Preimplantation genetic diagnosis

Preimplantation genetic diagnosis (PGD) is the screening of embryos at the cleavage stage in order to select and transfer only the desired embryo. The main indications of PGD are monogenic disorders and aneuploidy. This article reviews the recent advances in PGD methodology and presents their advantages, disadvantages and challenges. Ethical considerations arising with more widespread use of PGD for physical traits is also discussed. PGD for monogenic disorders remains the most successful indication, but is technically more challenging. PGS for aneuploidy has passed through a period of reconsideration and is now re-emerging with complete genome screening.

Follicular and luteal phase endometrial thickness and echogenic pattern and pregnancy outcome in oocyte donation cycles

PURPOSE

To study the effect of endometrial thickness (ET) and echogenic pattern (EP) in oocyte donation cycles upon pregnancy outcomes.

METHODS

Seventy-nine cycles resulting in blastocyst embryo transfer were evaluated. Donors underwent ovarian hyperstimulation using rFSH and GnRH-antagonist. Recipients were synchronized to donors using GnRH-agonist down-regulation followed by fixed dose of estrogen (E2) and progesterone (P4) following hCG. Transvaginal ultrasound (US) obtained ET and EP 10-11 days after initiation of E2 and on day of embryo transfer. Primary outcome was ET and EP in pregnant and non-pregnant cycles. Stimulation and embryology data was analyzed in donors to assess differences prior to transfer.

RESULTS

Fifty-nine cycles resulted in clinical pregnancy. No differences were observed in pregnant vs. non-pregnant cycles in proliferative or secretory ET and EP. Similar baseline and stimulation characteristics were found in pregnant and non-pregnant cycles. Regression analysis showed end thickness were not predictive of pregnancy outcomes.

CONCLUSIONS

Endometrial characteristics in recipients prior to and following progesterone were not predictive of pregnancy outcomes.

Effect of a woman's smoking status on oocyte, zygote, and day 3 pre-embryo quality in in vitro fertilization and embryo transfer program

In the present study we investigated the effect of a woman's smoking status on the quality of the oocyte, zygote, and on day 3 pre-embryo, as well as the likelihood of achieving an ongoing pregnancy at 8 weeks. Smokers presented a higher number of nonfertilized oocytes than nonsmokers (20.1% vs. 10.8% of fertilization failure), by comparable clinical pregnancy rate for smokers (40.8%; 28/72) and for nonsmokers (39.2%; 23/58).

Male age negatively impacts embryo development and reproductive outcome in donor oocyte assisted reproductive technology cycles

OBJECTIVE

To determine whether male age influences embryo development and reproductive potential in assisted reproductive technology cycles.

DESIGN

Retrospective cohort analysis.

SETTING

Private IVF center.

PATIENT(S)

One thousand twenty-three male partners participating in anonymous oocyte donation cycles.

INTERVENTION(S)

Infertile couples undergoing 1,023 anonymous oocyte donation cycles.

MAIN OUTCOME MEASURE(S)

Live birth rate.

RESULT(S)

A significant increase in pregnancy loss, decrease in live birth rate, and decrease in blastocyst formation rate were noted in men >50 years of age. There was no significant difference in implantation rate, pregnancy rate, or early embryo development through the cleavage stage (demonstrated by fertilization rate, embryo cleavage rate, percentage of nonfertilized or polyspermic embryos, rate of embryo arrest, or seven or more cell embryo development on day 3). Men < or =45 years of age had significantly more semen volume and more motile sperm than men >45 years of age. There was no significant change in sperm morphology or concentration.

CONCLUSION(S)

After controlling for female age with use of the donor oocyte model, male age >50 years significantly affected pregnancy outcomes and blastocyst formation rates. Semen volume and total motility decreased with increasing male age. Initial embryo morphology through the cleavage stage was not affected.

[Influence of "zero" magnetic field on the growth of embryonic cells and primary embryos of mouse in vitro]

The present investigation reveals that a 250-fold screening of the geomagnetic field ("zero" geomagnetic fields, 200 nT) is a biologically active factor that adversely affects embryonic cells and the processes of early embryogenesis as a whole. In particular, the cultivation of primary embryonic fibroblasts in "zero" geomagnetic fields causes reduces the capacity for adhesion and proliferation, changes the monolayer morphology and increases cell death. In a more highly organized experimental model, two-celled mouse embryos, the exposure to the "zero" field results in an increase of plasma membrane permeability for dyes, a reorganization of the cytoskeleton because of alpha-actin redistribution, and the disturbance of the spatial orientation of blastomeres. As a result, the development of two-celled mouse embryos stops, and they do not reach the stage of blastocyst. These data show the significant role of geomagnetic fields in the normal growth of embryonic cells in vitro and the regulation of mammalian embryogenesis.

RAX is required for fly neuronal development and mouse embryogenesis

RAX was originally discovered as the unique cellular activator for the dsRNA-dependent, interferon-inducible protein kinase PKR. Recent findings indicate that RAX is also a critical component of the RNA-induced silencing complex and a regulator of transcription. Here we report novel phenotypes for both fruit flies carrying a transposon insertion in the 5' UTR of dRax (independently identified as loqs/R3D1) and mice with a deletion of the entire Rax gene. In Drosophila we observe a high level of dRax expression in the developing nerve cord. Mutant fly embryos homozygous for the insertion dRax[f00791] display highly abnormal commissural axon structure of the CNS and 70% of the flies homozygous for the mutant allele die prior to adulthood. Surviving male flies have reduced fertility and female flies are sterile. Furthermore, these flies appear to have a severe defect in nervous system coordination or neuromuscular function resulting in significantly reduced locomotion. Mice were also generated that are heterozygous for a deletion of the entire Rax gene (exons 1-8). While mice that are heterozygous for the mutant allele are viable and appear normal, we are unable to obtain mice homozygous for this mutant allele. Furthermore, we have not observed any embryo obtained by mating heterozygous mice at either E3.5, 7, or 14 that is nullizygous for the Rax gene. Since Rax is expressed in preimplantation blastocysts, these data indicate that deletion of the entire Rax gene is embryonic lethal in mice at a preimplantation stage of development. Collectively, these findings in two different species illustrate the importance of RAX for embryonic development.

Human immunodeficiency type-1 virus (HIV-1) infection in serodiscordant couples (SDCs) does not have an impact on embryo quality or intracytoplasmic sperm injection (ICSI) outcome

OBJECTIVE

To evaluate the embryo quality in our program for human immunodeficiency type-1 virus (HIV-1) serodiscordant couples (SDCs) with the male infected in comparison with a tubal-factor infertility control group.

DESIGN

Retrospective case-control study.

SETTING

Instituto Valenciano de Infertilidad, Valencia, Spain.

PATIENT(S)

Thirty SDC and 79 control couples without HIV-1 infection attending for intracytoplasmic sperm injection (ICSI). Only first cycles were considered.

INTERVENTION(S)

Controlled ovarian hyperstimulation and ICSI in both groups; sperm wash, nested polymerase chain reaction (PCR) in semen sample, and capacitation by swim-up after thawing the semen sample in the SDC group; and sperm capacitation by swim-up after thawing the semen sample in the control group.

MAIN OUTCOME MEASURE(S)

ICSI procedure and embryo characteristics (fertilization, cleavage, embryo morphology, and development) and cycle outcome (ongoing pregnancy and miscarriage rates).

RESULT(S)

Fertilization and cleavage rates were similar between the groups. On days 2 and 3 of embryo development, very similar embryo features were found between the groups. There was no difference in mean number of optimal embryos on day 3. When embryos were cultured up to 5-6 days, a significant increase in embryo blockage was found in the SDC group compared with the control group. The mean number of optimal blastocysts on day 6 was comparable in both groups. No difference was found regarding the number of cryopreserved and transferred embryos or implantation, pregnancy, multiple pregnancy, or miscarriage rates between the groups.

CONCLUSION(S)

HIV-1 infection in SDCs with infected males does not appear to have a significantly negative impact on embryo development or ICSI outcome.

Impact of hyperglycemia on early embryo development and embryopathy: in vitro experiments using a mouse model

BACKGROUND

The aim of this study is to model the processes of early embryopathy seen in human pregnancy complicated by maternal hyperglycemia secondary to maternal diabetes using a mouse embryo culture system.

METHODS

Female mice were superovulated and mated in pairs. Two-cell embryos were harvested from the oviducts and cultured in vitro in KSOM medium (synthetic oviductal medium enriched with potassium) supplemented with 0.2, 5.56, 15.56 or 25.56 mM d-glucose. Cell proliferation, differentiation and apoptosis were assessed. Experiments were performed in constant, embryos exposed to a particular concentration of glucose (0.2, 5.56, 15.56 or 25.56 mM) from harvest to either Day 5 post fertilization (pf) or Day 8 pf, and fluctuating, embryos exposed to alternate high 25.56 mM and normal 5.56 mM concentrations of glucose between harvest and Day 5 pf, glycemic culture.

RESULTS

Expected levels of blastocyst formation and hatching were seen at 0.2 and 5.56 mM concentrations of glucose but both were impaired at higher concentrations (chi(2), P < 0.005; P < 0.001). Total cell numbers (P < 0.002) and cell allocation to the inner cell mass (P < 0.01) were reduced, but with no evidence of enhanced apoptosis in the hyperglycemic cultures. Variation in hyperglycemic exposure of the embryos on Days 2, 3 and 4 showed no adverse effects of hyperglycemia up to 24 h, but 48 and 72 h exposures were equally embryopathic (P < 0.01).

CONCLUSIONS

Hyperglycemic exposure for >24 h is toxic to early embryo development. These findings may explain the lower than expected implantation rates and higher than expected rates of congenital abnormality and early pregnancy loss seen in patients with diabetes, particularly those with poor diabetic control.

Utérus malformé et Assistance médicale à la procréation: prévention du défaut d'implantation?

The infertility in women with an abnormal uterus seems a subject of controversy. The prognosis of in vitro fertilization among these patients with such an anomaly is even less founded. The results of in vitro fertilization have been only studied with few patients and recently. Through the literature, we will focus step by step, on the impact of uterine anomalies on natural reproduction, then the impact of metroplasty on natural reproduction, the role of anomalies on the endometrium quality and lastly, the results of Assisted Rerpoductive Techniques with women with such an anomaly. It seems that the main risk is obstetric complications such as spontaneous abortion or premature delivery, not implantation failure. However, when infertility exists, surgical treatment tends to improve the pregnancy rate for some.

The influence of sperm morphology on preimplantation genetic diagnosis cycles outcome

OBJECTIVE

To evaluate the impact of abnormal sperm morphology on the rates of aneuploidy, implantation, and clinical pregnancy.

DESIGN

Retrospective cohort study.

SETTING

University-based IVF center.

PATIENT(S)

Fifty-two patients undergoing their first IVF-preimplantation genetic diagnosis (PGD) cycle.

INTERVENTION(S)

The PGD analysis of embryos.

MAIN OUTCOME MEASURE(S)

Patients were divided into two groups based on sperm morphology: teratospermic group (TSG) and normal sperm group (NSG). The primary outcome measures of rates of aneuploidy, implantation, clinical pregnancy rate (PR) per cycle, and clinical PR per embryo transfer were compared between TSG and NSG according to PGD analysis results.

RESULTS

A higher percentage of normal embryos was seen in the NSG (32%) versus the TSG (20%). Overall, 30% of IVF-PGD cycles had no normal embryos for transfer. The clinical PR per cycle was 44% in the NSG compared to 14% in the TSG (relative risk [RR] = 3.19; 95% confidence interval [CI] 1.1-9.0). A similar trend was noted with the clinical PR per embryo transfer with 57% patients becoming pregnant in the NSG versus 20% patients in the TSG (RR = 2.76; 95% CI 1.2-7.2). Implantation was twice as likely to occur in the NSG as compared to TSG (RR = 2.5; 95% CI 1.1-7.2).

CONCLUSION(S)

Rates of euploidy, implantation, clinical PR per cycle, and clinical PR per embryo transfer were higher in the NSG compared to the TSG, suggesting that sperm morphology plays an important role in the outcome of IVF-PGD cycles.

Human embryos developing in vitro are susceptible to impaired epithelial junction biogenesis correlating with abnormal metabolic activity

BACKGROUND

Blastocyst biogenesis occurs over several cell cycles during the preimplantation period comprising the gradual expression and membrane assembly of junctional protein complexes which distinguish the outer epithelial trophectoderm (TE) cells from the inner cell mass (ICM). In the human, TE integrity and the formation of a junctional seal can often be impaired. Embryos likely to result in a successful pregnancy after transfer are mostly selected according to morphological criteria. Recent data suggest that non-invasive measurement of amino acid turnover may be useful to complement such morphological scores. Whether morphological and metabolic criteria can be linked to poor TE differentiation thereby underpinning developmental predictions mechanistically remains unknown.

METHODS

We examined TE intercellular junction formation in human embryos by immunofluorescence and confocal microscopy and correlated this process with morphological criteria and amino acid turnover during late cleavage.

RESULTS

Our results show that TE differentiation may be compromised by failure of membrane assembly of specific junction constituents. This abnormality relates more closely to metabolic profiles than morphological criteria.

CONCLUSION

Our data identify that amino acid turnover can predict TE differentiation. These findings are the first to link two mechanisms, metabolism and junction membrane assembly, which contribute to early embryo development.

Effect of citrinin on mouse embryonic development in vitro and in vivo

Citrinin (CTN), a mycotoxin that is often found as a natural contaminant in foodstuffs and animal feeds, has been demonstrated to have cytotoxic and genotoxic effects on various mammalian cells. In this study, we examined the cytotoxic effects of CTN on mouse blastocysts and subsequent early development in vitro and in vivo. Blastocysts treated with 15 or 30 microM CTN showed significant increases in apoptosis and significant decreases in total cell number. In addition, CTN-pretreated blastocysts showed a significantly lower implantation success rate. Treatment with 30 microM CTN was associated with increased resorption of postimplantation embryos and decreased fetal weight. Our results collectively indicate that CTN-induced apoptosis in the mouse blastocyst reduced cell number and retarded early postimplantation development. The extent to which CTN may have teratogenic potential in early human development is not known.

Day-3 embryo morphology predicts euploidy among older subjects

OBJECTIVE

To evaluate whether day-3 embryo morphology predicts euploidy.

DESIGN

Retrospective.

SETTING

Private IVF center.

PATIENT(S)

Subjects (n = 144) undergoing in vitro fertilization and preimplantation genetic diagnosis (PGD).

INTERVENTION(S)

Translate day-3 embryo characteristics into a standardized score.

MAIN OUTCOME MEASURE(S)

Day-3 embryo morphology score and PGD fluorescence in situ hybridization results for chromosomes: 13, 15, 16, 17, 18, 21, 22, X, and Y.

RESULT(S)

Of 1,043 biopsied blastomeres, 67% (n = 696) were chromosomally abnormal. Women with advanced maternal age (AMA) were 1.3 times more likely to have chromosomal errors (95% CI 1.1-1.4) than younger subjects (<38 years old). Morphology predicted PGD results in the AMA group (n = 553), but not in younger women. Fragmentation predicted euploidy in both the younger and the AMA group, but cell number did not.

CONCLUSION(S)

Day-3 embryo morphology selects for euploidy among AMA subjects but not among younger women who may have other factors responsible for embryo dysmorphism. However, cellular fragmentation is a sensitive proxy for selecting chromosomally normal embryos in both age groups. It is unclear that PGD-aneuploidy screening is a better tool for selecting which embryos to transfer than the standard approach of using day-3 embryo features, particularly among older women, a group for whom this technology is targeted.

Precancerous stem cells have the potential for both benign and malignant differentiation

Cancer stem cells (CSCs) have been identified in hematopoietic and solid tumors. However, their precursors-namely, precancerous stem cells (pCSCs) -have not been characterized. Here we experimentally define the pCSCs that have the potential for both benign and malignant differentiation, depending on environmental cues. While clonal pCSCs can develop into various types of tissue cells in immunocompetent mice without developing into cancer, they often develop, however, into leukemic or solid cancers composed of various types of cancer cells in immunodeficient mice. The progress of the pCSCs to cancers is associated with the up-regulation of c-kit and Sca-1, as well as with lineage markers. Mechanistically, the pCSCs are regulated by the PIWI/AGO family gene called piwil2. Our results provide clear evidence that a single clone of pCSCs has the potential for both benign and malignant differentiation, depending on the environmental cues. We anticipate pCSCs to be a novel target for the early detection, prevention, and therapy of cancers.

The Role of Decidualization in Regulating Endometrial Hemostasis during the Menstrual Cycle, Gestation, and in Pathological States

Progesterone-induced decidualized human endometrial stromal cells form a hemostatic envelope that protects against hemorrhage during invasion of endometrial capillaries by implanting blastocyst-derived cytotrophoblasts (CTs). This hemostatic milieu reflects co-upregulated expression of tissue factor (TF), the primary initiator of hemostasis via thrombin generation and plasminogen activator inhibitor type 1, which inactivates tissue-type plasminogen activator, the primary fibrinolytic agent. During deep invasion of the decidua, CTs breach and remodel spiral arteries and arterioles to produce high-conductance vessels. Shallow invasion results in incomplete vascular transformation and an underperfused fetal - placental unit associated with preeclampsia and intrauterine growth restriction. Decidual hemorrhage and severe thrombophilias elicit aberrant thrombin generation from decidual cell-expressed TF. Such thrombin induces decidual cells to synthesize and secrete soluble fms-like tyrosine kinase-1 (sFlt-1), the matrix metalloproteinases MMP-1 and MMP-3, and the neutrophil chemoattractant interleukin-8. Excess sFlt-1 at the implantation site may inhibit CT invasion by altering the angiogenic factor balance. During abruptions, thrombin-enhanced MMP-1, MMP-3 by decidual cells and neutrophil-derived proteases degrade the decidual and fetal membrane extracellular matrix to promote preterm premature rupture of the membranes. In association with long-term progestin-only contraception, overexpression of decidual cell-derived thrombin promotes aberrant angiogenesis and vessel maintenance to contribute to abnormal uterine bleeding.

Infertility in murine acute Trypanosoma cruzi infection is associated with inhibition of pre-implantation embryo development

We previously showed that Trypanosoma cruzi acute infection induced infertility in a great proportion of female mice, which resulted from a defect taking place before implantation. In this study, we have analyzed every step of reproduction from mating to implantation to identify the most sensitive event. Our results show that mating, ovulation, fertilization, and first division of the zygote of infected mice take place normally compared with uninfected mice, indicating that the defect occurred after the two-cell stage. In vivo development of two-cell embryos to the blastocyst stage was indeed dramatically delayed; some embryos even arrested their development before having reached the eight-cell stage while others degenerated. The effect was less pronounced when embryos were allowed to develop in vitro, indicating that the infectious context of the mother plays a role in maintaining growth retardation. The delay of embryonic development was associated with insufficient divisions of the blastomeres and led to abnormal blastocyst outgrowth that may explain implantation failure. Inhibition of cell division was correlated with the maternal parasitemia. This work clearly shows that T. cruzi infection dramatically impedes embryonic development, offering a model for further in vivo studies of embryotrophic factors produced by the oviduct of infected females.

Molecular cytogenetic studies towards the full karyotype analysis of human blastocysts and cytotrophoblasts

Numerical chromosome aberrations in gametes typically lead to failed fertilization, spontaneous abortion or a chromosomally abnormal fetus. By means of preimplantation genetic diagnosis (PGD), we now can screen human embryos in vitro for aneuploidy before transferring the embryos to the uterus. PGD allows us to select unaffected embryos for transfer and increases the implantation rate in in vitro fertilization programs. Molecular cytogenetic analyses using multi-color fluorescence in situ hybridization (FISH) of blastomeres have become the major tool for preimplantation genetic screening of aneuploidy. However, current FISH technology can test for only a small number of chromosome abnormalities and hitherto failed to increase the pregnancy rates as expected. We are in the process of developing multi-color FISH-based technologies to score all 24 chromosomes in single cells within a three-day time limit, which we believe is vital to the clinical setting. Also, human placental cytotrophoblasts (CTBs) at the fetal-maternal interface acquire aneuploidies as they differentiate to an invasive phenotype. About 20-50% of invasive CTB cells from uncomplicated pregnancies were found to be aneuploid, suggesting that the acquisition of aneuploidy is an important component of normal placentation, perhaps limiting the proliferative and invasive potential of CTBs. Since most invasive CTBs are interphase cells and possess extreme heterogeneity, we applied multi-color FISH and repeated hybridizations to investigate the feasibility of a full karyotype analysis of individual CTBs. In summary, this study demonstrates the strength of Spectral Imaging analysis and repeated hybridizations, which provides a basis for full karyotype analysis of single interphase cells.

A retrospective study of preimplantation embryos diagnosed with monosomy by fluorescence in situ hybridization (FISH)

This report is a retrospective study of preimplantation embryos diagnosed with monosomy for chromosomes 13, 15, 16, 18, 21, 22, X and Y on day 3 to determine the rate of true positives, false positives and/or mosaicism and to assess if these embryos are suitable for in vitro fertilization (IVF) transfer. In a one year period, 80 patients went through preimplantation genetic diagnosis for aneuploidy screening (PGD-AS). Monosomy was diagnosed in 51 embryos. Fluorescence in situ hybridization (FISH) was then performed on the blastomeres at day 5-7 with commercially available probes using the same probe set that initially identified monosomy for chromosomes 13, 16, 21 and 22 or chromosomes 15, 18, X and Y. Based on FISH analysis, the monosomy diagnosed during routine PGD-AS analysis was confirmed in 17 of the 51 embryos. A euploid result for the specific chromosomes tested was observed in 16 of the 51 embryos while mosaicism was found in the remaining 18 embryos. This results in an estimated false positive rate of 3.8% for a diagnosis of monosomy. Reanalysis of these embryos demonstrates that the majority of monosomy diagnoses represents true monosomy or mosaicism and should be excluded for transfer in IVF. Furthermore, improved understanding from recent emerging data regarding the fate of oocytes in women with advanced maternal age undergoing IVF to the development of early embryos may provide a valuable insight into the mechanism of chromosome mosaicism.

Preimplantation genetic diagnosis for Marfan syndrome

OBJECTIVE

To develop and apply efficient and reliable protocols for preimplantation genetic diagnosis (PGD) for Marfan syndrome.

DESIGN

Two mutation-specific protocols were developed, and the markers D15S1028, D15S992, D15S196, D15S576, D15S123, and D15S143 were used to set up four multiplex polymerase chain reactions (PCRs).

SETTING

Research Center Reproduction and Genetics.

PATIENT(S)

Ten couples carrying mutations in the FBN1 gene.

INTERVENTION(S)

Six PGD protocols were developed for 10 couples, and 7 of them underwent a total of 16 clinical cycles.

MAIN OUTCOME MEASURE(S)

Amplification, allele drop-out (ADO), and contamination rates during the preclinical assays. DNA analyses of blastomeres from embryos biopsied during PGD cycles.

RESULT(S)

Six different protocols were set up, with the main objective being to to use one protocol for several couples. A total of 16 PGD cycles were performed, which resulted in the delivery of an unaffected boy and three ongoing pregnancies.

CONCLUSION(S)

The development of single-cell multiplex PCRs for linked markers and its use in PGD reduce the workload of the genetic diagnostic laboratory as well as the average waiting time for patients. This approach also allows for the simultaneous and accurate detection of recombination, contamination, and ADO, thereby increasing the reliability of the diagnosis.

Analysis of DNA methylation profiles in preimplantation embryos using bisulfite mutagenesis

For developmental competence of mammalian embryos, dynamic epigenetic changes to both the maternally and paternally derived contributions to the genome of the zygote should be brought about in the early cleavage stages. DNA methylation is a typical epigenetic mark modified during pre-implantation development. Here, we describe how to analyze DNA methylation profiles in early-stage embryos.

Occurrence and developmental consequences of vacuoles throughout preimplantation development

OBJECTIVE

Since little is known about the actual incidence and fate of vacuoles at different stages of development this preliminary study was set up to accurately measure vacuoles and track them to day 5.

DESIGN

Prospective study.

SETTING

Women's General Hospital in Austria.

PATIENT(S)

A total of 223 consecutive IVF and intracytoplasmic sperm injection (ICSI) cycles (206 patients).

INTERVENTION(S)

Accurate measurement of vacuoles. Affected gametes and embryos were cultured individually and tracked until day 5.

MAIN OUTCOME MEASURE(S)

Size and number of vacuoles, fertilization rate, blastocyst formation rate, blastocyst quality.

RESULT(S)

There was a significant relationship between size of the vacuole (cut-off value 14 microm) and fertilization (P<.05). At zygote stage the incidence of vacuoles was higher (P<.01) in ICSI (11.6%) than in IVF (5.3%). Only 32.2% of affected ICSI-embryos reached blastocyst stage on day 5 compared with 53.0% of the normal ones (P<.001). In terms of blastocyst formation vacuolization on day 4 (P<.001) turned out to be the most severe one. At blastocyst stage inner cell mass was affected less frequently than the trophectoderm (P<.05).

CONCLUSION(S)

Three types of vacuoles could be identified: (1) those already present at oocyte collection, which develop during maturation (day 0); (2) those artificially created by ICSI (day 1); and (3) those accompanied with developmental arrest (day 4). The later that vacuoles arose, the more detrimental their effect on blastocyst formation.

Developmentally retarded frozen blastocysts can be rescued by synchronizing culture prior to transfer

Asynchrony between embryo development and endometrial differentiation is the limiting step of successful pregnancy in assisted reproduction. The aim of this study was to investigate whether or not post-thaw synchronization culture of day 5-6 frozen embryos, prior to transfer, with endometrial differentiation resulted in pregnancy. A total of 142 cycles of 134 patients were transferred in three protocols. Blastocysts with cavities larger than half of the entire blastocyst volume were transferred without synchronizing culture on day 5 or 6 of progesterone commencement (P5/6) in hormone replacement treatment cycles (protocol 1). Blastocysts with cavitation below half of the entire blastocyst were cultured for 1 or 2 days after thawing prior to transfer on P5 or P6 (protocol 2). Morulae and very early stage blastocysts were thawed on the days corresponding to P5 and P6, and only the embryos that reached expanded or hatching blastocysts were transferred on P7 without synchronizing culture (protocol 3). Pregnancy rate in protocol 2 (32.0%) was comparable with that of protocol 1 (35.0%). It is concluded that developmentally retarded frozen embryos can be rescued with synchronizing culture prior to transfer by evading asynchrony.