Effect of cell number at freezing upon survival and viability of cleaving embryos generated from stimulated IVF cycles

The impacts of the number of prefreeze and postthaw blastomeres on embryo implantation potential: A systematic analysis

To systematically analyze the potential of embryo implantation through comparison between the number of surviving blastomeres, the growth, and implantation rate.Retrospective analysis on implantation rate and the growth of prefreeze-postthaw embryos with different blastomeres in 1487 frozen embryo transfer cycles.In groups of postthaw embryos without damage, implantation rate and the average number of blastomere growth increased significantly with increasing number of blastomeres. The implantation rate and the number of blastomeres of embryos with 8-8c (the number of blastomeres in prefreeze embryo-the number of blastomeres in postthaw embryo) continued to grow at a significantly higher rate than that of 5-5c and 6-6c (P < .05). In groups of embryos with the same number of blastomeres before freezing and with partial damage after resuscitation, the implantation rates were lower and the average numbers of blastomere growth reduced as the number of damaged blastomeres increased. For embryos with good quality before freezing, 1 to 3 damaged blastomeres in postthawed embryos did not affect the development and implantation rate. Both implantation rate and growth rate of embryos with 8-6c were significantly higher than those of embryos with 6-6c (P < .05).The number of surviving blastomeres and growth in frozen-thawed embryos could be important index to predict embryo development potential and clinical outcome of implantation. For embryos with good quality, a small amount of damaged blastomeres would not weaken embryo development potential and implantation rate after being thawed.

Cryopreservation of human embryos and its contribution to in vitro fertilization success rates

Cryopreservation of human embryos is now a routine procedure in assisted reproductive technologies laboratories. There is no consensus on the superiority of any protocol, and substantial differences exist among centers in day of embryo cryopreservation, freezing method, selection criteria for which embryos to freeze, method of embryo thawing, and endometrial preparation for transfer of frozen-thawed embryos. In the past decade, the number of frozen-thawed embryo transfer cycles per started in vitro fertilization (IVF) cycle increased steadily, and at the same time the percentage of frozen-thawed embryo transfers that resulted in live births increased. Currently, cryopreservation of human embryos is more important than ever for the cumulative pregnancy rate after IVF. Interestingly, success rates after frozen-thawed embryo transfer are now nearing the success rates of fresh embryo transfer. This supports the hypothesis of so called freeze-all strategies in IVF, in which all embryos are frozen and no fresh transfer is conducted, to optimize success rates. High-quality randomized controlled trials should be pursued to find out which cryopreservation protocol is best and whether the time has come to completely abandon fresh transfers.

Techniques for slow cryopreservation of embryos

The slow cryopreservation of embryos has been used for nearly three decades as a means of storing surplus conceptuses from single IVF (in vitro fertilization) cycles. Doing so has allowed caregivers to maximize pregnancy rates without wastage of precious biological materials. Very detailed methods are described here using a popular biological freezing unit manufactured by Planer PLC (Middlesex, UK). Culture media preparation and tranfer protocols, including replacement in both natural and stimulated cycles, are included.

Preimplantation stress and development

The developmental origins of health and disease hypothesis holds that inappropriate environmental cues in utero, a period marked by tremendous developmental sensitivity, facilitate cellular reprogramming to ultimately predispose disease in adulthood. In this review, we analyze if stress during early stages of development can affect future health. This has wide clinical importance, given that 5 million children have been conceived with assisted reproductive technologies (ART). Because the primary outcome of assisted reproduction procedures is delivery at term of a live, healthy baby, the postnatal effects occurring outside ofthe neonatal period are often overlooked. To this end, the long-term outcome of ART is appropriately the most relevant concern of the field today. Evidence of adverse consequences is controversial. The majority of studies have concluded no obvious problems in IVF-conceived children, although a number of isolated cases of imprinted diseases, cancers, or malformations have been reported. Given that animal studies suggest alteration of metabolic pathways following preimplantation stress, it will be of great importance to follow-up ART individuals as they enter later stages of adult life.

A critical appraisal of cryopreservation (slow cooling versus vitrification) of human oocytes and embryos

BACKGROUND

Vitrification is now a commonly applied technique for cryopreservation in assisted reproductive technology (ART) replacing, in many cases, conventional slow cooling methodology. This review examines evidence relevant to comparison of the two approaches applied to human oocytes and embryos at different developmental stages.

METHODS

Critical review of the published literature using PubMed with particular emphasis on studies which include data on survival and implantation rates, data from fresh control groups and evaluation of the two approaches in a single setting.

RESULTS

Slow cooling is associated with lower survival rates and compromised development relative to vitrification when applied to metaphase II (MII) oocytes, although the vitrification results have predominantly been obtained using direct contact with liquid nitrogen and there is some evidence that optimal protocols for slow cooling of MII oocytes are yet to be established. There are no prospective randomized controlled trials (RCTs) which support the use of either technique with pronuclear oocytes although vitrification has become the method of choice. Optimal slow cooling, using modifications of traditional methodology, and vitrification can result in high survival rates of early embryos, which implant at the same rate as equivalent fresh counterparts. Many studies report high survival and implantation rates following vitrification of blastocysts. Although slow cooling of blastocysts has been reported to be inferior in some studies, others comparing the two approaches in the same clinical setting have demonstrated comparable results. The variation in the extent of embryo selection applied in studies can lead to apparent differences in clinical efficiency, which may not be significant if expressed on a 'per oocyte used' basis.

CONCLUSIONS

Available evidence suggests that vitrification is the current method of choice when cryopreserving MII oocytes. Early cleavage stage embryos can be cryopreserved with equal success using slow cooling and vitrification. Successful blastocyst cryopreservation may be more consistently achieved with vitrification but optimal slow cooling can produce similar results. There are key limitations associated with the available evidence base, including a paucity of RCTs, limited reporting of live birth outcomes and limited reporting of detail which would allow assessment of the impact of differences in female age. While vitrification has a clear role in ART, we support continued research to establish optimal slow cooling methods which may assist in alleviating concerns over safety issues, such as storage, transport and the use of very high cryoprotectant concentrations.

Transfer of human frozen-thawed embryos with further cleavage during culture increases pregnancy rates

AIM:

To compare the pregnancy rate following transfer of frozen-thawed embryos with or without overnight culture after thawing.

SETTINGS AND DESIGN:

This is a retrospective analysis of frozen-thawed embryo transfer (FET) cycles performed between January 2006 and December 2008.

MATERIALS AND METHODS:

Out of 518 thaw cycles, 504 resulted in embryo transfers (ETs). Of the total FET cycles, 415 were performed after an overnight culture of embryos (group A); and in 89 cycles, ET was performed within 2 hours of embryo thawing (group B).

STATISTICAL ANALYSIS:

The data were statistically analyzed using chi-square test.

RESULTS:

We observed that with FET, women ≤30 years of age had a significantly higher (P=0.003) pregnancy rate (PR=28.9%) as compared to women >30 years of age (17.5%). A significantly higher (P<0.001**) pregnancy rate was also observed in women receiving 3 frozen-thawed embryos (29%) as compared to those who received less than 3 embryos (10.7%). The difference in PR between group A (PR=24.3%) and group B (PR=20.3%) was not statistically significant. However, within group A, ET with cleaved embryos showed significantly (P≤0.01) higher pregnancy rate compared to the uncleaved embryos, depending on the number of cleaved embryos transferred.

CONCLUSION:

No significant difference was noticed between FETs made with transfer of embryos with overnight culture and those without culture. However, within the cultured group, transfer of embryos cleaved during overnight culture gave significantly higher PR than transfers without any cleavage.

The application and impact of cryopreservation of early cleavage stage embryos in assisted reproduction

The contribution of cryopreserved embryos to the overall outcomes achieved by a clinical assisted reproduction programme has increased in importance with the trend towards reducing the numbers of fresh embryos transferred following in vitro fertilisation. Although cryopreservation appears to fully preserve developmental potential in early cleavage stage embryos that survive intact, it results in a reduction in potential when blastomere loss occurs during freezing and thawing. Overall, it can be estimated that cryopreservation results in approximately a 30% reduction in the potential for pregnancy in a population of embryos. Both blastomere survival and post-thaw resumption of mitosis can act as markers of implantation potential in frozen/thawed embryos. Application of strict criteria for freezing embryos and transferring thawed embryos may enhance apparent success rates, but may also result in some pregnancy potential being discarded. The role of embryo cryopreservation in minimising the incidence of multiple pregnancy must be balanced with the need for efficiency in the quest to establish pregnancy.

Single embryo transfer in clinical practice

The high incidence of multiple pregnancies is the main reason for adverse treatment outcome in assisted reproduction. A good strategy to avoid multiple pregnancies is elective single embryo transfer and cryopreservation of spare embryos. Important factors in an elective single embryo transfer programme are good counselling of the patients and the selection of embryos with high implantation potential. In the infertility clinic at Helsinki University Central Hospital the elective single embryo transfer programme was started in 1997 and in 2000 the transfer policy turned to single embryo transfer as primary option. In 2003 60% of fresh transfers were elective single embryo transfers and 66% of frozen transfers were single embryo transfers. It has been shown that an elective single embryo transfer programme can be adopted in daily practice and that it decreases the multiple pregnancy rate, in our programme to around 7% with acceptable overall pregnancy and delivery rates. In Finland the increased use of single embryo transfer has reduced the proportion of multiple births. Finally, a good cryopreservation programme is essential to achieve a good cumulative delivery rate without multiple pregnancies.

Effect of laser-assisted hatching and necrotic blastomere removal on the development of vitrified-warmed four-cell mouse embryos

PURPOSE

To investigate the effect of laser-assisted hatching and necrotic blastomere removal on the development of vitrified-warmed mouse embryos.

METHODS

The vitrified-warmed four-cell stage mouse embryos were divided into five groups; vitrified intact with no laser-assisted hatching, vitrified intact with laser-assisted hatching, vitrified damaged with neither laser assisted hatching nor necrotic blastomere removal, vitrified damaged with laser-assisted hatching, and vitrified damaged with necrotic blastomere removal. Thereafter blastocyst formation, blastomere and apoptotic cell number within all groups were statistically compared.

RESULTS

The rate of blastocyst formation showed a significant improvement in the group vitrified intact with laser-assisted hatching. However, neither laser-assisted hatching nor necrotic blastomere removal can improve a delayed vitrified-warmed damaged embryos in term of blastocyst formation and total cell number. Nevertheless, apoptotic cell number was significantly reduced after application of both techniques.

CONCLUSIONS

Laser-assisted hatching can improve the development of vitrified-warmed intact four-cell stage mouse embryos, whereas necrotic blastomere removal has no significant effect on the development of vitrified-warmed four-cell stage damaged embryos.

Viability of frozen-thawed human embryos with one-two blastomeres lysis

OBJECTIVE

To assess the impact of one-two blastomeres lysis on the viability of thawed day 3 human embryos.

METHODS

A retrospective analysis was performed on 248 frozen-thawed embryo replacement cycles in which all embryos were frozen at day 3 at the seven-eight cell stage with <or=10% fragmentation.

RESULTS

Outcomes of transfer cycles with fully intact embryos (intact group) were compared with those in which all transferred embryos have lost one-two blastomeres (damage group). Comparable pregnancy rates (38.46% vs 38.64%), birth rates (34.62% vs 36.36%) and implantation rates (26.31% vs 26.25%) were obtained in intact and damage groups. These results were also not significantly different from mixed transfer cycles in which one intact embryo and one damaged embryo were transferred together.

CONCLUSION

The developmental potential of partially damaged cryopreserved human embryos with less than 25% cells loss is comparable to that of fully intact embryos. Presence of one-two lysed blastomeres in the thawed day 3 embryo does not appear to have a negative influence on the further development of the sibling intact cells.

Can cumulative pregnancy rates be increased by freezing and thawing single embryos?

OBJECTIVE

To evaluate the extent to which transfers of frozen single embryos increase cumulative pregnancy rates.

DESIGN

Retrospective analysis.

SETTING

IVF unit of a university hospital.

PATIENT(S)

Patients undergoing IVF cycles that were carried out from 2001 to 2005 (n = 1758). Patients were assigned to three groups according to the number of embryos frozen: group A, no cryopreservation; group B, a single embryo frozen; group C, several embryos frozen.

INTERVENTION(S)

Analysis of fresh ETs as a function of the number of embryos frozen and comparison outcomes for the thawing of a single embryo between subgroups B* (only one embryo frozen and thawed) and C* (last embryo of the cohort thawed).

MAIN OUTCOME MEASURE(S)

Implantation and pregnancy rates after fresh ETs and embryo survival and pregnancy rates after the transfer of a single thawed embryo.

RESULT(S)

The pregnancy rate per fresh ET increased significantly with the number of embryos frozen: 16.2% in group A, 21.4% in group B, and 26.5% in group C. For single thawed embryos, survival was higher in group C* (91.7%) than in group B* (72.6%). The pregnancy rate was also significantly higher in group C* (19.4% vs. 0%).

CONCLUSION(S)

The freezing of single embryos is of no benefit in cumulative pregnancy rates. ET strategies should therefore be reviewed.

Day 3 compared with day 2 cryopreservation does not affect embryo survival but improves the outcome of frozen-thawed embryo transfers

A retrospective study was performed to determine the differences in embryo survival and frozen-thawed embryo transfers outcome between cryopreservation performed on day 3 versus day 2. We conclude that freezing supernumerary embryos on day 3 provides similar thawing survival parameters, better implantation, pregnancy, and live-birth rates compared with day 2 cryopreservation.

A modified embryo cryopreservation method increases post-thaw survival with a concomitant increase in implantation

OBJECTIVE

To achieve maximum post-thaw survival of frozen embryos.

DESIGN

Historical controlled study.

SETTING

Hospital-based fertility center.

PATIENT(S)

One hundred forty-five patients whose embryos were frozen and thawed according to the standard method, and 56 patients whose embryos were frozen and thawed according to a modified method.

INTERVENTION(S)

Modifications were made to the various steps of cryopreservation: freezing and thawing solutions, loading of embryos into the straws, and warming rates.

MAIN OUTCOME MEASURE(S)

Post-thaw survival, implantation, and pregnancy rates.

RESULT(S)

With the modified method, 138 (93%) of the 149 embryos thawed for 56 patients survived freezing, and 79.8% had all their blastomeres intact, which is almost double the result obtained (41.8%) for patients whose embryos were thawed with the standard method. The implantation and pregnancy rates were also significantly higher with the modified method compared with the standard method.

CONCLUSION(S)

Greater post-thaw embryo survival was achieved, with a concomitant increase in implantation and pregnancy rates, by modifying the various steps in the standard cryopreservation methodology. This has important implications in IVF practice.

Developmental potential of fully intact and partially damaged cryopreserved embryos after laser-assisted removal of necrotic blastomeres and post-thaw culture selection

OBJECTIVE

Partially damaged frozen and thawed embryos are currently considered to have a lower viability than intact ones. This study was undertaken to compare the performance of intact frozen and thawed embryos with that of partially damaged embryos after removal of the necrotic blastomeres.

DESIGN

Observational clinical series.

SETTING

Private hospital.

PATIENT(S)

Three hundred twenty-six infertile couples undergoing frozen embryo transfer.

INTERVENTION(S)

Removal of necrotic blastomeres from frozen-thawed human embryos.

MAIN OUTCOME MEASURE(S)

Pregnancy and implantations rates.

RESULT(S)

Outcomes of frozen embryo transfer cycles in which all embryos were fully intact (group 1) were compared with those in which all embryos have lost 1-2 blastomeres (group 2) or 3-4 blastomeres (group 3). Laser-assisted hatching was performed in all embryos, and necrotic blastomeres were removed from partially damaged embryos on this occasion. Only embryos that resumed mitotic activity after thawing were transferred. Comparable clinical pregnancy rates (PR) (38.7%, 39.6%, and 29.4%), delivery rates (34.4%, 34.0%, and 29.4%), and implantation rates (21.6%, 21.4%, and 17.2%) were obtained in groups 1, 2, and 3, respectively.

CONCLUSION(S)

The developmental potential of partially damaged frozen and thawed embryos can be equivalent to fully survived embryos if the necrotic blastomeres are removed from the partially damaged embryos and only those of them that show post-thaw cleavage are selected for transfer.

Postthaw blastomere survival is predictive of the success of frozen?Thawed embryo transfer cycles

OBJECTIVE

To investigate the predictors of postthaw blastomere survival and the relationship of blastomere survival to the outcome of frozen-thawed embryo transfer (FET) cycles.

DESIGN

Retrospective study.

SETTING

An IVF unit in a tertiary care facility.

PATIENT(S)

Infertile women undergoing FET cycles with embryos cryopreserved on day 3 postinsemination.

INTERVENTION(S)

FET cycles.

MAIN OUTCOME MEASURE(S)

Embryo survival postthaw, pregnancy (PR), clinical pregnancy, and implantation rates.

RESULT(S)

A significant impact of postthaw blastomere survival on the outcome of FET cycles was noted. The thawed embryos in the low survival tertile resulted in significantly impaired implantation rate, clinical pregnancy rate, and PR compared to embryos in the high survival tertile. An inverse association was noted between serum P levels on the day of hCG administration and postthaw blastomere survival.

CONCLUSION(S)

We have demonstrated that postthaw blastomere survival is predictive of success of FET cycles. The relationship of poor postthaw embryo survival in the setting of elevated P is novel and not hitherto described.

Cumulative pregnancy rates after transfer of fresh and thawed embryos

Frozen-thawed embryo transfer is an effective procedure that allows further possibilities of pregnancy in addition to those obtained after the fresh in vitro fertilization (IVF). In our follow-up study we analysed all fresh embryo transfer procedures and every frozen-thawed embryo transfer performed from January 2000 to December 2001 evaluating the cumulative pregnancy rates. The study population was divided into two groups according to the female age: <38 years (group I) and >38 years (group II). All the best embryos were chosen for transfer and all the supernumerary good quality embryos were cryopreserved on the day of transfer. The embryos were then thawed and manipulated using a new technique. In group I, 527 patients (619 cycles) underwent fresh embryo transfer and in 232 of them (238 cycles) the embryos were frozen (44% per patients and 38.4% per cycle). In group II, 156 patients (193 cycles) underwent fresh embryo transfer and in 14 of them (15 cycles) the embryos were frozen (9% per patient and 7.8% per cycle). The pregnancy rate of group I patients that had their supernumerary embryos frozen (232 patients and 238 cycles) was 47.4% per cycle and 48.7% per patient whereas in the same population of group II patients (14 patients and 15 cycles) the clinical pregnancy rate was 35.7% per cycle and 38.5% per patients. The cumulative clinical pregnancy rate after transfer of fresh and thawed embryos was: group I, 74% per cycle and 76% per patients; group II, 42.8% per cycle and 46.1% per patient. Frozen-thawed embryo transfer is a cost-effective practice.

Effect of blastomere loss on the outcome of frozen embryo replacement cycles

OBJECTIVE

To assess the impact of survival of cryopreservation and thawing with all blastomeres intact on the outcome of frozen embryo replacement (FER) cycles.

DESIGN

Prospective observational study.

SETTING

University-affiliated tertiary referral assisted conception unit.

PATIENT(S)

The number of intact blastomeres before cryopreservation and after thawing was prospectively recorded in 1,687 cleavage-stage embryos thawed in 377 FER cycles. The cycles were categorized into two groups: group A (n = 184) included cycles in which all embryos transferred survived the cryopreservation and thawing process with all their original blastomeres intact; group B (n = 193) included cycles in which embryos transferred included at least one partially damaged embryo that has lost up to 50% of its original blastomere number.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Pregnancy and embryo implantation rates.

RESULT(S)

Groups A and B were comparable with respect to mean age at cryopreservation, mean number of oocytes retrieved and fertilized normally in the fresh cycle, and mean age at frozen transfer. No significant difference was found between the two groups with regard to mean number of frozen and thawed embryos per cycle and mean endometrial thickness reached before P supplementation. More embryos were transferred per cycle in group B than group A (2.4 +/- 0.6 vs. 2.1 +/- 0.6, respectively). However, the pregnancy and clinical pregnancy rates per cycle were significantly higher in group A than in group B (39.1% and 28.3% vs. 22.8% and 13.5%, respectively). The implantation rate was also higher in group A than in group B (17.3% vs. 8.1%, respectively).

CONCLUSION(S)

FER cycles in which all embryos transferred remained fully intact at thawing achieve a better outcome than those with at least one partially damaged embryo.

Laser-assisted removal of necrotic blastomeres from cryopreserved embryos that were partially damaged

OBJECTIVE

To examine whether the developmental potential of embryos that were partially damaged after freezing and thawing can be improved by removal of necrotic blastomeres before embryo transfer.

DESIGN

Prospective pilot study and observational clinical series.

SETTING

Private hospital.

PATIENT(S)

Two hundred thirty-five infertile couples undergoing frozen embryo transfer.

INTERVENTION(S)

Removal of necrotic blastomeres from frozen-thawed human embryos.

MAIN OUTCOME MEASURE(S)

Pregnancy and implantation rates.

RESULT(S)

Removal of necrotic blastomeres from partially damaged frozen-thawed embryos before transfer increased rates of pregnancy (45.7% vs. 17.1%), ongoing pregnancy (40.0% vs. 11.4%) and ongoing implantation (16.2% vs. 4.3%) compared with the control group, in which necrotic blastomeres were not removed. A similarly high implantation rate (16.7%) was seen a subsequent clinical series in which necrotic blastomeres were removed from all partially damaged embryos.

CONCLUSION(S)

The viability of partially damaged frozen-thawed embryos can be improved by removal of necrotic blastomeres before embryo transfer.

The influence of prefreeze growth rate and blastomere number on cryosurvival and subsequent implantation of human embryos

PURPOSE

To determine whether the relatively low implantation rate of cryopreserved Day 2 embryos with only 2 blastomeres can be increased as a consequence of increasing their blastomere content by extending the prefreeze culture time.

METHODS

Of a total of 3480 Day 2 embryos studied, 1921 (55.2%) had reached the 4-cell stage by 40 h postinsemination (FAST) and were transferred or cryopreserved. The remaining embryos that underwent subsequent cell division by 46 h (INTERMEDIATE; 18.3% of total) or 66 h (SLOW; 20.3% of total) were also cryopreserved whereas the 6.2% that remained arrested at 66 h were discarded. Thawed embryos from each category were assessed for survival, post-thaw cleavage, and implantation.

RESULTS

The proportion of thawed embryos that survived, the proportion of surviving embryos that underwent post-thaw cleavage, and the implantation rate of transferred embryos were all reduced in the slower growing cryopreserved embryos.

CONCLUSIONS

The growth rate, and not the number of blastomeres per se, is a critical factor in predicting the developmental potential of cryopreserved embryos.

Frozen pronuclear oocytes: advantages for the patient

Since the first reported pregnancy in a human being after a frozen/thawed eight cell stage preembryo, cryopreservation of preembryos has been integrated as an important element of assisted reproductive technologies (ART). The cryopreservation technique has brought several advantages to ART. It allows the transfer of a limited number of embryos in the collection cycle, thereby reducing the risk of multiple pregnancies, and the patients have a reservoir of excess embryos for additional transfers. This maximises the number of embryo transfers per oocyte retrieval, while at the same time increasing the cumulative pregnancy rate from a given treatment cycle. Also, the ability to freeze all the embryos obtained and transfer at a subsequent cycle is useful in the avoidance of hyperstimulation syndrome, or when factors that may jeopardize implantation are apparent. Freezing of oocytes in a pronuclear stage has a valuable role in the management of infertility. Supernumerary zygotes can be cryopreserved safely for future transfer, avoiding additional inconvenience for the patients. The freezing thawing technique does not have any adverse effects on oocytes fertilized microsurgically. Pronuclear stage oocytes eventually survive the cryopreservation procedure better, yielding after culture cleaved embryos appropriate for transfer, which could increase the implantation rate. We believe that the cryopreservation of cleaved embryos, which is problematic, can be safely replaced by this procedure. This is not only an advantage for society as a whole, but also for the people involved in the process, as there should be no ethical or moral conflict for the patients or for the laboratory staff about discarding this material.

The developmental potential of cryopreserved human embryos

Using rigorously matched non-frozen controls we have shown that cryopreservation does not alter the implantation potential of early cleavage stage (day 2) human embryos if no blastomere loss occurs. Thawed intact 4-cell embryos have a significantly higher implantation (fetal heart) rate (16.9%) than similar 2-cell embryos (7.2%). This difference is not due to blastomere number per se since increasing the cell number in frozen embryos by allowing an extended period in culture prior to freezing does not alter their intrinsic developmental potential. Blastomere loss, which occurred in almost half of all thawed embryos, is directly related to a reduction in developmental potential. We estimate that approximately 30% of the expected fresh embryo implantations are lost as a consequence of cryopreservation. Both preimplantation and peri-implantation losses may contribute to this outcome.

A quantitative analysis of the impact of cryopreservation on the implantation potential of human early cleavage stage embryos

The impact of cryopreservation on the implantation potential of early cleavage stage (day 2) embryos was assessed by analysing the outcome from > 5000 thawed embryos in relation to the outcome from a similar number of fresh embryos. Analysis of procedures in which all transferred embryos fulfilled equivalent defined criteria revealed no significant difference in the implantation rates (fetal hearts/100 embryos transferred) of fresh 4-cell embryos (16.6%) and fully intact thawed 4-cell embryos (16.9%). Although 2-cell embryos implanted at significantly lower rates, there was again no significant difference between fresh (6.5%) and fully intact thawed (7.2%) embryos. Similar analysis of all embryos (irrespective of cell number on day 2) demonstrated that the implantation potential of partially intact thawed embryos was related to the extent of blastomere loss with the implantation rate of embryos with 50% cell survival (5.4%) being approximately half the rate of fully intact embryos (11.3%). Combining the values obtained from 'pure' data for the implantation rates of embryos with defined levels of survival with their relative prevalence in the total population of thawed embryos gave a predicted number of implantations (441) which was similar to the observed outcome (463). This number was approximately 30% less than the number expected had the same embryos been transferred fresh (635). The results suggest that intact thawed embryos have the same implantation potential as equivalent fresh embryos and that the impact of cryopreservation is limited to blastomere loss which is directly related to loss of implantation potential. The observed frequency of blastomere loss results in a reduction of approximately 30% in the implantation potential of a population of embryos following cryopreservation.

Survival of cryopreservation and thawing with all blastomeres intact identifies multicell embryos with superior frozen embryo transfer outcome

OBJECTIVE

To assess the impact of survival of cryopreservation and thawing with all blastomeres intact on the outcome of multicell frozen ET.

DESIGN

Retrospective study.

SETTING

Academic assisted reproductive technology program.

PATIENT(S)

One hundred sixteen exclusively multicell frozen ETs in 78 patients.

INTERVENTION(S)

Frozen ET.

MAIN OUTCOME MEASURE(S)

Relation of embryonic blastomere survival to the outcome of frozen ET (i.e., pregnancy).

RESULT(S)

When at least one embryo survived with all blastomeres intact, the total pregnancy rate (biochemical, clinical, or delivered) was 37.7%, the clinical pregnancy rate was 24.6%, and the delivered pregnancy rate was 18.8%. When no embryo survived with all blastomeres intact, the corresponding rates were 10.6%, 8.5%, and 6.4%. The differences in the total pregnancy rate and the clinical pregnancy rate were statistically significant. The delivered pregnancy rates approached statistical significance.

CONCLUSION(S)

Multicell embryonic survival of cryopreservation and thawing with all blastomeres intact identifies embryos with superior developmental potential.

The presence of a sponsoring embryo in a batch of poor quality thawed embryos significantly increases pregnancy and implantation rate

OBJECTIVE

To evaluate quantitatively the effect of one good-quality (sponsoring) embryo in a batch of low-quality thawed embryos on the implantation and pregnancy rates (PR).

DESIGN

Retrospective analysis of data.

SETTING

Tertiary care center IVF clinic affiliated with a university medical school.

PATIENT(S)

Between March 1988 and April 1995, 392 IVF patients underwent a total of 440 thawing and ET cycles of 1,436 multicellular embryos.

MAIN OUTCOME MEASURE(S)

Implantation, clinical pregnancy, and multiple pregnancy rates.

RESULT(S)

In the absence of sponsoring embryos in the thawed batch of embryos, a PR of 9.8% with an implantation rate of 3.1% was achieved. In the presence of a single sponsoring embryo, the PR nearly doubled (18.2%), with a significantly higher implantation rate of 7.0%. Only singleton pregnancies were achieved in the absence of sponsoring embryos compared with 21.7% multiple pregnancies in the single sponsoring embryo group.

CONCLUSION(S)

The presence of a sponsoring embryo in a batch of poor quality thawed embryos is an important factor that significantly increased pregnancy and implantation rates. The optimal strategy for planning batches of multicellular frozen embryos is to include at least one sponsoring embryo in each batch when possible. We speculate that the sponsoring embryo may favorably influence the chances of low-quality embryos to undergo successful implantation.

Developmental potential of frozen-thawed human blastocysts

PURPOSE

To examine the possibility of freezing human embryos at late cleaved stages (morula or blastocyst stage), we cryopreserved human embryos 5 days (day 5) or 6 days (day 6) after insemination and investigated their developmental potential after thawing.

MATERIALS AND METHODS

One hundred nineteen morphologically good-quality human embryos from 43 women undergoing in vitro fertilization treatment between 1991 and 1992 were frozen using dimethylsulfoxide as a cryoprotectant. The embryos were cryopreserved for 5 to 30 months. After thawing they were then cultured in vitro for 24 hr to investigate their developmental potential. Survival rates and developmental rates were morphologically assessed after 24 hr of in vitro culture.

RESULTS

Developmental rates were significantly (P < 0.01 or P < 0.05) lower than survival rates at every developmental stage. There was no difference in total survival rates between embryos frozen 5 days after insemination (78.2%; 54/69) and embryos frozen 6 days after insemination (70.0%; 35/54). However, the developmental rates after 24 hr of culture was significantly (P < 0.05) lower for embryos frozen 6 days after insemination (6.0%; 3/50) than for embryos frozen 5 days after insemination (18.8%; 13/69). Only two embryos developed into fetuses after transfer into the uterus (1.7%; 2/119).

CONCLUSIONS

From the results, the developmental potential of frozen-thawed human blastocysts was found to be significantly reduced, even though the blastocysts were of morphologically good quality. Longer in vitro exposure of embryos appears to reduce their developmental potential.

Cryopreservation of human embryos

This chapter describes general cryobiological principles and the different methods for cryopreservation of supernumerary human embryos obtained after several procedures for medically assisted procreation. Different factors that influence the performance of freezing and thawing of human embryos are reviewed: the data from international and national surveys of results, the cryopreservation procedures, the stages of embryonic development, the morphological appearance of the cryopreserved embryos, the numbers of embryos transferred, the storage times of embryos in liquid nitrogen, the ovarian stimulation protocols in the IVF cycle and the replacement cycles of cryopreserved embryos. Cryopreservation of embryos circumvents the difficult problem of synchrony between the ovarian cycles of donor and acceptor patients in an oocyte donation programme.

Performance of cryopreserved pre-embryos obtained in in vitro fertilization cycles with or without a gonadotropin-releasing hormone agonist

OBJECTIVE

To evaluate the viability and potential for pregnancy of cryopreserved/thawed pre-embryos obtained after ovarian stimulation using gonadotropin-releasing hormone agonist (GnRH-a) adjunct therapy.

DESIGN

Retrospective clinical evaluation of all patients receiving a gonadotropin ovarian stimulation protocol (follicle-stimulating hormone/human menopausal gonadotropin [FSH/hMG]) with/without GnRH-a.

SETTING

Academic tertiary clinical care unit.

PATIENTS

Patients receiving leuprolide acetate (LA)/FSH/hMG (n = 136: LA in the luteal phase; long protocol) were compared with patients receiving FSH/hMG alone (n = 130) within the same time-frame in our program (April 1987 through October 1989).

INTERVENTIONS

All patients had both a cycle in which pre-embryos were transferred fresh and a cycle of thaw of cryopreserved pre-embryos (frozen at the pronuclear stage in a slow freeze-thaw protocol using 1,2 propanediol) transferred in monitored natural cycles.

MAIN OUTCOME MEASURES

Groups were similar in age, etiology of infertility, and cycle day 3 serum FSH levels; a significantly higher (P less than 0.001) number of preovulatory oocytes was recovered in the GnRH-a group. Both groups of patients were transferred an equal number of pre-embryos at the time of IVF. Cycles with frozen/thawed pre-embryos were evaluated based on the analysis of the three main variables that demonstrate cryopreservation efficiency: survival rate, implantation rate, and term pregnancy rate (PR).

RESULTS

Non-GnRH-a group (113 transfers): pre-embryo survival, 71.5%; PR/transfer, 24.7%; implantation rate, 16.0%; GnRH-a group (125 transfers): pre-embryo survival 71.6%; PR/transfer, 32.8%; implantation rate, 12.0% (no significant differences).

CONCLUSIONS

The use of GnRH-a produced pre-embryos of equal aptitude for development after cryopreservation at the pronuclear stage when compared with a similar gonadotropin stimulation treatment without GnRH-a.

Poor implantation of cryopreserved reinsemination-fertilized human embryos

OBJECTIVE

To investigate whether a poor rate of implantation after in vitro fertilization (IVF) was due to poor embryonic/endometrial synchrony during the original IVF cycle, we have cryopreserved reinseminated-fertilized embryos for later more synchronous replacement after thawing. The chance of implantation of fresh reinseminated fertilized human oocytes is approximately one tenth that of timely fertilized embryos. STUDY DESIGN AND DATA: Retrospective study of 35 original oocyte collections in which initial normal fertilization was 47.3% (129/273 oocytes), with 49.6% fertilization (67/135) upon reinsemination. Of these, 70 initially fertilized and 67 reinsemination-fertilized embryos were cryopreserved, and 50 initially fertilized and all 67 reinsemination-fertilized embryos were subsequently thawed with 72% and 63% cryosurvival, respectively, (not significant).

SETTING

Private infertility clinic.

RESULTS

In 11 cycles, 23 thawed initially fertilized embryos (group A) were replaced with a 21.7% implantation rate per embryo; in 10 cycles, 13 initially fertilized and 12 reinsemination-fertilized embryos (group B) were replaced together with an 8% implantation rate; finally, in 16 cycles, 30 reinsemination-fertilized embryos (group C) were replaced with a 3.3% implantation rate (group A versus group C: P = 0.076). Comparison of clinical pregnancies between these groups was significantly different (6/11 versus 1/16; P = 0.0427).

CONCLUSION

Reinsemination-fertilized embryos survive freezing as well as initially fertilized embryos, but better embryonic/endometrial synchrony does not improve chances of their implantation.