Does the developmental stage at freeze impact on clinical results post-thaw?

Fertility preservation practices for female oncofertility differ significantly across the USA: results of a survey of SREI members

PURPOSE

The field of oncofertility has maintained an important focus on improving access, yet standardized practices are lacking. To assess how female cancer patients are provided oncofertility care, we sought to determine provider-level differences and whether there are physician or practice characteristics that predict these variations.

METHODS

A cross-sectional survey was sent to SREI members. The survey included fifteen questions about physician practice characteristics and oncofertility cryopreservation protocols. Topics included ovarian stimulation protocols, fertilization techniques, stage of embryo cryopreservation, routine use of pre-implantation genetic testing for aneuploidy (PGT-A), and ovarian tissue cryopreservation (OTC). Statistical analyses assessed whether practice setting, geographic region, time in practice, and mandatory state insurance coverage had effects on cryopreservation protocols.

RESULTS

A total of 141 (17%) from diverse REI practice backgrounds completed the survey. The median number of new female oncofertility consults per year was 30 (range 1 to 300). Providers in academic settings treated more patients (median 40 vs. 15, p < 0.001). Providers in academic settings more often use gonadotropin-releasing hormone agonists (85% vs. 52%, p < 0.001) and perform OTC (41% vs. 4%, p < 0.001). Providers in academic practices were less likely to perform intracytoplasmic sperm injection in every cycle (37% vs. 55%, p = 0.032) and less likely to usually advise PGT-A (21% vs. 36%, p = 0.001). Mandated state insurance coverage had no effect on oncofertility practices.

CONCLUSION

Oncofertility practices vary among providers. Factors such as practice setting and region may affect the services provided. We do not yet know the best practices in oncofertility patients, and future research is needed.

Knockdown of pleiotrophin increases the risk of preeclampsia following vitrified-thawed embryo transfer

Preeclampsia (PE) in pregnancy is associated with vitrified-thawed embryo transfer. Pleiotrophin (PTN) is important in inflammation via its receptors. The aim of the present study was to determine the effect of PTN on the risk of PE following embryo transfer. An enzyme-linked immunosorbent assay was performed to determine the levels of tumor necrosis factor (TNF)-α and PTN in serum. The knockdown of PTN was conditionally induced by tamoxifen (tax) treatment. The tail-cuff method and Bradford assay were used to monitor blood pressure and the level of urine protein, respectively. The expression patterns of PTN, receptor protein tyrosine phosphatase β/ζ, (RPTPβ/ζ), syndecan-1 (SDC1), syndecan-3 (SDC3) and anaplastic lymphoma kinase (ALK) were determined by immunohistochemistry (IHC). Western blot analysis was performed to evaluate the expression level of PTN and its receptors. The risk of PE was elevated following embryo transfer in clinical and in the tax/PTN-/- group. It was found that the level of PTN increased when pregnancy progressed in normal conditions, however, the level of PTN was reduced in the PE mice. In addition, increases in TNF-α, blood pressure and urine protein were more marked in the PE mice that lacked PTN, compared with those in other PE mice. In addition, overlapping expression of PTN and its receptors in villous mesenchyme and fetal macrophages were identified using an IHC assay. However, the positive staining of PTN and its receptors was weaker or even absent in the PE mice. The protein level of RPTPβ/ζ was lower in the PE mice that lacked PTN than that in the other PE mice. The knockdown of PTN increased the risk of PE following vitrified-thawed embryo transfer, in which its receptors, particularly RPTPβ/ζ, may be involved.

Effect of laser-assisted multi-point zona thinning on development and hatching of cleavage embryos in mice

OBJECTIVE

This study aimed to examine the effect of laser-assisted zona thinning (LAZT) at one or four-points on the blastocyst formation and hatching process in mice with respect to female age.

METHODS

Eight-cell or morula embryos collected from superovulated C57BL female mice with different ages (6-11 and 28-31 weeks) were treated with LAZT at one-point (LAZT1) or four-points (LAZT4). The zona pellucida was thinned to more than 70% of its initial thickness by making two holes of 15-20 µm.

RESULTS

In the young mice, LAZT resulted in a significant increase in early hatching and hatching rates compared to the control group (p<0.05). However, in the old mice, LAZT significantly increased blastocyst formation as well as early hatching and hatching compared to the controls (p<0.05). These effects were more remarkable in LAZT4 than in LAZT1 and in aged mice than in young ones.

CONCLUSION

These results show that multi-point LAZT leads to a significant improvement of blastocyst formation and hatching in mice compared to controls.

Improvement of the vitrification method suppressing the disturbance of meiotic spindle and chromosome systems in mature oocytes

Vitrification method is widely used in oocyte cryopreservation for IVF but the birth rates are lower than that of the fresh oocyte. One of the known main reasons is structural instability of meiotic spindle and chromosome systems of mature oocyte. To get the best way for keeping competence of matured oocytes, we studied the best conditions for vitrification focused on equilibration times. The mature oocytes were underwent vitrification with current popular method and analyzed the survival rates, microtubule stability and DNA integrity. The survival rates of recovered oocyte are almost same between groups and are more than 93%. The structural configuration of meiotic spindle was well kept in 10 min equilibration group and the stability rate was almost same with that of control. The chromosomal breakdown was observed in all experimental groups, but the chromosomal stability was higher in 10 min equilibration group than the other groups. The 10 min equilibration group showed best condition compared with the other groups. Based on these results, the equilibration time is one of the key factors in successful keeping for competence of mature oocyte. Although, more fine analysis about the effects of physical stress on oocyte during vitrification is needed to define the optimal condition, it is suggested that the optimal equilibration time to get competent oocyte in mouse is 10 min. Information acquired this study may provide insight into intracellular structural events occurring in human oocytes after vitrification and application for cryopreservation of human oocyte.

Preliminary clinical outcome of novel strategy for the maximization of cumulative pregnancy rates per retrieval in normal responders

OBJECTIVE

We devised a novel strategy, a GnRH antagonist protocol with a GnRH agonist trigger followed by frozen-thawed blastocyst transfers with long zona dissection (LZD). The purpose of this study was to investigate the clinical outcomes of this new strategy according to age.

METHODS

Ninety women aged less than 35 (group A) and 32 women aged 35 to 39 (group B) underwent the GnRH antagonist protocol with a GnRH agonist trigger in order to obtain many oocytes and prevent early-onset ovarian hyperstimulation syndrome (OHSS). All oocytes were cultured to the blastocyst stage and all blastocysts grade 3BB or better were cryopreserved. Embryo transfers were only performed in freeze-thaw cycles to prevent late-onset OHSS and to overcome embryo-endometrium dyssynchrony. LZD was performed just after thawing to improve hatching and implantation rates.

RESULTS

The average numbers of retrieved oocytes and blastocysts grade 3BB or better were 12.8±5.5 and 4.4±2.6 in group A and 10.9±7.4 and 2.5±2.2 in group B, respectively, and OHSS did not occur in any of the women. Implantation rates were 46.7% in group A and 39.3% in group B. Cumulative clinical pregnancy rates per retrieval were 77.8% in group A and 62.5% in group B. Cumulative ongoing pregnancy rates per retrieval were 71.1% in group A and 53.1% in group B.

CONCLUSION

GnRH antagonist protocol with GnRH agonist trigger followed by frozen-thawed blastocyst transfers with LZD can generate many blastocysts without OHSS and maximize cumulative pregnancy rates per retrieval. This strategy is more effective in young women aged less than 35 than in women aged 35 to 39.

Cryopreservation of blastocysts is the most feasible strategy in good responder patients

OBJECTIVE

To assess on which day to cryopreserve and transfer thawed embryos in good-responder patients by comparing the cycle outcomes of day 3 transfers vs blastocysts formed through extended culture before or after cryopreservation.

DESIGN

Retrospective clinical study.

SETTING

Private IVF center.

PATIENT(S)

Frozen-thawed cycles (n = 2,531) who had ETs at day 3, 5, and 6 and post-thawed extended culture of day 3 until day 5 or 6.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Primary outcomes were implantation and delivery rates. Secondary outcomes were clinical pregnancy and miscarriage rates.

RESULT(S)

In thawing cycles, embryos developing to blastocysts on day 5 through extended culture before or after cryopreservation yielded higher rates of implantation (51.1% and 51.3%, respectively), clinical pregnancy (69.9% and 62.2%, respectively), and delivery per thawing cycle (56.7% and 51%, respectively) accompanied by lower miscarriage rates (15.2%, 16.4%, respectively) compared with day 3 transfers (28.3%, 55.3%, 42.5%, 20.1%, respectively). Late-developing embryos formed before or after cryopreservation resulted in compromised implantation (44.7% and 44.2%, respectively), clinical pregnancy (59.9% and 45.9%, respectively), delivery per thawing cycle (42.8% and 32.4%, respectively) and higher miscarriage rates (25.7% and 23.5%, respectively) than day 5 embryos.

CONCLUSION(S)

The feasible strategy in good responder patients appears to be the cryopreservation of blastocysts in the fresh cycle. Retardation in development results in a compromised outcome because of reduced inherent capacity of embryos.

Clinical pregnancy and live births after transfer of embryos vitrified on day 3

Human embryo vitrification is a promising new technology but clinical outcome data is needed to gauge its effectiveness and safety. While pregnancy and live-birth data is available for blastocyst vitrification, such information is lacking for human embryo vitrification at the 6- to 8-cell stage. The current work presents clinical and obstetric outcomes from the transfer of embryos vitrified on day 3 at the cleavage stage. A total of 270 transfers were performed. The clinical pregnancy and implantation rates for patients under 38 years of age (n=200) were 45% and 24%, respectively. Corresponding rates in patients 38-42 years old declined to 29% and 13% (n=70). Embryonic compaction and/or blastulation by the time of transfer were excellent prognostic indicators of a successful pregnancy outcome. Of the 66 deliveries, 12 (18.2%) were twin pregnancies and nine were preterm (13.6%). The mean birthweight for singletons was 3281+/-644 g, compared with 2506+/-549 g in the twin pregnancies. A total of 78 infants have been born with no major congenital malformations. These data attest to the efficacy and safety of the vitrification technique for cryopreservation of human embryos at the 6- to 8-cell stage.

Slow freezing, vitrification and ultra-rapid freezing of human embryos: a systematic review and meta-analysis

Embryo cryopreservation is an important aspect of assisted reproduction. Many methods have been described, but they have been poorly investigated in randomized trials, highlighting the need for a systematic review of the literature. Meticulous electronic/hand searches were performed to locate randomized trials (RCT) comparing embryo cryopreservation methods. Primary outcomes were clinical pregnancy rate (CPR) and incidence of congenital abnormalities. Secondary outcomes included live-birth (LBR), ongoing pregnancy (OPR), implantation (IR), and miscarriage (MR) rates. Data were extracted to allow for an intention-to-treat analysis and analysed using a random-effects model. Literature search revealed 11 RCT, of which five were excluded. The quality of the included studies was variable, but generally poor. There was a significantly higher CPR, OPR and IR with vitrification compared with slow freezing (odds ratio (OR)=1.55, 95% confidence interval (CI)=1.03-2.32, OR=1.82, 95% CI=1.04-3.20 and OR=1.49, 95% CI=1.03-2.15, respectively). In addition, there was a significantly lower CPR and OPR with embryo ultra-rapid freezing compared with slow freezing (OR=0.35, 95% CI=0.16-0.76 and OR=0.37, 95% CI=0.17-0.81, respectively). Vitrification is superior to slow freezing, which in turn is superior to ultra-rapid freezing. However, more well-designed and powered studies are needed to further corroborate these findings.

Vitrification of human early cavitating and deflated expanded blastocysts: clinical outcome of 474 cycles

PURPOSE

The present study was undertaken to evaluate and compare the post thaw survival, implantation and pregnancy rates of vitrified human early cavitating blastocysts with deflated expanded blastocysts.

MATERIAL AND METHODS

Supernumerary blastocysts were vitrified in 30% ethylene glycol-dimethyl sulphoxide based solution using cryoloop. Fully expanded blastocysts were deflated by gentle aspiration of the blastocoelic fluid using a micromanipulator until the cavity collapses prior to vitrification.

RESULTS

Of the 576 vitrified blastocysts, 545 (94.61%) survived thawing in the early cavitating blastocyst group which was significantly higher than deflated expanded blastocyst group, in which only 370 survived thawing out of 459 (80.62%). However, no significant difference was observed in implantation and pregnancy rates between early cavitating and deflated expanded blastocyst groups.

CONCLUSIONS

Early cavitating blastocyst would be the ideal stage for cryopreservation of human blastocysts as it has higher survival rate and avoids additional invasive procedures like deflation of the blastocoele.

Co-transfer of embryos derived from cryopreserved and fresh natural cycle oocytes: a pilot study

Italian legislation regarding reproductive medicine prohibits embryo storage while allowing cryopreservation of supernumerary oocytes. This study evaluated the effect of fresh oocytes obtained from natural unstimulated cycles on the clinical success rates derived from the use of frozen-thawed (FR-TH) oocytes obtained following ovarian stimulation. For 36 women, intracytoplasmic sperm injection was performed on FR-TH oocytes supplemented by a fresh oocyte, if available, derived from a natural cycle in which gonadotrophin-releasing hormone-antagonist was used for premature LH surge control. The retrieval rate of fresh oocytes was 61.1% and survival rate of FR-TH oocytes was 43.6%. The fertilization rate of fresh and FR-TH oocytes was 70% and 52.5%, respectively. Fifty embryos were transferred, 14 of them developed from fresh oocytes and 36 from FR-TH oocytes. Six pregnancies occurred in 10 cycles in which the embryos developed from fresh and FR-TH oocytes (pregnancy rate 60.0%) and two in 12 patients in whom the embryos were obtained from only FR-TH oocytes (pregnancy rate 16.7%) (P < 0.05). In summary, the data demonstrate that the transfer of embryos derived from oocytes cryopreserved following a previous ovarian stimulation and an embryo developed from a fresh one retrieved in natural cycle ensures an excellent clinical outcome.

Clinical efficiency of oocyte and embryo cryopreservation

The assessment of the standard for success of in vitro fertilization (IVF) treatment is an arduous task. Clinical efficiency and safety of a given procedure should represent fundamental tools for objective comparison. However, differences in patient populations, laboratory protocols, and expression of clinical data make the analysis of different studies and strategies very difficult. Formulation of the standard for success through the cumulative delivery rate per cycle of stimulation is a very attractive option because it includes the essential contribution of frozen embryos, which can represent 30-40% of all deliveries, while taking into account the need to minimize the proportion of pharmacological and surgical treatments. Embryo cryopreservation may be applied at different postinsemination stages. Larger and more detailed sets of data are available for day 2 embryo freezing, which allows cumulative delivery rates of 50-60% in good prognosis patients. In the last few years, novel freezing methods have improved the overall efficiency of oocyte cryopreservation. Especially in contexts afflicted by legal restrictions to embryo cryo- preservation, this form of preservation has started to have an impact on the IVF standard of success, generating cumulative pregnancy rates approaching 50%. Despite having been applied systematically by some IVF programs for only a few years, oocyte freezing already competes in efficiency with pronuclear-stage cryopreservation, and it does not appear unrealistic to predict that in the future it will challenge the dominance of embryo cryopreservation as the preferred form of conservation.

A randomized controlled study of human Day 3 embryo cryopreservation by slow freezing or vitrification: vitrification is associated with higher survival, metabolism and blastocyst formation

BACKGROUND

The aim of this study was to compare two methods of cryopreservation for the cleavage-stage human embryo: slow freezing and vitrification.

METHODS

A total of 466 Day 3 embryos, donated with consent, underwent cryopreservation by either slow freezing in straws or vitrification using the cryoloop. The vitrification procedure did not include dimethyl sulfoxide, but rather employed ethylene glycol and 1,2-propanediol as the cryoprotectants. Survival, embryonic metabolism and subsequent development to the blastocyst were used to determine the efficacy of the two procedures.

RESULTS

Significantly, more embryos survived the vitrification procedure (222/234, 94.8%) than slow freezing (206/232, 88.7%; P < 0.05). Consistent with this observation, pyruvate uptake was significantly greater in the vitrification group, reflecting a higher metabolic rate. Development to the blastocyst was also higher following vitrification (134/222, 60.3%) than following freezing (106/206, 49.5%; P < 0.05). In a separate cohort of 73 patients who had their supernumerary embryos cyropreserved with vitrification, the resulting implantation rate and clinical pregnancy rate were 30 and 49%, respectively.

CONCLUSIONS

Analysis of metabolism revealed that vitrification had less impact on the metabolic rate of the embryo than freezing, which was reflected in higher survival rate and subsequent development in vitro. Excellent pregnancy outcomes followed the warming and transfer of vitrified cleavage-stage embryos. These data provide further evidence that vitrification imparts less trauma to cells and is, therefore, a more effective means of cryopreserving the human embryo than conventional slow freezing. Clinicaltrials.gov identifier: NCT00608010.

Severe cytoplasmic abnormalities of the oocyte decrease cryosurvival and subsequent embryonic development of cryopreserved embryos

BACKGROUND

Abnormalities of oocyte morphology affect embryo quality and viability. Whether morphological abnormalities of the oocyte influence cryosurvival and further development of derived embryos is not known. The aim of this study was to compare cryosurvival and progression to the blastocyst stage of frozen-thawed embryos derived from normal and abnormal oocytes.

METHODS

A total of 5292 Grade 1 and 2 embryos from 964 women were frozen, thawed and subsequently cultured up to the blastocyst stage. The study was performed on excess embryos from patients who did not opt for cryopreservation. Cryosurvival, progression to the blastocyst stage and hatching were correlated with morphological characteristics of the oocytes that embryos were derived from.

RESULTS

Presence of a cytoplasmic abnormality of the oocyte significantly decreased cryosurvival. This detrimental effect was more pronounced in embryos derived from oocytes with vacuolar cytoplasm or with central granulation. Furthermore, these embryos did not have the potential to develop into good quality blastocysts or reach the hatching stage. On the other hand, presence of a single extracytoplasmic abnormality of the oocyte did not affect cryosurvival and the potential to develop into good quality blastocysts. Grade 2 embryos derived from oocytes with irregular shape or a large perivitelline space had decreased cryosurvival. However when these embryos survived cryopreservation, their potential to develop good quality blastocysts or to reach hatching stage was unaffected.

CONCLUSIONS

Embryos derived from oocytes with vacuolar cytoplasm or central granulation do not seem to bear the potential to develop good quality blastocysts or to reach hatching stage after cryopreservation. The presence of extracytoplasmic abnormalities alone does not affect blastocyst development despite decreasing cryosurvival.

Elective cryopreservation of all day 5 blastocysts is more effective than using day 6 blastocysts for improving pregnancy outcome in stimulated cycles

Aim:  To evaluate the efficacy of cryopreservation of all blastocysts for future transfers in stimulated cycles. Methods:  We carried out fresh blastocyst transfer cycles on day 5 (n = 290) or day 6 (n = 119) and thawed blastocyst transfer cycles that were frozen on day 5 (n = 136), day 6 (n = 71) or day 6 electively (n = 21). We retrospectively compared the clinical outcome of fresh blastocyst transfers with thawed blastocyst transfers according to the day of blastocyst transfer or freezing. Results:  The clinical implantation rates in women with stimulated cycles were significantly higher after the transfer of thawed blastocysts compared with the transfer of fresh blastocysts (day 5, P < 0.0005; day 6, P < 0.00005). Although the implantation rate of fresh day 6 transfer cycles was lower than that of elective day 6 frozen-thawed cycles, this difference was not statistically significant (P = 0.17). Conclusions:  Thawed blastocysts demonstrated a better potential for implantation when compared with fresh blastocysts in stimulated cycles. We concluded that elective cryopreservation of all blastocysts on day 5 is an effective option to improve the clinical outcome in stimulated cycles. Additionally, with cryopreservation of all day 6 blastocysts, the implantation rates of first embryo transfers may increase by allowing the best-quality blastocysts to be transferred in thawed cycles. (Reprod Med Biol 2008; 7: 75-83).

Current aspects of blastocyst cryopreservation

Cryopreservation of human gametes and embryos has become an essential part of assisted reproduction. Successful cryopreservation of human blastocysts is increasingly relevant as extended in-vitro culture of human embryos becomes more common, permitting routine use of blastocyst transfer in IVF programmes. This reduces the number of embryos transferred, thereby reducing multiple pregnancies and maximizing cumulative pregnancy rates per oocyte retrieval. The superiority of blastocyst freezing over earlier stage freezing in terms of implantation per thawed embryo transferred improves overall expectations for the cryopreservation programme. Therefore, a reliable procedure for the cryopreservation of blastocysts is needed because, after transfer, only a small number of supernumerary blastocysts are likely to be available for cryopreservation. Since the early 1980s, two common techniques have been used in cryopreservation: the conventional slow cooling method and the more recent rapid procedure known as vitrification. Vitrification has become an attractive alternative to slow freezing, since it appears to result in significantly higher survival and pregnancy rates. The aim of this review is to focus on the cryopreservation of human blastocysts using slow and rapid protocols and to assess the impact of the crypreservation protocol used on the survival, implantation and pregnancy rates.

Utilization of high-security straws for embryo freezing in an in vitro fertilization program: a prospective, randomized study

OBJECTIVE

To compare the outcome of frozen-thawed ET cycles where embryos had been stored in conventional versus ionomeric resin-based, high-security straws (HSSs).

DESIGN

Prospective, randomized study.

SETTING

Private assisted-reproduction unit.

PATIENT(S)

Three hundred and six freeze cycles, and 197 thaw cycles.

INTERVENTION(S)

Day 3 embryos (n = 1,268) were frozen, and 517 were thawed using HSSs. Alternately, day 3 embryos (n = 1,228) were frozen, and 505 were thawed using conventional straws.

MAIN OUTCOME MEASURE(S)

Cryosurvival, cleavage and morulae formation rates, and clinical pregnancy, implantation, and multiple pregnancy rates.

RESULT(S)

Although cycle characteristics did not show any differences, the cryosurvival rate was higher in the HSS group (94.7%) than in the conventional straw group (86%), as was the morulae formation rate (58.7% versus 42.7%). Despite a similar number of embryos being transferred, the clinical pregnancy rate (PR) was higher in the HSS group, but the difference lacked statistical significance (42.5% versus 31.2). Implantation rates (19.4% versus 11.4%) and multiple PRs (41.8% versus 16.6%) were significantly higher in the HSS group than in the conventional straw group.

CONCLUSION(S)

High-security straws are high effective in human embryo cryopreservation, because they provide higher cryosurvival and implantation rates, as well as a lower risk of cross-contamination compared to conventional straws.

Analysis of oocyte physiology to improve cryopreservation procedures

In contrast to the preimplantation mammalian embryo, it has been notoriously difficult to cryopreserve the metaphase II oocyte. The ability to store oocytes successfully at -196 degrees C has numerous practical and financial advantages, together with ethical considerations, and will positively impact animal breeding programs and assisted conception in the human. Differences in membrane permeability and in physiology are two main reasons why successful oocyte cryopreservation has remained elusive. It is proposed, therefore, that rather than relying on technologies already established for the preimplantation embryo, the development of cryopreservation techniques suitable for the mammalian oocyte needs to take into account the idiosyncratic physiology of this cell. Analysis of intracellular calcium, for example, has revealed that exposure to conventional permeating cryoprotectants, such as propanediol, ethylene glycol and DMSO, all independently result in an increase in calcium, which in turn has the potential to initiate oocyte activation, culminating in zona hardening. Quantification of the metabolome and proteome of the oocyte has revealed that whereas slow freezing has a dramatic effect on cell physiology, vitrification appears to have limited effect. This is plausibly achieved by the limited exposure to cryoprotectants. Analysis of meiotic spindle dynamics and embryo development following IVF, also indicate that vitrification is less traumatic than slow freezing, and therefore has the greatest potential for successful oocyte cryopreservation.

The CryoLoop facilitates re-vitrification of embryos at four successive stages of development without impairing embryo growth

BACKGROUND

Vitrification has been shown to be an effective method of cryopreservation, but little is known about re-vitrification of embryos. This study investigated the effect of re-vitrification on mouse embryo preimplantation development and viability post-transfer.

METHODS

Mouse embryos at the 1-cell stage were vitrified using the CryoLoop technique. Embryos were warmed and then re-vitrified successively at the 2-, 8-cell and blastocyst stages. The effects of multiple rounds of vitrification on development, differentiation and viability were assessed and compared with non-vitrified embryos.

RESULTS

Development to the 8-cell stage on day 3 and blastocyst on day 5 were not affected by re-vitrification. However, better hatching rates were observed in the non-vitrified control group. Total cell number and the number of cells allocated to the inner cell mass (ICM) were not different between treatments. The percentage of ICM development was also not different between treatments. Implantation rate and fetal weights were the same between treatments. However, overall there were fewer fetuses per embryo transferred in the re-vitrified group.

CONCLUSION

Re-vitrification of mouse embryos has minimal effect on preimplantation embryo development or implantation potential.

Frozen-thawed embryo transfer and live birth: Long-term follow-up after one oocyte retrieval

Frozen-thawed embryos accounted for 39% (249 of 639) of live births from 931 consecutive first oocyte retrievals after median follow-up of 6.5 years with consistent use of pronuclear-stage freezing and cleavage-stage transfer. Survival after thaw was 95% (2,129 of 2,247). Implantation and live birth rates per individual frozen-thawed embryo transfered were 22% (431 of 1,937) and 18% (346 of 1,937), respectively.

Cumulative pregnancy rates resulting from the use of fresh and frozen oocytes: 7 years' experience

Storing supernumerary embryos and transferring them later fully utilizes the reproductive potential of retrieved oocytes, allowing a significant increase in the overall number of pregnancies achieved from a single cycle of ovarian stimulation treatment. As an alternative to embryo cryopreservation, preservation of unfertilized oocytes has been proposed to maximize clinical outcome. This paper presents data concerning the cumulative pregnancy rate after use of fresh and cryopreserved oocytes. In 80 treatment cycles in which patients chose to have only a few fresh oocytes inseminated, 24 pregnancies were obtained (30.0%), with an implantation rate of 22.6%. After cryopreservation with the standard slow-cooling protocol, the survival, fertilization and cleavage rates of 918 frozen oocytes were 43.4, 51.5 and 86.0% respectively. A total of 14 frozen pregnancies were achieved, with pregnancy rate 19.2% per transfer and implantation rate 12.3%. The cumulative pregnancy rate was 47.5% per patient. Therefore, despite a low rate of oocyte post-thaw survival, it appears that oocyte storage appreciably improves the number of pregnancies per treatment cycle in cases in which only a minority of oocytes are destined for the fresh treatment. This outcome provides valuable information for appraising the chances of clinical success when the option of embryo cryopreservation is not available.

Cryopreservation of biopsied embryos at the blastocyst stage

BACKGROUND

The availability of an efficient cryopreservation program is especially important in the case of embryos that have undergone blastomere biopsy for PGD. Unfortunately, the freezing/thawing of biopsied embryos has given disappointing results when performed at the cleavage stage. In this study, embryos diagnosed as normal after PGD were grown to the blastocyst stage, frozen and thawed for successive frozen embryo transfer.

METHODS

A total of 34 patients performed a thawing cycle in which 47 blastocysts were thawed. The cryopreservation solutions were based on HEPES-buffered medium supplemented with human serum albumin (HSA), sucrose and 1,2-propanediol. The same protocol was applied to embryos from 88 IVF/ICSI patients, which underwent 92 thawing cycles with 150 thawed blastocysts.

RESULTS

The survival rate was similar in the two groups (53% after PGD and 58% in IVF/ICSI cycles), as well as the cumulative pregnancy rate per patient (59% after PGD versus 47% in IVF/ICSI cycles), despite a higher maternal age and a lower proportion of embryos available for transfer or cryopreservation in the PGD group.

CONCLUSIONS

Neither the survival rate nor the subsequent development and chances of implantation, differed between embryos frozen at the blastocyst stage following biopsy and those frozen intact.

Fads and foibles in ART: where is the evidence?

This commentary on the scientific basis of laboratory procedures in assisted conception discusses the origins of widespread discrepancies in 'standard' laboratory techniques experienced by patients and their embryos. The lack of direct evidence from clinical laboratory trials and the reasons for this will be highlighted using some examples drawn mainly from embryo culture. Inconsistencies and grey areas in the governance framework of this unique field could usefully be eliminated and attention focused on the need for a rational approach to procedural trials and pilot studies necessarily conducted in clinical laboratories. This may help progress towards a consensus on fundamental questions for which the evidence is currently lacking.

Are programmable freezers still needed in the embryo laboratory? Review on vitrification

The predictable answer to the provocative question of whether programmable freezers are still needed in the embryo laboratory is an even more provocative 'no'. However, such a radical statement needs strong support. Based on the extensive literature of the past 5 years, the authors collected arguments either supporting or contradicting their opinion. After an overview of the causes of cryoinjuries and strategies to eliminate them, the evolution of vitrification methods is discussed. Special attention is paid to the biosafety issues. The authors did not find any circumstance in oocyte or embryo cryopreservation where slow freezing offers considerable advantages compared with vitrification. In contrast, the overwhelming majority of published data prove that the latest vitrification methods are more efficient and reliable than any version of slow freezing. Application of the proper vitrification methods increases the efficiency of long-term storage of stem cells and opens new perspectives in cryopreservation of oocytes, both for IVF and somatic cell nuclear transfer. However, lack of support from regulatory authorities, and conservative approachs regarding novel techniques can slow down the implementation of vitrification. The opinion of the authors is that vitrification is the future of cryopreservation. The public have the final say in whether they want and allow this future to arrive.

Vitrification of mouse pronuclear oocytes with no direct liquid nitrogen contact

The ability to routinely cryopreserve human oocytes and embryos represents a significant advancement in the field of assisted reproductive technology. Although the method of slow freezing is commonly employed, research on the alternative technique of vitrification is promising. Vitrification involves incubation of the cell in a cryoprotectant rich solution, which permits a glass-like state to occur almost instantaneously in liquid nitrogen. A number of different techniques have been invented for holding oocytes and embryos in the cryoprotectant solution during rapid vitrification and subsequent storage. Most of these involve direct contact with liquid nitrogen. Recently, concerns have been raised regarding the sterility of such a method and the potential of viral contamination from the liquid nitrogen. The present study shows that the previously reported Cryoloop method can be used to vitrify and store embryos without direct liquid nitrogen contact (during vitrification and storage). When such vitrified embryos are warmed, they are capable of subsequent development comparable with non-vitrified embryos.

Removal of lysed blastomeres from frozen–thawed embryos improves implantation and pregnancy rates in frozen embryo transfer cycles

OBJECTIVE

To evaluate the effect of degenerated (lysed) blastomere removal on implantation and pregnancy rates in cleavage-stage cryo-embryo transfer (ET) cycles.

DESIGN

Randomized clinical trial.

SETTING

Private reproductive medical center.

PATIENT(S)

A total of 88 patients who received frozen-thawed ET, divided into two groups.

INTERVENTION(S)

Embryo freezing and thawing; opening of the zona pellucida and removal of cryodamaged blastomeres (in the study group), followed by same-day ET.

MAIN OUTCOME MEASURE(S)

Extent of survival of cleavage-stage embryos after the freeze-thaw procedure; embryo implantation and clinical pregnancies.

RESULT(S)

Oocyte number per patient, fertilization rate, embryo development rate (and quality), and freezing rates were similar in the two groups in the fresh cycle. In the control group, a total of 55 embryos (25%) of the 217 thawed remained fully intact, and 53 (26%) of the 207 in the study group remained intact. The average number of embryos transferred per group was similar (control, 3.4 +/- 0.9; study, 3.3 +/- 0.9). Implantation rates were 12% and 26% in the control and study groups, respectively. The clinical pregnancy rate was 23% in the control group and 64% in the study group when lysed cell removal was performed.

CONCLUSION(S)

The results show that pregnancy and implantation rates are higher in the study group; therefore, the removal of degenerated blastomeres may be beneficial to all patients who undergo cleavage-stage, frozen-thawed ET.

Clinical experiences of ICSI-ET thawing cycles with embryos cryopreserved at different developmental stages

PURPOSE

The aim of our study was to analyze factors including survival, implantation and pregnancy rate, patients' age and BMI, abortions and extra uterine pregnancies that might influence the outcome of ICSI-ET thawing cycles.

METHODS

A total of 147 cycles with embryos cryopreserved at different developmental stages were retrospectively evaluated.

RESULTS

No difference was found in the survival, implantation and pregnancy rates of embryos cryopreserved on Day 2-3 and 5. However, in the pregnant group significantly higher implantation rate was observed with Day 5 blastocysts then with Day 2 or 3 early embryos. We found no difference in the number of abortions and extra uterine pregnancies between fresh and frozen ICSI-ET cycles. Higher BMI was found in the pregnant than in the nonpregnant group. However, the age of patient had no effect on the results.

CONCLUSIONS

Developmental stage of embryo and patients' BMI influences the success of ICSI-ET thawing cycles.

Progressive elimination of microinjected trehalose during mouse embryonic development

Recently, sugars such as trehalose have been introduced into mammalian cells by overcoming the permeability barrier of cell membranes, and have provided improved tolerance against stresses associated with freezing and drying. However, the fate of the intracellular sugars has remained an open question. To address this issue, mouse oocytes were microinjected with 0.1 mol/l trehalose, and intracellular trehalose and glucose concentrations were determined during embryonic development using a high performance liquid chromatography and pulsed amperometric detection protocol. Trehalose was not detected in non-injected controls at any stage of development. In the microinjection group, the amount of intracellular trehalose progressively decreased as embryos developed. There was a corresponding increase in intracellular glucose concentration at the two-cell stage, suggesting cleavage of trehalose to two glucose molecules. In summary, this study presents a simple, highly sensitive protocol to determine intracellular sugars. The data reveal rapid elimination of microinjected trehalose during embryonic development. These findings have implications for designing osmolarity-optimized culture media for sugar-injected oocytes.

Slow controlled-rate freezing of sequentially cultured human blastocysts: an evaluation of two freezing strategies

BACKGROUND

To optimize blastocyst cryopreservation, the prerequisite is to develop a better understanding of factors that influence their survival and implantation potential. Therefore, the aim of the present work was to evaluate, retrospectively, the outcome of blastocyst cryopreservation in a day 2/3 fresh embryo transfer programme.

METHODS

Two different freezing strategies were compared: a first strategy (strategy A: 3007 blastocysts frozen) consisted of freezing those blastocysts that had at least a cavity; a second strategy (strategy B: 3831 blastocysts frozen) consisted of freezing only more advanced stage blastocysts with a good quality inner cell mass and trophectoderm. The outcome of cryopreservation, as related to the two different freezing strategies, was analysed. In addition, after freezing and thawing, we evaluated the influence of blastocyst developmental characteristics on immediate morphological survival and further development in vitro.

RESULTS

The immediate morphological survival after thawing was higher for early blastocysts as compared to advanced and hatching blastocysts. The further developmental potential in vitro of thawed blastocysts was higher for advanced and hatching blastocysts as compared to early blastocysts. As a result, the percentage of deliveries, calculated as a percentage of started thawing cycle, and the percentage of children born, calculated as a percentage of embryos transferred, was not different for strategies A and B.

CONCLUSION

The results clearly indicate that culture conditions and cryopreservation procedures of blastocysts need to be further improved.

Vitrification demonstrates significant improvement versus slow freezing of human blastocysts

Blastocyst culture has reduced the number of embryos transferred per cycle, whilst simultaneously creating new quandaries regarding supernumerary blastocyst cryopreservation. This retrospective study was undertaken to compare a slow freezing protocol to a vitrification protocol for cryopreservation of day 5 and day 6 human blastocysts. To demonstrate this, the survival, implantation rate and pregnancy rates were compared after thawing, assessment and embryo transfer of 86 consecutive day 5 and day 6 thawed blastocyst transfer cycles from January 1, 2002 to December 31, 2003. Seventy-one day 5 slow-frozen (SF) blastocysts were thawed and 59 embryos survived the thawing (83.1%). An average of 2.5 SF blastocysts was replaced per embryo transfer, resulting in a pregnancy rate of 16.7% (4/24). Concurrently, 41 vitrified (VIT) blastocysts were thawed and all 41 survived the thawing process (100%). An average of 2.0 VIT blastocysts was replaced per embryo transfer, resulting in a pregnancy rate of 50% (10/20). Survival, pregnancy and implantation rates of day 5 VIT blastocysts have significantly increased (P < 0.01, P < 0.02 and P < 0.01 respectively) over day 5 SF blastocysts. A similar trend was observed with day 6 blastocysts.

Reduction of high order multiples in frozen embryo transfers

The aim of this study was to determine if blastocyst frozen embryo transfers are able to reduce the potential for the rate of high order multiples (HOM) (>2 fetal sacs) without affecting the overall pregnancy and implantation potential. Group A included all frozen blastocyst transfers prior to 1 January 2002. Group B included all frozen blastocyst transfers between 1 January 2002 and 12 December 2003. There was no significant difference for survival for the two time periods (79 versus 80%). A significantly (P<0.05) lower number of embryos were transferred in group B (1.9) compared with group A (2.8). There was a significant (P<0.05) reduction of (HOM) from 31 to 3% for groups A and B respectively. Ongoing pregnancy rates for group A resulted in 52% of 25 embryo transfers and 41% of 75 embryo transfers in group B (not significant). Reducing the number of embryos transferred between groups A and B did not significantly impact implantation rates. It is concluded that blastocyst freezing is effective for overall survival, pregnancy and implantation while reducing the rate of high order multiples.

Criteria to assess human oocyte quality after cryopreservation

Oocyte cryopreservation certainly represents one of the most attractive developments in the field of assisted reproduction, with the aim of preserving female fertility and circumventing the ethical and legal drawbacks associated with embryo freezing. Despite the achievement of the first pregnancy from frozen oocytes dating back as early as 1987, since then fewer than 150 pregnancies have been reported. Over a long period of time, application of oocyte storage on a large scale has been prevented by various factors, namely poor post-thaw survival. Fertilization rates remained low even after the introduction of intracytoplasmic sperm injection. Modifications of slow-freezing protocols, mainly based on the increase of the concentration of sucrose used as non-penetrating cryoprotectant (CPA) and the replacement of sodium with choline, appear to have decisively improved survival rates to over 80%. Investigations at the cellular level on thawed oocytes are largely lacking. Fertilization rates have also benefited from protocol modifications, reaching values indistinguishable from those normally obtained with fresh material. Vitrification protocols have also been tested, giving rise to improvements whose reproducibility is still uncertain. Data on the dynamics of fertilization and preimplantation development of embryos derived from frozen oocytes are extremely scarce. At the moment, clinical efficiency of oocyte cryopreservation cannot be precisely assessed because of the lack of controlled studies, although it appears to be considerably lower than that achieved with embryo freezing. In summary, encouraging advances have been made in the field of oocyte cryopreservation, but presently no protocol can ensure standards of success and safety comparable to those guaranteed by embryo storage.

High pregnancy rates can be achieved after freezing and thawing human blastocysts

OBJECTIVE

To examine the results of a 3-year trial using blastocyst cryopreservation to limit multiple pregnancy and optimize overall pregnancy per cycle.

DESIGN

Retrospective clinical evaluation of pregnancy rates after freezing and thawing human blastocysts.

SETTING

Tertiary-care academic center.

PATIENT(S)

Seven hundred fifty-three different patients treated in 783 IVF cycles with blastocysts frozen from July 2000 to June 2003.

INTERVENTION(S)

Two thousand, two hundred fifty-nine blastocysts were frozen in cycles in which only blastocysts were cryopreserved (cycles with pronuclear stage oocytes or pre-embryos also cryopreserved were excluded from the analysis). Of these, 628 (27.6%) were thawed in 218 cycles.

MAIN OUTCOME MEASURE(S)

Pregnancy rate per cycle with thaw.

RESULT(S)

Four hundred seventy-nine (76.3%) blastocysts survived thawing, and 440 (92.0%) were transferred after exhibiting evidence of survival (most commonly, blastocoele reexpansion). In cycles with a thaw, 211 (96.8%) of 218 underwent intrauterine transfer. An average of 2.09 blastocysts was transferred per replacement. One hundred twenty-five (59.2%) clinical pregnancies were established, which included 23 sets of twins and 5 triplet gestations. Two sets of monozygotic twins were identified after the replacement of a single thawed blastocyst (1.6%). The age of the patient at the time of cryopreservation (<37 years) was an important factor in the establishment of clinical and ongoing pregnancy. The mode of ovarian stimulation, replacement method, and whether blastocysts were frozen on day 5 or day 6 of development did not demonstrate clinical significance.

CONCLUSION(S)

Cryopreserved and thawed blastocysts demonstrated a similar potential for implantation when compared with fresh pre-embryos on day 3. On the basis of these results, the blastocyst stage of development appears to be optimal for clinical freeze-thaw trials.

Multiple displacement amplification on single cell and possible PGD applications

Multiple displacement amplification (MDA) is a technique used in the amplification of very low amounts of DNA and reported to yield large quantities of high-quality DNA. We used MDA to amplify the whole genome directly from a single cell. The most common techniques used in PGD are PCR and fluorescent in-situ hybridization (FISH). There are many limitations to these techniques including, the number of chromosomes diagnosed for FISH or the quality of DNA issued from a single cell PCR. This report shows, for the first time, use of MDA for single cell whole genome amplification. A total of 16 short tandem repeats (STRs) were amplified successfully with a similar pattern to the genomic DNA. Furthermore, allelic drop out (ADO) derived from MDA was assessed in 40 single cells by analysing (i) heterozygosity for a known beta globin mutation (IVSI-5 C-G) and by studying (ii) the heterozygous loci present in the STRs. ADO turned out to be 10.25% for the beta globin gene sequencing and 5% for the fluorescent PCR analysis of STRs. Moreover, the amplification accuracy of MDA permitted the detection of trisomy 21 on a single cell using comparative genome hybridization-array. Altogether, these data suggest that MDA can be used for single cell molecular karyotyping and the diagnosis of any single gene disorder in PGD.

Single embryo transfer and IVF/ICSI outcome: a balanced appraisal

This review considers the value of single embryo transfer (SET) to prevent multiple pregnancies (MP) after IVF/ICSI. The incidence of MP (twins and higher order pregnancies) after IVF/ICSI is much higher (approximately 30%) than after natural conception (approximately 1%). Approximately half of all the neonates are multiples. The obstetric, neonatal and long-term consequences for the health of these children are enormous and costs incurred extremely high. Judicious SET is the only method to decrease this epidemic of iatrogenic multiple gestations. Clinical trials have shown that programmes with >50% of SET maintain high overall ongoing pregnancy rates ( approximately 30% per started cycle) while reducing the MP rate to <10%. Experience with SET remains largely European although the need to reduce MP is accepted worldwide. An important issue is how to select patients suitable for SET and embryos with a high putative implantation potential. The typical patient suitable for SET is young (aged <36 years) and in her first or second IVF/ICSI trial. Embryo selection is performed using one or a combination of embryo characteristics. Available evidence suggests that, for the overall population, day 3 and day 5 selection yield similar results but better than zygote selection results. Prospective studies correlating embryo characteristics with documented implantation potential, utilizing databases of individual embryos, are needed. The application of SET should be supported by other measures: reimbursement of IVF/ICSI (earned back by reducing costs), optimized cryopreservation to augment cumulative pregnancy rates per oocyte harvest and a standardized format for reporting results. To make SET the standard of care in the appropriate target group, there is a need for more clinical studies, for intensive counselling of patients, and for an increased sense of responsibility in patients, health care providers and health insurers.

Determining the most optimal stage for embryo cryopreservation

The objective of this study was to compare cleaved embryo and blastocyst freezing to determine the optimal time for embryo cryopreservation. A retrospective analysis was carried out for all frozen embryo transfer cycles where transfer occurred on either day 3 or day 5. Blastocyst freezing increased the ongoing pregnancy, implantation and survival rates post-thaw as compared with cleaved embryo thaws. There was no difference in ongoing pregnancies for fresh and frozen-thawed blastocyst transfers (59% versus 62%) respectively. Additionally, fresh blastocyst transfers had a higher proportion of supernumerary embryos cryopreserved than did day 3 transfers (38% versus 26%). Blastocyst freezing is a viable option for handling patient's supernumerary embryos while optimizing pregnancy outcomes per oocyte retrieval.

Vitrification versus programmable rate freezing of late stage murine embryos: a randomized comparison prior to application in clinical IVF

A prospective randomized trial was performed to compare post-thaw development of murine blastocysts following programmable rate freezing and two methods of vitrification. Frozen 2-cell murine embryos (n = 429) thawed and cultured for 48 h, were randomly allocated by stage of development into four groups: control (not refrozen), programmable rate freezing (PR) in 0.25 ml straws, vitrification in flexible micropipettes by immersion in super-cooled (VSC) liquid nitrogen (LN2), and vitrification in flexible micropipettes by immersion in LN2 (VLN). Survival, developmental stage progression, presence or absence of an inner cell mass (ICM), and cell counts were recorded 24 h post-thaw. All measured outcomes were different between embryos from the control group and all freezing methods. Controlled-rate freezing resulted in the lowest total cell counts and fewest embryos with a distinct ICM. A higher percentage of embryos survived 24 h post-thaw, progressed to more advanced developmental stages and had higher total cell counts after VLN compared with PR. Moreover, fewer embryos, frozen by either PR or VSC, contained a detectable ICM compared with VLN. These data demonstrate that vitrification may be a better method for freezing murine blastocysts than PR, and may prove to be a superior method for freezing human blastocysts.

Cryopreservation as a tool to reduce multiple birth

The potential role of embryo cryopreservation from the point of view of prevention of multiple pregnancies is analysed. Cryopreservation is an unavoidable option in stimulated IVF/intracytoplasmic sperm injection (ICSI), but at the same time an underestimated tool in the prevention of twins. There is a need for an evaluation system not only of the cryotechnology process per se, but also of the true augmenting effect of cryopreservation on the total reproductive potential of a single oocyte harvest. Only cryopregnancies occurring after an unsuccessful fresh cycle (possibly followed by one or more unsuccessful freeze-thaw cycles with embryos from the same harvest) truly reflect the augmentation potential of cryopreservation. This potential is greater than generally thought. First, the efficacy of cryopreservation is suboptimal with survival rates between 30 and 70%. Second, if single-embryo transfer were applied in a much larger proportion of cycles than is presently the case, more embryos would be available for cryopreservation, resulting in more and more successful freeze-thaw cycles. In the future, the combination of elective single-embryo transfer with an optimized cryopreservation programme is likely to become the standard of care for routine IVF/ICSI treatment.

Modified vitrification and cooling of human pronuclear oocytes: efficacy and effect on ultrastructure

The efficacy of cryopreservation by direct plunging into liquid nitrogen (vitrification) of human pronuclear oocytes using open pulled straws with a super-finely pulled tip, as well as the ultrastructural changes caused by cooling and vitrification, were evaluated. Clinical and electron microscopic studies of cooled and vitrified oocytes were performed. Oocytes were cooled to 4 degrees C in the presence and absence of cryoprotectants, vitrified, warmed, cultured and transferred. Abnormally fertilized oocytes were examined by electron microscopy. Vitrified and warmed 2-pronuclear oocytes showed 71.1% survival rate and 83.3% developmental rate. One- and 3-pronuclear oocytes, after cooling without cryoprotectants (presumably non-viable), showed progressive swelling of mitochondrial smooth endoplasmic reticulum (SER). After vitrification, oocytes (presumably viable) showed the formation of large SER vesicles associated with mitochondria. The described protocol of vitrification of human pronuclear oocytes was shown to be effective in producing pregnancy. Normal ultrastructure after undergoing the described vitrification protocol was confirmed.