The development of fertilized human ova to the blastocyst stage in KSOM(AA) medium: is a two-step protocol necessary?

Birefringence parameter available for quantitative analysis of human zona hardness

This study was designed to investigate whether a non-invasive birefringence parameter, determined using the Oosight™ imaging system, is useful for estimating the hardness of human zona pellucida (ZP). The value for retardance (R) × thickness (T), but not R or T alone, of ZP was positively correlated (r = 0.92, p < 0.0001) with its hardness estimated by the time required for a 0.1% protease solution to solubilize ZP at 37 °C. In a model experiment to induce ZP puncture by Fluorinert™ fluid microinjection (sham-hatching), the R × T value at the punctured site was positively correlated (r = 0.78, p < 0.01) with the hardness of the ZP as estimated by the maximum expansion rate. The R × T values of ZP in in vitro fertilization-derived embryos (21.6 ± 7.5) and intracytoplasmic sperm injection-derived embryos (20.8 ± 6.3) were significantly higher than that in unfertilized metaphase II oocytes (16.6 ± 6.1; p < 0.05). The R × T value after in vitro hatching of viable blastocysts (10.8 ± 6.2) was significantly lower than that of unexpanded morulae and early blastocysts (19.0 ± 4.0; p < 0.05), while the value of expanding blastocysts (15.3 ± 4.1) was intermediate. In conclusion, hardness of human ZP can be estimated non-invasively by birefringence-based microscopic observation.

Early embryo development in a sequential versus single medium: a randomized study

BACKGROUND

The success of in vitro fertilization techniques is defined by multiple factors including embryo culture conditions, related to the composition of the culture medium. In view of the lack of solid scientific data and in view of the current general belief that sequential media are superior to single media, the aim of this randomized study was to compare the embryo quality in two types of culture media.

METHODS

In this study, the embryo quality on day 3 was measured as primary outcome. In total, 147 patients younger than 36 years treated with IVF/ICSI during the first or second cycle were included in this study. Embryos were randomly cultured in a sequential (group A) or a single medium (group B) to compare the embryo quality on day 1, day 2 and day 3. The embryo quality was compared in both groups using a Chi-square test with a significance level of 0.05.

RESULTS

At day 1, the percentage of embryos with a cytoplasmic halo was higher in group B (46%) than in group A (32%). At day 2, number of blastomeres, degree of fragmentation and the percentage of unequally sized blastomeres were higher in group B than in group A. At day 3, a higher percentage of embryos had a higher number of blastomeres and unequally sized blastomeres in group B. The number of good quality embryos (GQE) was comparable in both groups. The embryo utilization rate was higher in group B (56%) compared to group A (49%).

CONCLUSIONS

Although, no significant difference in the number of GQE was found in both media, the utilization rate was significantly higher when the embryos were cultured in the single medium compared to the sequential medium. The results of this study have a possible positive effect on the cumulative cryo-augmented pregnancy rate.

TRIAL REGISTRATION NUMBER

NCT01094314.

What does an embryo need?

This review argues that the question "What does an embryo need?" cannot be adequately answered in quantitative terms to allow the formulation of media for culturing early mammalian embryos. It can be shown experimentally that "needs" in terms of the nutrients an embryo chooses to consume, and their rates of consumption, vary widely, as they are determined by the concentration of the nutrients under consideration and other constituents in the culture medium. Similarly, it is impossible to define "needs" from knowledge of the kinetic properties of nutrient transport systems. Measurements of nutrient consumption, are, however, valuable in determining overall metabolic activity and the balance between oxidative and glycolytic metabolism, in demonstrating qualitative requirements for specific nutrients and in providing markers of normality or abnormality against which to devise methods for diagnosing embryo health. On the basis of these and other considerations, a strategy is proposed for the formulation of embryo culture media that promotes metabolism that is "quiet" rather than "active", reduces the concentrations of nutrients to match those in the Fallopian tube, selects the "quietest" embryos for transfer, and trusts the autonomy of the embryo.

Clinical predictors of human blastocyst formation and pregnancy after extended embryo culture and transfer

OBJECTIVE

To determine the clinical factors associated with blastocyst development and pregnancy.

DESIGN

Evaluation of a prospectively collected IVF database.

SETTING

An academic IVF practice.

PATIENT(S)

Couples (n = 529) undergoing their first IVF cycle who qualified for extended embryo culture (more than six zygotes) over the past 5 years.

INTERVENTION(S)

Seven or eight zygotes were cultured for 5 days, assessed for quality, and then transferred with excess zygotes cryopreserved at the pronuclear stage.

MAIN OUTCOME MEASURE(S)

Clinical predictors of blastocyst development and pregnancy.

RESULT(S)

The mean blastocyst development rate was 49.8%, with a median number of total and good-quality blastocysts of 4 and 2, respectively. Clinical factors that were significantly associated with good-quality blastocyst formation were younger female age, increased parity, standard insemination, and lower doses of gonadotropins. Clinical factors that were significantly associated with successful pregnancy were younger female age, higher antral follicle counts, greater numbers of total and good-/excellent-quality blastocysts, and absence of male factor infertility.

CONCLUSION(S)

Several clinical factors are associated with the development of good-quality blastocysts after extended embryo culture and successful pregnancy outcome. These patient and cycle characteristics may be very useful in selecting the best candidates for extended embryo culture and single blastocyst transfers, thus optimizing outcomes while reducing the risks associated with multiple pregnancies.

Choosing a culture medium: making informed choices

OBJECTIVE

To analyze critically the reasons justifying the choice of two-step protocols requiring two media for the culture of human preimplantation embryos from the zygote to the blastocyst.

DESIGN

Literature review.

RESULT(S)

Two types of protocol are used for the culture of human preimplantation embryos from the zygote to the blastocyst, using either one medium (one-step protocol) or two media of different composition (two-step protocol). Two-step protocols are the most widely used, largely because all but one of the commercially available protocols are of this type. The reasons for the adoption of two-step protocols are described and critically analyzed. They are based on considerations of the functions of glucose, ethylenediaminetetraacetic acid (EDTA), glutamine, and amino acids that are included in the media. A reappraisal of the reasons for selecting two-step protocols is important because recent animal experiments and clinical observations have raised doubts as to whether the more complex, two-step protocols have any advantage over one-step protocols. The analyses show that all of conclusions reached should be considered equivocal.

CONCLUSION(S)

Clinical embryologists should evaluate the justification for selecting two-step protocols for the culture of human preimplantation embryos from the zygote to the blastocyst.

Culturing in vitro produced blastocysts in sequential media promotes ES cell derivation

Embryonic stem (ES) cell lines are routinely derived from in vivo produced blastocysts. We investigated the efficiency of ES cells derivation from in vitro produced blastocysts either in monoculture or sequential culture. Zygotes from hybrid F1 B6D2 mice were cultured in vitro to the blastocyst stage in Potassium (K(+)) simplex optimised medium (KSOM) throughout or in KSOM and switched to COOK blastocyst medium on day 3 (KSOM-CBM). Blastocysts were explanted on a feeder layer of mitomycin C-inactivated murine embryonic fibroblasts (MEF) in TX-WES medium for ES cell derivation. Sequential KSOM-CBM resulted in improved blastocyst formation compared to KSOM monoculture. ES cells were obtained from 32.1% of explanted blastocsyts cultured in KSOM-CBM versus 18.4% in KSOM alone. ES cell lines were characterized by morphology, expression of SSEA-1, Oct-4 and alkaline phosphatase activity, and normal karyotype. These results indicate that in vitro culture systems to produce blastocysts can influence the efficiency of ES cell line derivation.

Effects of culture medium on HCG concentrations and their value in predicting successful IVF outcome

The hypothesis was tested that the medium used to culture embryos affects the concentration of human chorionic gonadotrophin (HCG) early in pregnancy. The value of these concentrations in predicting successful outcome was also assessed for each medium studied. Patients undergoing IVF between January 1998 and December 2004 and having a day 3 embryo transfer were stratified into one of four groups according to the medium in which their embryos were cultured (P1, IVF500, G1.2, and G1.3). Using receiver operating characteristic (ROC) curve analysis, cut-off values for serum HCG concentrations on day 15 after embryo transfer were calculated for optimal discrimination between cycles resulting in implantation failure and success for each medium. Cut-off points were chosen to maximize sensitivity and specificity. For viable singleton pregnancies, mean HCG concentrations were greater for G1.3 and lower for IVF500 compared with the other media. Discriminatory HCG cut-off concentrations for predicting implantation success were lowest for IVF500, intermediate for P1 and G1.2 and highest for G1.3. The data support the hypothesis that the medium used to culture embryos significantly affects the concentrations of HCG early in pregnancy. Furthermore, when using HCG cut-off concentrations to assess pregnancy outcome, medium type should be taken into consideration.

Cytoplasmic pitting has a negative influence on implantation outcome

PURPOSE

Since cytoplasmic pitting is a morphological phenomenon discussed controversially, this study was set up in order to assess the actual influence of cytoplasmic pitting on treatment outcome.

METHODS

Four hundred and one patients undergoing 484 consecutive treatment cycles were evaluated retrospectively in order to assess the actual influence of pitting on treatment outcome.

RESULTS

Pitting was found to be reduced in single culture as compared to group culture (p < 0.01). No correlation of cytoplasmic texture with rates of implantation and pregnancy could be observed, but a significantly higher proportion (p < 0.05) of gestational sacs vanished in the group with exclusive transfer of pitted embryos compared to the unaffected group. Obstetric and perinatal outcome was not affected.

CONCLUSIONS

It is possible that culture conditions favor cytoplasmic pitting, a morphological phenomenon which, in the extreme case, may result in early loss of gestation sacs.

One-step versus two-step culture of mouse preimplantation embryos: is there a difference?

BACKGROUND

A comparison has been made of the development of mouse zygotes in either one-step or two-step culture systems.

METHODS

Embryo culture, blastocyst cell counts and embryo transfer were done.

RESULTS

No significant differences were observed in the proportions of blastocysts, rates of hatching, numbers of cells in the inner cell mass (ICM) and trophectoderm (TE) that developed in protocols: one-step culture in potassium-enriched simplex optimized medium supplemented with glucose and amino acids (KSOMg(AA)), two-step culture in KSOMg(AA)/KSOMg(AA), and two-step culture in G1.2/G2.2. No gross abnormalities were observed in the fetuses that developed from zygotes in the one-step protocol using KSOMg(AA) and a two-step protocol using G1.2/G2.2. The body weights of these two groups of fetuses were not significantly different and no developmental abnormalities were observed. No significant differences were observed in the proportions of blastocysts, rates of hatching, numbers of cells in the ICM and TE that developed in protocols: one-step culture in KSOMg(AA), two-step culture in KSOMg(AA)/KSOMg(AA), and two-step culture in DM2/DM1. EDTA is not toxic to the initial cleavage stages of development at a concentration of 0.01 mmol/l in KSOMg(AA).

CONCLUSIONS

Two-step culture protocols are sufficient for the support of preimplantation mouse development in vitro but they are not necessary.

Increases in phosphorylation of SAPK/JNK and p38MAPK correlate negatively with mouse embryo development after culture in different media

OBJECTIVE

To test whether signal transduction proteins that mediate stress may be used to detect responses of embryos to different media in a prospective randomized study.

DESIGN

Controlled laboratory study.

SETTING

None.

PATIENT(S)

None.

INTERVENTION(S)

Mouse embryos isolated at E3.5 (3.5 days after fertilization) or E1.5 were cultured in different media for 24 hours or 72 hours, respectively. Expression of p38 mitogen activated protein kinases (MAPKs) and stress-activated protein kinase/Jun kinase (SAPK/JNK) phosphoproteins in the mouse embryo and their correlation with preimplantation development were studied.

MAIN OUTCOME MEASURE(S)

[1] In E3.5 embryos, SAPK/JNK and p38MAPK are phosphorylated at different levels in different media after 24 hours, with Ham's F10+BSA and M-16 having the highest intensity of both SAPK/JNK and p38MAPK phosphorylation and Quinn's cleavage medium and potassium simplex optimized medium supplemented with amino acids (KSOM+AA) the lowest intensity. [2] The stress-induced increase in phosphorylation of SAPK/JNK and p38MAPK appears to be post-translational in embryos. [3] The intensity of SAPK/JNK phosphorylation measured at E1.5+72 hours culture is inversely correlated with 4-cell/compaction rate, morula formation rate, blastocyst formation rate, and hatching rate.

RESULT(S)

SAPK/JNK and p38MAPK phosphoprotein levels, but not all forms of protein, are affected during culture of preimplantation embryos in seven different media. During culture, the rate of progress to four developmental events was assayed and each rate was inversely proportional to the level of SAPK/JNK phosphorylation measured by immunocytochemical means or Western blot analysis at the end of culture.

CONCLUSION(S)

Culture stresses embryos; different media exert different levels of stress on the embryos. There is a negative correlation between the amount of stress and the development rate. Taken together, the data suggest that SAPK/JNK phosphorylation may constitute a measure of homeostatic response to negative stimuli of media.

Is there still a place for co-cultures in the era of sequential media?

Co-cultures have been advocated in assisted reproduction owing to the inadequacy of simple media to support embryo development beyond the cleavage stage. Different human and non-human cells and cell lines have been used for co-cultures. High rates of blastocyst formation have been reported with the use of co-cultures, and they have been proposed as a salvage treatment option in couples with repeated implantation failures. Since the advent of complex sequential media, which yield very high blastocyst formation and blastocyst implantation rates, the need for co-cultures has been questioned. Upon review of the literature, it is evident that well-designed randomized studies that compare co-cultures with simple or sequential media do not exist. Progression to the blastocyst stage for cleavage stage embryos appears to be similar, if not better, for embryos that are cultured in modern sequential media, rendering the use of co-cultures obsolete. Furthermore, there is no consensus regarding the necessity of sequential media, as similar results have been obtained with a single medium formulation that supports all stages of the preimplantation period. Whether co-cultures are beneficial in patients with repeated implantation failures, however, should be investigated in randomized trials. Co-cultures still serve as powerful tools for understanding embryo metabolism. Furthermore, co-cultures may be instrumental in studying expression of implantation-related genes and embryo-endometrium interaction.

Comparison of two sequential media for culturing cleavage-stage embryos and blastocysts: embryo characteristics and clinical outcome

This study was undertaken to compare the outcome of day 3, day 5, and frozen-thawed embryo transfer cycles where embryo culture was undertaken using the G1.2-G2.2 versus GIII series sequential media. A total of 400 day 3, 73 day 5 and 126 frozen-thawed embryo transfer cycles were analysed. Treatment cycles were quasi-randomized on the day of oocyte retrieval to embryo culture in G1.2-G2.2 versus GIII series sequential media. Randomization was undertaken according to alternating weekdays. Significantly more embryos were of grade 1 or 2 quality on day 3 in the GIII group (P < 0.05). Likewise, more embryos in the GIII group had eight blastomeres on day 3 (P < 0.05) and were able to hatch spontaneously (P < 0.05). For day 3 embryo transfer cycles, implantation and clinical pregnancy rates were 14.4 and 25.7% versus 37.8 and 50.3% in G1.2-G2.2 and GIII groups respectively (P < 0.05). For day 5 embryo transfer cycles, implantation rates were significantly higher (29 versus 45%; P < 0.05) in the GIII group. There was a trend towards higher pregnancy rates; however, this did not reach statistical significance due to fewer cycles analysed in this group. In-vitro culture in GIII series sequential media yields better quality embryos that implant more efficiently, compared with culture in G1.2-G2.2 media.

Critical evaluation of human blastocysts for assisted reproduction techniques and embryonic stem cell biotechnology

Critical examination of 30 blastocysts by transmission electron microscopy (TEM) reveals cellular features not usually evident, including abnormalities of cell structure and aberrations such as multinucleation, internal fragmentation, phagocytic or degenerating cells. Invariably, such blastocysts are inactive and delay or fail to expand and hatch in vitro. Hatching seems to be a major problem in ageing blastocysts due to inactivity of the surface epithelium of trophoblast cells that do not stretch and expand. These lack surface microvilli and contractile tonofilaments that anchor on to specialized cell junctions such as desmosomes. Trophoblast expansion and consequent thinning of the zona is a prerequisite to proper hatching aided by the hydrostatic pressure in the blastocoele and by specialized cells at hatching points. Proper assessment of the inner cell mass is required if a healthy population of cells is to be harvested for embryonic stem cell culture. An inactive blastocyst is obviously not good material and could have a defective inner cell mass (ICM). Normally approximately 3-5% of cells are mitotic in blastocysts and arrested cell division is also an indicator of inactivity. An attempt has been made to evaluate blastocyst internal structure for both assisted reproduction techniques and embryonic stem cell biotechnology.

Development of culture media for human assisted reproductive technology

Contemporary culture systems in human assisted reproductive technologies meet the metabolic needs of preimplantation embryos by addressing energetic and amino acid requirements in a stage-specific manner. This approach significantly enhances viability compared with the historical use of simple salt solutions or complex somatic cell media.

Towards a single embryo transfer

The delivery of a single, healthy child is the desired outcome of human assisted reproduction techniques. To attain this goal, there is an increasing movement toward single embryo transfer. The question is, therefore, at what stage to transfer the human embryo back to the uterus? Maximal implantation rates reported to date have come from the transfer of blastocysts (70% fetal heart rate). In any given cycle of treatment the probability of conceiving a child will be further increased by the ability to cryopreserve those embryos not transferred. It is therefore proposed that the transfer of a single blastocyst is the best treatment for most patients, given the high implantation rates of fresh transfers, and that it is now possible to cryopreserve supernumerary blastocysts effectively. The next decision is how to culture the human embryo to the blastocyst stage. The use of sequential culture media, designed not only to allow for changes in nutrient requirements and metabolism as development proceeds, but also to minimize intracellular trauma, can facilitate the development of highly viable blastocysts. Sequential culture media have been evaluated against a single-step culture system. It has been shown that sequential media (G1/G2) produce more viable blastocysts than those embryos cultured in a single medium formulation (simplex optimized medium with elevated potassium and with amino acids, KSOM(AA)) throughout the preimplantation period. Furthermore, even if KSOM(AA) is used for embryo culture, it is essential that the medium be renewed after 48 h to alleviate the toxicity associated with ammonium build-up. Of great significance, embryos cultured in sequential media G1 and G2 have the same rate of development as embryos developed in vivo.

Tribute to Georgeanna and Howard Jones

This tribute is divided into three sections. The first of these is a description of six weeks of research involving Georgeanna and Howard Jones and me over a few weeks in Johns Hopkins in 1965. Initially, it describes details of preliminary work and then completion of the maturation programme of the mature human oocyte and the first serious attempts at IVF. Scientific discoveries in those exciting weeks contributed to the earliest beginnings of IVF. A second section on knowledge of the human preimplantation embryo today concentrates on the problem of poor-quality embryos and how to overcome it, and on new knowledge on the regulation of human embryonic development. Lastly, the ethics of assisted conception are debated in relation to early practice and to some international features of modern ethical adjudication. A brief conclusion describes some of the friendships initiated in Johns Hopkins and still intact today.

Aspects of the molecular regulation of early mammalian development

Many regulatory systems operate in the early mammalian embryo. This brief overview surveys several systems and their integration including polarities and axes, left-right differentiation, timers in cells, tissues and in gene expression, and imprinting. Polarities are essential from the very earliest stages of oocyte formation, and maintain their significance until blastocyst stages and beyond. They determine cleavage axes and the distribution of maternal proteins in the oocyte, distinct distributions being identified at the animal pole especially. Left-right axes are no doubt expressed from the earliest embryonic stages, and perhaps even in determining slight differences in the axes of cleavage and of maternal protein distribution. Timers, equally fundamental, have been demonstrated to control many functions in oocytes and embryos. Many fundamental processes in early mammalian oocytes and embryos are closely timed. They are classified into circadian rhythms, hourglass timers, clocks regulating major aspects of development including transcription, longevity via telomere clocks and long-range systems. Imprinting and methylation, increasingly important in establishing stable phenotypes in early embryos, might develop abnormally under some circumstances including intracytoplasmic sperm injection and cloning. A general summary briefly describes some other aspects of regulation, especially chromosomal anomalies in human embryos.

Blastocyst culture: facts and fiction

The use of sequential media has made extended culture and transfer of blastocysts feasible for human IVF. Embryo transfer on day 5 has been claimed to result in higher implantation rates than transfer on day 3, on the basis of retrospective comparative studies. This is not supported convincingly, however, in randomized controlled trials published to date. Blastocyst culture imposes additional requirements in terms of personnel, equipment, education and cost and is associated with a greater incidence of monozygotic twinning and cycle cancellation rate than in the case of day 3 culture. In order for day 5 transfer to replace day 3 transfer, a convincing comparison between the two methods should therefore demonstrate the superiority of blastocyst transfer. There is still a need for properly designed randomized controlled trials to compare day 3 with day 5 transfer which will also address the effectiveness of a single blastocyst replacement in reducing the incidence of multiple pregnancies as well as the value of blastocyst cryopreservation.