in chemical pregnancies. Chemical pregnancies may be the result of defective angiogenesis.

Assisted reproductive technologies: toward improving implantation rates and reducing high-order multiple gestations

Despite striking progress in reproductive medicine over the past quarter century, the number of high-order multiple gestations are unacceptably high, largely as a result of the drive to maintain pregnancy rates in a competitive range. Morphologic criteria are currently used to define the reproductive competence of individual embryos but are imperfect predictors of implantation potential. Current and potential strategies to improve the selection of embryos are described. By the use of several of these approaches, it is hoped that the overall number of embryos that are transferred will be reduced, thereby also reducing the multiple gestation rate.

Preimplantation genetic diagnosis for aneuploidy screening in early human embryos: a review

Embryonic aneuploidies may be responsible for pregnancy failure in many IVF patients. In recent years, fluorescent in situ hybridisation (FISH) for multiple chromosomes has been used to document a high frequency of chromosomal errors and aneuploidy in human preimplantation embryos and, after embryo biopsy, to select embryos that are more likely to implant. Such studies suggest that women with recurrent miscarriage and advanced maternal age may benefit most from preimplantation genetic diagnosis with aneuploidy screening (PGD-AS). The success of PGD-AS is likely to be enhanced by new technologies, such as comparative genomic hybridisation, which enable full karyotyping of single cells.

Rigorous thermal control during intracytoplasmic sperm injection stabilizes the meiotic spindle and improves fertilization and pregnancy rates

OBJECTIVE

To examine the effects of different thermodynamic control systems on the temperature stability of human eggs during in vitro manipulation, with the integrity of meiotic spindles imaged using the LC-PolScope (Cambridge Research & Instrumentation, Inc., Woburn, MA).

DESIGN

We performed intracytoplasmic sperm injection (ICSI) and/or imaging of eggs with the temperature regulated by three different systems: thermostated coverslip (system 1), thermostated coverslip combined with objective heater (system 2), and conventional stage warmer (system 3).

SETTING

Academic in vitro fertilization clinic.

PATIENT(S)

Oocytes were aspirated from stimulated ovaries of patients undergoing oocyte retrieval for ICSI.

INTERVENTION(S)

Measurement of temperature regulation in media surrounding eggs during in vitro manipulation and imaging.

MAIN OUTCOME MEASURE(S)

Rate of oocytes with spindles, fertilization rates, and clinical pregnancy rates after ICSI.

RESULT(S)

We imaged spindles in more oocytes with system 2 (81.2%) than with system 1 (61.4%). Spindles could not be imaged for system 3 because of technical limitations. Fertilization rates were significantly higher when oocytes were imaged and used for ICSI with system 2 (78.8%) than with system 1 (56.7%) or system 3 (64.0%). Most importantly, a significantly higher clinical pregnancy rate was observed when oocytes were manipulated with system 2 (51.7%) than with system 1 (25.0%) or system 3 (23.1%). No differences were found in average ages, number of previous cycles, number of eggs, or day 3 FSH or E2 levels among groups.

CONCLUSION(S)

Imaging meiotic spindles with the PolScope provides an intracellular thermostat during ICSI. Rigorous thermal control during ICSI stabilized spindles and increased the fertilization and clinical pregnancy rates achieved after ICSI. The presence of birefringent spindles in living human eggs served as a monitor for in vitro conditions.

Oocyte-induced haploidization

This paper describes the technical approach to treatment of age-related oocyte aneuploidy. Although one solution can be oocyte/embryo selection, another is represented by the nuclear transplantation procedure. The efficiency of nuclear transplantation into immature oocytes is described as a way of generating embryos, and the possibility that viable female gametes can be constructed by transfer of diploid somatic cell nuclei into enucleated oocytes. Germinal vesicle (GV)-stage mouse oocytes were collected from unstimulated ovaries and somatic nuclei were obtained from mouse cumulus cells obtained after ovarian stimulation. Spare human GV-stage oocytes were donated from consenting patients undergoing intracytoplasmic sperm injection (ICSI) treatment, and human somatic cells were stromal cells coming from uterine biopsies performed on consenting patients undergoing endometrial cell co-culture. GV ooplasts, prepared by enucleation, were transplanted with either GV or somatic nuclei by micromanipulation. Grafted oocytes were electrofused and cultured to allow maturation, following which they were selected at random for insemination or cytogenetic analysis. GV transplantation was accomplished with an overall efficiency of approximately 80 and 70% in the mouse and the human respectively. The maturation rate of 96% (mouse) and 62% (human) following reconstitution was comparable to that of control oocytes, as was the incidence of aneuploidy among the reconstituted oocytes. The reconstituted human oocytes were successfully fertilized by ICSI at a rate of 52%. After the transfer of mouse cumulus or human endometrial cell nuclei into enucleated immature oocytes, a polar body was extruded in >40%. In a limited number of observations where the nucleus of an aged oocyte was transferred into a younger ooplasm, the chromosomes segregated normally at the time of polar body extrusion. The technique of nuclear transplantation itself did not increase the incidence of chromosomal anomalies in the mouse or human, since their oocytes reconstituted with homologous donor GV resumed meiosis to metaphase II and maintained a normal ploidy. In addition, immature mouse ooplasts induced haploidization of transplanted somatic cell nuclei. Although further evaluation of their genetic status is needed, the procedure may offer a realistic way of producing normal oocytes in cases of aged-related infertility. While the procedure is technically similar to cloning, it would generate a unique individual as a result of the contribution of both parental genomes.

Different probe combinations for assessment of postzygotic chromosomal imbalances in human embryos

PURPOSE

We compared three different probe combinations for detection of postzygotic mosaic imbalances in human preimplantation embryos.

METHODS

Two hundred and two spare cleavage stage embryos were hybridized with fluorescently labelled DNA probe mixtures specific to chromosomes X, Y, 18 (N = 67), chromosomes 2, 7, 18 (N = 71), or chromosomes 13, 16, 18, 21, 22 (N = 64).

RESULTS

An overall higher incidence of abnormalities was detected using probe mixture for five (69%) or three (72%) autosomes compared to one autosome and chromosomes X and Y (54%). The rate of aneuploidy detected increased with the number of autosomes hybridized from 4% (X, Y, 18) to 11% (2, 7, 18) to 19% (13, 16, 18, 21, 22). Postzygotic mosaicism comprised the most frequent abnormality detected by all probe combinations, and the percentage detected by each was similar, 48% (X, Y, 18), 56% (2, 7,18), and 50% (13,16,18, 21, 22).

CONCLUSIONS

A probe combination of five autosomes, particularly those of clinical relevance, may be more beneficial for screening embryos from patients at risk of maternal-age-related aneuploidy. However, all three probe combinations are as efficient at identifying postzygotic mosaicism, and may be used for identifying embryos with less potential of developing to term.

Preimplantation genetic diagnosis of numerical and structural chromosome abnormalities

The causes of the decline in implantation rates observed with increasing maternal age are still a matter for debate. Data from oocyte donation strongly suggest that in women of advanced reproductive age, the ability to become pregnant is largely unaffected while oocyte quality is compromised. The incidence of chromosomal abnormalities in embryos is considerably higher than that reported in spontaneous abortions, suggesting that a sizable percentage of chromosomally abnormal embryos are eliminated before any prenatal diagnosis. Such loss may partly account for the decline in implantation in older women. Because of the correlation between aneuploidy and reduced implantation, it has been postulated that selection of chromosomally normal embryos could reverse this trend. Preimplantation genetic diagnosis (PGD) for aneuploidy had three objectives relevant to the present paper: (i) to increase rates of implantation, (ii) to reduce risks of spontaneous abortion, and (iii) to avoid chromosomally abnormal births. Implantation rates did not increase when only five chromosomes were analysed in blastomeres. With eight chromosomes, a significant increase in implantation was achieved. PGD can significantly reduce the incidence of spontaneous abortion. In our clinic, a significant decrease in spontaneous abortions was found, from 23 to 11% after PGD. Currently in cases diagnosed at Saint Barnabas, 0.8% chromosomally abnormal conceptions have been observed after PGD versus an expected 3.2% in a control age-matched group. It seems clear that PGD reduces the possibility of trisomic conceptions under all conditions. If a couple's main interest is to improve their chances of conceiving (improve implantation), then one should consider maternal age and number of available embryos. Improvements in conception after PGD again increase after 37 years of age with eight or nine probes. Carriers of translocations are at a high risk of miscarriage or chromosomally unbalanced offspring, and a high proportion have secondary infertility. PGD of translocations has been approached through a variety of methods, here reviewed, and has resulted in a significant reduction in spontaneous abortions. However, implantation rates in translocation carriers are directly correlated with the proportion of normal gametes, and male patients with 70% or more unbalanced spermatozoa have great difficulty in achieving pregnancy with PGD.

Preimplantation genetic diagnosis in clinical practice

Preimplantation genetic diagnosis (PGD) represents an alternative to prenatal diagnosis and allows selection of unaffected IVF embryos for establishing pregnancies in couples at risk for transmitting a genetic disorder.

Aspects of biopsy procedures prior to preimplantation genetic diagnosis

Today, preimplantation genetic diagnosis (PGD) is offered in over 40 centres worldwide for an expanded range of genetic defects causing disease. This very early form of prenatal diagnosis involves the detection of affected embryos by fluorescent in situ hybridization (FISH) (sex determination or chromosomal defects) or by polymerase chain reaction (PCR) (monogenic diseases) prior to implantation. Genetic analysis of the embryos involves the removal of some cellular mass from the embryos (one or two blastomeres at cleavage-stage or some extra-embryonic trophectoderm cells at the blastocyst stage) by means of an embryo biopsy procedure. Genetic analysis can also be performed preconceptionally by removal of the first polar body. However, additional information is then often gained by removal of the second polar body and/or a blastomere from the embryo. Removal of polar bodies or cellular material from embryos requires an opening in the zona pellucida, which can be created in a mechanical way (partial zona dissection) or chemical way (acidic Tyrode's solution). However, the more recent introduction of laser technology has facilitated this step enormously. Different biopsy procedures at different preimplantation stages are reviewed here, including their pros and cons and their clinical applications. The following aspects will also be discussed: safety of zona drilling by laser, use of Ca2+/Mg2+-free medium for decompaction, and removal of one or two cells from cleavage-stage embryos.