Resumption of mitosis during post-thaw culture: a key parameter in selecting the right embryos for transfer

Impact of Post-Thaw Incubation Time of Frozen Embryos on Clinical Pregnancy Rate

Background

Vitrification of embryos following a single-controlled ovarian stimulation has been the strategy practised now in many in vitro fertilisation clinics to minimise the risk of early ovarian hyper stimulation syndrome, to reduce multiple pregnancy rates and to improve cumulative pregnancy rates. In recent years, advances in vitrification techniques and improved culture conditions have led to good post-thaw embryo survival rates, thereby increasing pregnancy rates of frozen embryo transfer (FET) cycles.

Aim

The aim of this study was to analyse the effect of post-thaw incubation time of frozen embryos on the clinical pregnancy rates (CPRs) of frozen embryo transfer (FET) cycles.

Settings and Design

This was a retrospective, comparative study done at a teaching hospital in assisted reproductive treatment.

Materials and Methods

Three hundred and ten FET cycles were analysed, of which 125 had day 2 freezing and 185 had day 3 freezing. Depending upon the day of thawing and day of transfer, FET cycles were divided into six groups: Group 1 (day 2 thawing and day 3 transfer), Group 2 (day 2 thawing and day 4 transfer), Group 3 (day 2 thawing and day 5 transfer), Group 4 (day 3 thawing and day 3 transfer), Group 5 (day 3 thawing and day 4 transfer) and Group 6 (day 3 thawing and day 5 transfer).

Statistical Analysis Used

Statistical analysis was performed using version 14 R software version 4.0.1 (2020-06-06) (R foundation for Statistical Computing, Vienna, Austria). A P < 0.05 is taken as significant.

Results

The CPR of Group 4 was 42.4% which was more than that of the other groups but it did not reach statistical significance.

Conclusions

Short incubation time of 2-4 h is as effective as an extended incubation time in terms of CPRs of FET cycles.

A proof of concept for a deep learning system that can aid embryologists in predicting blastocyst survival after thaw

The ability to understand whether embryos survive the thaw process is crucial to transferring competent embryos that can lead to pregnancy. The objective of this study was to develop a proof of concept deep learning model capable of assisting embryologist assessment of survival of thawed blastocysts prior to embryo transfer. A deep learning model was developed using 652 labeled time-lapse videos of freeze-thaw blastocysts. The model was evaluated against and along embryologists on a test set of 99 freeze-thaw blastocysts, using images obtained at 0.5 h increments from 0 to 3 h post-thaw. The model achieved AUCs of 0.869 (95% CI 0.789, 0.934) and 0.807 (95% CI 0.717, 0.886) and the embryologists achieved average AUCs of 0.829 (95% CI 0.747, 0.896) and 0.850 (95% CI 0.773, 0.908) at 2 h and 3 h, respectively. Combining embryologist predictions with model predictions resulted in a significant increase in AUC of 0.051 (95% CI 0.021, 0.083) at 2 h, and an equivalent increase in AUC of 0.010 (95% CI -0.018, 0.037) at 3 h. This study suggests that a deep learning model can predict in vitro blastocyst survival after thaw in aneuploid embryos. After correlation with clinical outcomes of transferred embryos, this model may help embryologists ascertain which embryos may have failed to survive the thaw process and increase the likelihood of pregnancy by preventing the transfer of non-viable embryos.

Extended culture of cleavage embryo to blastocyst embryo is among the good predictors of successful outcome in vitrified-thawed ICSI cycles

Background

Previous studies showed that top-quality embryo transfer (ET), number of transferred embryos, endometrial preparation with natural cycles or mild stimulation, and female BMI independently affected the outcome in frozen-thawed ET. However, the effect of culturing thawed cleavage embryos to blastocyst stage on the outcome was not sufficiently elucidated. Our objective is to evaluate the role of this extended culturing as predictor of cycle outcome in vitrified-thawed ICSI cycles.

Materials and methods

One thousand forty-two consecutive cycles of vitrified-thawed ET done in a single IVF unit [Mansoura Integrated Fertility Centre (MIFC)] were reviewed during a period from 2014 to 2017. Endometrial preparation methods were natural, stimulation by antiestrogen and/or gonadotropins, or replacement using sequential estradiol (E2) and progesterone (P4). The primary outcome was the clinical pregnancy rate while the secondary outcome was the chemical and ongoing pregnancy rate.

Results

Overall clinical pregnancy rate (CPR) is 298/1042 is 28.5%, chemical pregnancy rate (326/1042) 31.3%, and ongoing pregnancy rate (167/615) 27.2%. Comparing clinically pregnant (n = 298) and non-pregnant (n = 744) showed, respectively, the following: age 28.76 ± 5.0, 28.85 ± 5.18 (p = 0.8); BMI 31.06 ± 5.9, 32.45 ± 5.9 (p = 0.002); infertility duration 4.17 ± 3.2, 4.6 ± 3.5 (p = 0.038); endometrial thickness 10.82 ± 1.6, 10.13 ± 2.06 (p = 0.0001); and no. of ET 3.35 ± 1.5, 3.12 ± 1.60 (p = 0.035). The clinical pregnancy rate when vitrification was done on cleavage embryos was 198/502 (39.4%), and when vitrification done on blastocyst stage 100/ 536 (18.7%) (P < 0.0001); endometrial preparation: natural 72/240(29.1%), stimulated 204/680 (30.0%) replacement 17/90 (18.8%) (p = 0.09); extended culture of cleavage embryos to blastocyst stage: clinical pregnancy rate 116/194 (59.7%) chemical pregnancy rate 125/194 (64.1%), ongoing pregnancy rate 87/165 (52.7%) and non extended culture clinical pregnancy rate 182/848 (21.4%), chemical pregnancy rate 201/848 (23.7%), and ongoing pregnancy rate 80/450 (17.7%) (P < 0.0001).

Conclusion

Top-quality ET, number of transferred embryos and extended culture of cleavage embryos to blastocyst stage, cleavage embryos but not infertility duration, BMI, endometrial thickness, or hCG trigger of ovulation independently predict successful outcome in frozen cycle ET and extended culture of cleavage embryos significantly improved clinical and chemical and ongoing pregnancy rates.

Effect of post‐warming culture time on the live birth rate after frozen embryo transfer

Purpose

Methods

Results

Conclusions

Post-thaw culture has no beneficial effect on frozen embryos transfer outcomes comparing to same embryonal age non-cultured frozen-thawed embryos

PURPOSE

To assess the impact of post-thawing embryo culture on frozen embryo transfer (FET) outcomes.

METHODS

A retrospective cohort study including 678 consecutive FET cycles performed between the years 2004 and 2017 was conducted. Patients older than 45 years old were excluded. FET cycles were stratified as follows: (1) two-day (2d) embryos thawed and cultured to three-day (3d) versus 3d embryos thawed and transferred; (2) 2d or 3d embryos thawed and cultured to blastocysts versus blastocysts thawed and transferred. A p-value <.05 was considered statistically significant.

RESULTS

Maternal age, BMI, smoking, and basal FSH of the 2d and 3d cultured embryo group (n = 110) and the 3d non-cultured embryo group (n = 189) were comparable. Endometrium preparation protocols and the achieved endometrial thickness did not differ between groups. Pregnancy rate, implantation rate, clinical pregnancy, live birth rate, abortions, multiple pregnancies, perinatal outcomes, and birth weight were comparable.The 2d and 3d embryos cultured to blastocyst (n = 41) compared to non-cultured blastocyst (n = 338) showed that the non-cultured blastocyst patients had higher smoking rates and longer follicular phase. Endometrial thickness was comparable. The 2d and 3d embryos cultured to blastocyst stage had higher multiple pregnancies rate compared to the blastocyst non-cultured group, whereas pregnancy rate, implantation rate, live birth rate, miscarriages, perinatal outcomes, and birth weight were comparable.

CONCLUSION

We could not demonstrate that the post-thaw culture had a significant impact on the outcome of FET cycles.

The impact of post-warming culture duration on clinical outcomes of vitrified-warmed single blastocyst transfer cycles

OBJECTIVE

The objective of the study was to compare the effects of long-term and short-term embryo culture to assess whether there is a correlation between culture duration and clinical outcomes.

METHODS

Embryos were divided into two study groups depending on whether their post-warming culture period was long-term (20-24 hours) or short-term (2-4 hours). Embryo morphology was analyzed with a time-lapse monitoring device to estimate the appropriate timing and parameters for evaluating embryos with high implantation potency in both groups. Propensity score matching was performed to adjust the confounding factors across groups. The grades of embryos and blastoceles, morphokinetic parameters, implantation rate, and ongoing pregnancy rate were compared.

RESULTS

No significant differences were observed in the implantation rate or ongoing pregnancy rate between the two groups (long-term culture group vs. short-term culture group: 56.3% vs. 67.9%, p=0.182; 47.3% vs. 53.6%, p=0.513). After warming, there were more expanded and hatching/hatched blastocysts in the long-term culture group than in the short-term culture group, but there was no significant between-group difference in embryo grade. Regarding pregnancy outcomes, the time to complete blastocyst re-expansion after warming is shorter in women who became pregnant than in those who did not in both culture groups (long-term: 2.19±0.63 vs. 4.11±0.81 hours, p=0.003; short-term: 1.17±0.29 vs. 1.94±0.76 hours, p=0.018, respectively).

CONCLUSION

The outcomes of short-term culture and long-term culture were not significantly different in vitrified-warmed blastocyst transfer. Regardless of the post-warming culture time, the degree of blastocyst re-expansion 3-4 hours after warming is an important marker for embryo selection.

Do different culture intervals (2 × 24 hours) after thaw of cleavage stage embryos affect pregnancy rates? A randomized controlled trial

The aim of the study was to evaluate whether selecting embryos for transfer after prolonged culture after thaw (18-24 h) has better pregnancy rates than selecting embryos for transfer after short culture after thaw (2-5 h). We performed a double-blinded, randomized, controlled trial, evaluating 388 patients submitted to ART treatment who had embryos frozen on day-2 and subsequently transferred. All patients received the same endometrial priming with estradiol valerate followed by vaginal progesterone. Patients were randomized for Frozen embryo transfer 2-5 h after thaw (Group D2) or 18-24 h after thaw (Group D2/D3). The main Outcome Measure was ongoing pregnancy rate (OPR) at 20 weeks' gestation per embryo transfer. A total of 179 patients had embryos transferred 2-5 h after thaw and 209 patients had embryos transferred 18-24 h after thaw. The mean age in group D2 was 36 ± 4.4 and 36 ± 5.4 in group D2/D3. Ongoing pregnancy rate was 28% and 33.5% (p = 0.2) for groups D2 and D2/D3, respectively. These results suggest that increasing the culture time of embryos in one day to improve selection before transfer does not increase ongoing pregnancy rate. CLINICAL TRIAL REGISTRATION NUMBER: NCT03381001.

Associations of post-warming embryo or blastocyst development with clinical pregnancy in vitrified embryo or blastocyst transfer cycles

Objective

To investigate whether the degree of post-warming embryo or blastocyst development is associated with clinical pregnancy in vitrified embryo or blastocyst transfer cycles.

Methods

Ninety-six vitrified cleavage-stage embryos and 58 vitrified blastocyst transfer cycles were selected. All transfer cycles were performed from February 2011 to March 2019, and all vitrified embryos or blastocysts were warmed from 4 PM to 6 PM and then transferred the next morning from 9 AM to 10 AM. The scores of the cleavage-stage embryos and blastocysts were assessed at warming and at transfer using the modified Steer method and the Gardner method, respectively. The mean embryo or blastocyst score, score of the single top-quality embryo or blastocyst, and the difference in the score between warming and transfer were compared between nonpregnant and pregnant women.

Results

In the cleavage-stage embryo transfer cycles, both the top-quality embryo score at transfer and the difference in the score between warming and transfer were significantly associated with clinical pregnancy. A top-quality embryo score at transfer of ≥60.0 (area under the curve [AUC], 0.673; 95% confidence interval [CI], 0.531–0.815) and a difference in the score between warming and transfer of ≥23.0 (AUC, 0.675; 95% CI, 0.514–0.835) were significant predictors of clinical pregnancy. In blastocyst transfer cycles, the top-quality blastocyst score at transfer was the only significant factor associated with clinical pregnancy. A top-quality blastocyst score at transfer of ≥38.3 was a significant predictor of clinical pregnancy (AUC, 0.666; 95% CI, 0.525–0.807).

Conclusion

The top-quality embryo score at transfer and the degree of post-warming embryo development were associated with clinical pregnancy in vitrified cleavage-stage embryo transfer cycles. In vitrified blastocyst transfer cycles, the top-quality blastocyst score at transfer was the only significant factor affecting clinical pregnancy.

Antifreeze protein from Anatolia polita (ApAFP914) improved outcome of vitrified in vitro sheep embryos

Embryo cryopreservation is an important tool to preserve endangered species. As a cryoprotectant for mouse oocytes, antifreeze protein from Anatolica polita (ApAFP914) has demonstrated utility. In the present study, the effects of controlled slow freezing and vitrification methods on the survival rate of sheep oocytes fertilized in vitro after freezing-thawing were compared. Different ApAFP914 concentrations were added to the vitrification liquid for exploring the effect of antifreeze protein on the warmed embryos. The results showed that the survival and hatching rates of in vitro derived embryos were significantly higher than that of the slow freezing method. Furthermore, among the cryopreserved embryos at different developmental stages, the survival and hatching rates of the expanded blastocyst were significantly higher than those of the blastocysts, early blastocysts and morula. The survival and the hatching rates of the fast-growing embryos were both significantly higher than that of the slow-growing embryos. Additionally, treatment of ApAFP914 (5-30 μg/mL) did not increase the freezing efficiency of the 6-6.5 d embryos. However, addition of 10 μg/mL of ApAFP914 significantly increased the hatching rate of slow-growing embryos. In conclusion, our study suggests that the vitrification is better than the slow freezing method for the conservation of in vitro sheep embryos, and supplementation of ApAFP914 (10 μg/mL) significantly increased the hatching rate of slow-growing embryos after cryopreservation.

Chapter 9 Slow Freezing and Thawing of Human Cleavage Stage Embryos

The ability to store human embryos in a viable state at very low temperatures has been critical to the evolution of responsible practice in clinical Assisted Reproductive Technology (ART). It has encouraged a reduction in the frequency of simultaneous multiple embryo transfer and thereby reduced the risks associated with multiple pregnancy while maintaining high cumulative pregnancy rates from single oocyte collection cycles. In this chapter, we describe a simple slow freezing procedure for human early cleavage stage embryos that results in a high proportion of post-thaw embryos surviving and retaining their implantation potential.

Time-lapse imaging of cleavage divisions in embryo quality assessment

In vitro fertilization (IVF) is one of the most important procedures for treating infertility. As several embryos are usually produced in a single IVF cycle, it is crucial to select only the most viable ones for transfer to the patient. Morphokinetics, i.e. analysis of the dynamics of cleavage divisions and processes such as compaction and cavitation, has provided both biologists and clinicians with a new set of data regarding embryonic behaviour during preimplantation development and its association with embryo quality. In the current review, we focus on biological significance of morphokinetic parameters and show how they can be used to predict a reproductive outcome. We also explain the statistics behind the predictive algorithms and discuss the future perspectives of morphokinetics.

The total pregnancy potential per oocyte aspiration after assisted reproduction-in how many cycles are biologically competent oocytes available?

PURPOSE

While stimulation of women prior to assisted reproduction is associated with increased success rates, the total biological pregnancy potential per stimulation cycle is rarely assessed.

METHODS

Retrospective sequential cohort study of the cumulative live birth rate in 1148 first IVF/ICSI-cycles and 5-year follow up of frozen embryo replacement (FER) cycles were used. Oocyte number, number of embryos transferred, and cryopreserved/thawed and transferred embryos in a FER cycle were registered for all patients. Children per oocyte and per transferred embryo and percentage of cycles with births were calculated.

RESULTS

We obtained 9529 oocytes. Embryos (2507) were transferred in either fresh or FER cycles, resulting in 422 births and 474 live born children. Median age of the women was 32.5 years (range 20-41.5 years). In total, 34.3 % of all cycles ended with a live birth while in 65.7 % of the cycles, no oocytes were capable of developing into a child. The average number of oocytes needed per live born child after transfer of fresh and thawed embryos was 20 as only 5.0 % of oocytes aspirated in the first IVF/ICSI cycle had the competence to develop into a child.

CONCLUSIONS

In our setting, overall 5.0 % of the oocytes in a first cycle were biologically competent and in around 2/3 of all cycles, none of the oocytes had the potential to result in the birth of a child.

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.

Vitrification can modify embryo cleavage stage after warming. Should we change endometrial preparation?

PURPOSE

Studies have shown that embryo metabolism and cell cleavage after warming vitrified embryos is faster than after thawing frozen embryos. We study vitrified embryo transfer (VET) results depending on the developmental stage of warmed embryos and the duration of progesterone treatment before embryo transfer.

METHODS

We designed a prospective study, patients were randomized in two groups, starting progesterone three (D + 3) or four days (D + 4) before embryo transfer. We recruited 88 patients with embryos vitrified on day 3.

RESULTS

We didn't find statitistical differences in pregnancy rate when we transferred embryos in D + 3 vs D + 4 (38.2 % vs 40.5 % p ≥ 0.05). The day after warming, 54.6 % of embryos had developed to morula or early blastocyst, 32.4 % to cleavage stage and 13 % didn't cleave. Transfers were with morula/blastocysts stage embryos (52.1 %; n:37), cleavage stage embryos (18.3 %; n:13) or mixed (29.6 %; n:21). Implantation rate was significantly higher in morula/blastocyst stage than in cleavage stage or mixed transfers (44 %, 22 % and 16.3 %; p = 0.011). Pregnancy and implantation rates were significantly higher in morula/blastocyst transfers on D + 4 than on D + 3 (68.7 % and 64.7 % vs 33.3 %, and 33.3 %, p = 0.033 and p = 0.034).

CONCLUSIONS

Our findings suggest that a majority of embryos will develop to morula/blastocyst stage after warming. VET results with morula/blastocysts, and after four days of progesterone supplementation, are better than with cleavage stage embryos.

Influence of post-thaw culture on the developmental potential of human frozen embryos

PURPOSE

Apart from freezing/thawing related cryodamage, several additional factors have been identified as major players in the reduction of success rates after frozen embryo transfers. The post-thaw culture is particularly relevant as it may amplify environmental influences over a stressed embryo. In the present study the influence of the post-thaw culture duration on the implantation and developmental potential of cleavage stage embryos was evaluated.

METHODS

In this retrospective evaluation, that spanned an 8-year period, 631 frozen-thawed embryos were allocated to one of two study groups, depending on their post-thaw culture period: 1) the long (18-24 h), or 2) the short (2-5 h) culture group. Groups were compared regarding implantation rate and live birth rate per embryo transferred. This comparison was corrected for the most common confounding factors such as maternal age at oocyte pick-up, number of transferred embryos, developmental day at freezing, blastomere survival after thawing, catheter used for transfer and year of procedure.

RESULTS

Implantation and live birth rate per embryo transferred were inversely related to the duration of the post-thaw culture, as diminishing this period significantly increased both rates. Moreover, no advantage could be found for a long post-thaw culture period, even for embryos with observed mitotic activity.

CONCLUSION

This retrospective analysis indicates that a short post-thaw culture period is associated with higher implantation and live birth rates per embryo. This study supports selection of frozen-thawed embryos strictly based on blastomere cryosurvival and raises the hypothesis that environmental factors may have an important role on embryo implantation and developmental potential during post-thaw culture.

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.

Study on the Imprinting Status of Insulin-Like Growth Factor II (IGF-II) Gene in Villus during 6-10 Gestational Weeks

Objective. To compare the difference of imprinting status of insulin-like growth factor II (IGF-II) gene in villus between normal embryo development group and abnormal embryo development group and to investigate the relationship between karyotype and the imprinting status of IGF-II gene. Methods. A total of 85 pregnant women with singleton pregnancy were divided into two groups: one with abnormal embryo development (n = 38) and the other with normal embryo development (n = 47). Apa I polymorphism of IGF-II gene in chorionic villus was assayed with reverse transcriptase polymerase chain reaction (RT-PCR) and restriction fragment length polymorphism (RFLP). The relationship between chromosomal abnormal karyotype and IGF-II gene imprinting status was analyzed by primary cell culture and G-banding chromosomal karyotype analysis. Results. IGF-II imprinting loss rate was higher in the abnormal embryo development group than the normal embryo development group (44.7% versus 31.6%), but without significant difference (P > .05). The percentage of abnormal chromosomes of chorionic villus in the abnormal embryo development group was 42.5%, in which IGF-II imprinting loss rate reached 64.7%. No abnormal karyotypes were found in the normal embryo development group. However, there was significant difference in IGF-II imprinting loss rate between two groups (P > .05). Conclusion. During weeks 6–10 of gestation, abnormal embryonic development is correlated with chromosomal abnormalities. The imprinting status of IGF-II gene played important roles in embryonic development, and imprinting loss might be related to chromosomal abnormalities.

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.

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.

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.

Resumption of mitosis in frozen-thawed embryos is not related to the chromosomal constitution

OBJECTIVE

To study the relation between the resumption of mitosis after thaw and chromosomal constitution in frozen-thawed embryos. In addition, to evaluate the correlation among the three parameters of resumption of mitosis after thaw, postthaw blastomere loss, and multinucleation.

DESIGN

Frozen-thawed embryos were morphologically evaluated at thaw and after 24 hours of culture. Then, fluorescence in situ hybridization (FISH) analysis, including enumeration of 13 chromosomes, was performed by using a combination of peptide nucleic acid and DNA probes.

SETTING

In vitro fertilization laboratory.

PATIENT(S)

Forty IVF and/or intracytoplasmic sperm injection patients.

INTERVENTION(S)

Embryo thawing, morphological evaluation, and fluorescence in situ hybridization analysis for aneuploidy screening.

MAIN OUTCOME MEASURE(S)

Resumption of mitosis, blastomere loss, multinucleation, and chromosome enumeration.

RESULT(S)

No difference was observed in the chromosomal constitution of embryos with and without resumption of mitosis. Neither was the postthaw blastomere loss connected to the chromosomal constitution. The resumption of mitosis was not associated with postthaw loss of blastomeres or with multinuclearity.

CONCLUSION(S)

Resumption of mitosis and blastomere loss of frozen-thawed embryos is not related to chromosome aberrations in the embryo. Further, the resumption of mitosis is not correlated with multinucleation. However, the high incidence of multinucleated embryos after thawing indicates that the freezing and thawing procedure may affect this condition.

Human oocyte cryopreservation

The clinical role of oocyte cryopreservation in assisted reproduction, as an adjunct to sperm and embryo cryopreservation, has been comparatively slow to evolve as a consequence of theoretical concerns related to efficacy and safety. Basic biological studies in the 1990's alleviated many of these concerns leading to more widespread adoption of the technology. While a number of babies were born from the approach validated in the 1990's, its perceived clinical inefficiency led to the search for improved methods. Introduction of elevated dehydrating sucrose concentrations during cryopreservation increased survival and fertilization rates, but there is no well-controlled evidence of improved clinical outcome. Similarly, the use of sodium-depleted cryopreservation media has not been demonstrated to increase clinical efficiency. More recently, and in the absence of basic biological studies addressing safety issues, the application of vitrification techniques to human oocytes has resulted in reports of a number of live births. The small number of babies born from clinical oocyte cryopreservation and the paucity of well-controlled studies currently preclude valid comparisons between approaches. Legal restrictions on the ability to select embryos from cryopreserved oocytes in Italy, where many of the available reports originate, also obscure attempts to assess oocyte cryopreservation objectively.

Relationships between timing of syngamy, female age and implantation potential in human invitro-fertilised oocytes

Although early developmental markers are frequently used to select embryos for transfer in human assisted reproduction, their value as independent predictors of outcome is often unclear. In this study, the value of using early syngamy and first cleavage as predictors of implantation potential of Day 2 embryos was investigated by examining their interrelationships with subsequent development, female age and implantation. Implantation rates were higher when syngamy occurred before 23–24 h post insemination even when all embryos analysed were transferred 42 h post insemination at the 4-cell stage (25.8 v. 11.9% for the later syngamy group; P < 0.01). Although there was a significant (r = 0.682; P < 0.001) relationship between earlier entry into syngamy and female age, earlier syngamy was still associated with a significantly higher implantation rate in Day 2 embryos with four blastomeres in women under 36 years of age (31.4 v. 15.4% for the later syngamy group; P < 0.05). The ability of timing of syngamy to predict implantation independent of other variables was confirmed by multiple logistic regression analysis. Although related to both subsequent embryo development and female age, early entry into syngamy is a predictor of implantation potential independent of both correlates in human Day 2 in vitro-fertilised embryos.

Embryonic factors affecting outcome from single cryopreserved embryo transfer

Multiple pregnancy minimization by single embryo transfer is becoming more prevalent, but is less common in the case of cryopreserved embryos. This study defines embryonic characteristics in single cryopreserved embryo transfers associated with success rates equivalent to those achieved when transferring two cryopreserved embryos. In a retrospective analysis of 6916 cryopreserved day-2 embryo transfer procedures, transfer of two cryopreserved embryos resulted in higher clinical pregnancy rates when compared with transfer of a single thawed embryo but was also associated with elevated multiple pregnancy rates (26.7% in women under 36). Optimal outcome (implantation rate of 30.9%) from single cryopreserved embryo transfer (SCET) in women under 36 was associated with cryopreservation at the 4-cell stage, loss of fewer than two blastomeres and subsequent cleavage of at least two surviving blastomeres. In comparison, transfer of two cryopreserved embryos in women under 36 resulted in pregnancy and implantation rates of 25.5 and 16.1% respectively. Interestingly, in cryopreserved 4-cell stage embryos, loss of a single blastomere did not reduce implantation potential and cleavage of only a single post-thaw blastomere was not indicative of increased implantation potential. Establishment of these critical thresholds provides a rational basis for SCET.

How should the clinical efficiency of oocyte cryopreservation be measured?

Clinical application of oocyte cryopreservation may be in the context of fertility preservation for women about to undergo cytotoxic therapies or may be as an alternative to embryo cryopreservation in routine assisted reproduction. The clinical efficiency of oocyte cryopreservation will be a consequence of the cumulative impact of pre-freeze oocyte quality, postthaw survival and subcellular effects of cryopreservation protocols, which impact on early embryo quality and post-transfer viability, together with the degree of selection which is applied to the available biological material. Any valid assessment must include reference to all the above aspects, particularly when comparing cryopreserved oocytes with non-frozen controls or cryopreserved embryos. Cumulative pregnancy rates from oocyte collections may provide the most relevant index of success. Survival of human oocytes cryopreserved using current methodology is similar to that achieved with early-cleavage-stage embryos. Although evidence suggests that developmental potential may be compromised when current oocyte cryopreservation protocols are applied, there is a paucity of rigorously controlled studies in the literature.

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.

Towards defining parameters for a successful single embryo transfer in frozen cycles

BACKGROUND

Twin pregnancies in IVF should be avoided by transferring embryos one at a time, even for frozen cycles. In this study, we investigated the effect of blastomere lysis and cleavage in singleton frozen embryo transfer (sFET) cycles. Outcomes were compared with the transfer of two embryos in frozen transfer cycles (dFET).

METHODS

A retrospective analysis was performed on 891 FET cycles, involving 404 sFET and 487 dFET cycles.

RESULTS

Overall, in sFET cycles, the pregnancy and implantation rates were 8.9 and 8.7%. When blastomere lysis was more than 25% but no greater than 50%, the pregnancy and implantation rates were 3.2%. If blastomere lysis was greater than 50% there were no pregnancies. If blastomere lysis was less than 25%, but with no cleavage, the pregnancy and implantation rates were 4.1%. The results significantly improved (P = 0.007) in the group with less than 25% lysis, when cleavage occurred. The pregnancy and implantation rates for this group were 17.3 and 16.6%. This was not significantly different from unselected two embryo transfers (22 and 12.7%,P = 0.2 and 0.19, respectively). There were 21 twins with dFET (19.6% of pregnancies) and none in sFET.

CONCLUSION

Both blastomere lysis and cleavage affect the outcome in sFET. To avoid the risk of twins, sFET should be considered when the embryo shows less than 25% blastomere lysis and at least one blastomere cleaves.

Parameters predicting the implantation rate of thawed IVF/ICSI embryos: a retrospective study

Single embryo transfer is becoming increasingly popular in IVF/ICSI. More IVF/ICSI cycles therefore include freezing of high quality embryos, and the cumulative effect of such cycles becomes more important. To improve the results obtained using frozen-thawed embryos, the predictive value of embryo and patient characteristics was analysed retrospectively. Excess embryos were frozen on day 2 according to routine procedures and thawed 24 h before transfer. The women were either treated with oestradiol/progesterone, or the transfer took place after a natural cycle. Of 1777 embryos thawed, 1360 survived (survival rate 76.5%). In the 410 transfer cycles, 819 embryos were transferred, giving 109 positive serum HCG tests and 69 clinical pregnancies. The implantation rate was 10.4%. Five parameters were positively related to implantation: (i) four or more cells at the freezing time (day 2); (ii) resumption of mitosis after thawing; (iii) more than six cells at transfer (day 3); (iv) assisted hatching and (v) child in a previous fresh cycle. The relative predictive value of these parameters may be a guideline for the selection of embryos used for transfer. Assisted hatching may become routine in freeze-thaw cycles if its utility is confirmed in subsequent studies.

Comparison of growth rates of fresh and frozen-thawed embryos according to chromosomal status

PURPOSE

To report a comparison of growth rates between fresh and frozen-thawed embryos on day 3 and 4 according to chromosomal status during PGD.

METHODS

Embryos were biopsied on day 3, fluorescent in situ hybridization performed for aneuploidy detection and growth rates monitored.

RESULTS

Based on 241 egg pick up-PGD and 133 frozen embryo transfer-PGD cycles. The development rate of embryos despite their chromosomal status was similar on day 3, however, overall, fresh embryos showed a significantly improved development (> or =6 cell stage; 85.7%) compared to frozen embryos (77.0%; p < 0.003). On day 4 fresh embryos showed accelerated development and further developmental improvements were associated with chromosomal normality (56.1% normal vs. 42.2% aneuploid; p < 0.004).

CONCLUSIONS

Cryopreservation slows embryo development regardless of the chromosomal status. However, chromosomal status did not influence the chance of embryo implantation which was the same for fresh and thawed embryos.

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.

Single embryo transfer is an option in frozen embryo transfer

BACKGROUND

A good strategy to decrease multiple pregnancy rate in assisted reproduction technology (ART) is the use of single embryo transfer (SET).

METHODS

This retrospective study analysed 1647 frozen embryo transfers carried out during 1998-2003 in Helsinki University Central Hospital; of these, 872 were double embryo transfers (DETs) and 775 SETs. The SET group included 140 (18.1%) elective SETs (eSETs).

RESULTS

The yearly rate of SETs in frozen cycles increased from 28 to 66%. Overall, the clinical pregnancy rate per frozen embryo transfer was 30.7% and the delivery rate 22.6%. The delivery rate was significantly higher in DET cryocycles than in SET cryocycles (25.7 versus 19.2%, respectively; P < 0.01). In DET cryocycles, the multiple delivery rate was 21.9%, 10 times higher than that observed in cryocycles with SET (2.0%) (P < 0.0001). When eSET was applied, no difference in delivery rate was observed when compared with cryocycles with DET (28.6 and 25.7%, respectively).

CONCLUSIONS

SET can be used in frozen cycles to reduce multiple delivery rates.

Porcine embryo development and fragmentation and their relation to apoptotic markers: a cinematographic and confocal laser scanning microscopic study

Porcine embryo selection prior to transfer is mainly influenced by morphological criteria. However, the relationship between embryonic morphology, developmental potential and cell death by apoptosis in porcine embryos is still unclear. The aim of this study was to establish embryo quality parameters for in vivo fertilised porcine embryos based on timing of development in vitro, embryo morphology and the presence of apoptosis. The kinetics of development and morphological parameters were investigated in a time-lapse cinematographic experiment. Possible links between embryo morphology and apoptosis were examined via a confocal laser scanning experiment, analysing nuclear changes, annexin V and terminal dUTP nick-end labelling. The timing of early cleavages was firmly linked to embryo developmental competence in vitro. Attainment of at least the 5-cell stage before 77 h post insemination and attainment of the morula stage before 102 h post insemination significantly increased the odds for reaching the early blastocyst stage. Overall, a negative effect of fragmentation percentage and fragmentation pattern on subsequent embryonic development was observed, but the developmental potential of embryos experiencing slight fragmentation (0–5%) was not different from embryos without fragmentation. Correlations detected between developmental arrest and fragmentation, and fragmentation and apoptosis were 0.60 and 0.87 (P < 0.05) respectively. Only a minority of the embryos arrested between the 1- and 4-cell stage displayed biochemical characteristics of apoptosis. Consequently, a significant correlation (0.57) between developmental arrest and apoptosis could only be established for embryos arrested after embryonic genome activation.

Middle Eastern masculinities in the age of new reproductive technologies: male infertility and stigma in Egypt and Lebanon

Worldwide, male infertility contributes to more than half of all cases of childlessness; yet, it is a reproductive health problem that is poorly studied and understood. This article examines the problem of male infertility in two Middle Eastern locales, Cairo, Egypt, and Beirut, Lebanon, where men may be at increased risk of male infertility because of environmental and behavioral factors. It is argued that male infertility may be particularly problematic for Middle Eastern men in their pronatalist societies; there, both virility and fertility are typically tied to manhood. Thus, male infertility is a potentially emasculating condition, surrounded by secrecy and stigma. Furthermore, the new reproductive technology called intracytoplasmic sperm injection (ICSI), designed specifically to overcome male infertility, may paradoxically create additional layers of stigma and secrecy, due to the complex moral and marital dilemmas associated with Islamic restrictions on third-party donation of gametes.

Survival and developmental potential of stored human early cleavage stage embryos

Human early cleavage stage embryos which survive cryopreservation and thawing fully intact demonstrate similar developmental potential to equivalent non frozen embryos when returned to the in vivo environment, whereas blastomere loss is directly related to the loss of potential for subsequent implantation in thawed embryos. This suggests that blastomere lysis during freezing and thawing does not occur preferentially in non viable blastomeres. Prefreeze growth rate rather than prefreeze blastomere number per se correlates with the developmental potential of stored embryos. When blastomere loss occurs as a consequence of cryopreservation, development of thawed early cleavage stage embryos to the blastocyst stage in vitro is impaired and the resultant blastocysts have a reduced total cell content. Blastomere loss is more prevalent in embryos which have been biopsied for preimplantation genetic diagnosis but this increased sensitivity can be circumvented by modification of the standard cryopreservation protocol.

Heparin-binding epidermal growth factor and its receptor ErbB4 mediate implantation of the human blastocyst

The mechanisms that mediate implantation of the human embryo remain poorly understood and represent a fundamental problem in reproductive biology. Candidate molecules that mediate and facilitate implantation have been identified in animal studies, and include heparin binding epidermal growth factor. Here we demonstrate a potential function for the transmembrane form of heparin-binding epidermal growth factor in mediating blastocyst attachment to the endometrium, in two different novel in vitro models for human implantation. Furthermore, we demonstrate specific localisation of the heparin-binding epidermal growth factor receptor ErbB4, on the surface of the trophectoderm in peri-implantation human blastocysts. Our data lead the way for further dissection of the molecular mechanisms of implantation of the human embryo, and have implications for infertility, in vitro fertilization and contraception.

Aromatase inhibition for ovarian stimulation: future avenues for infertility management

Ovarian stimulation is applied during infertility management either alone or in conjunction with intrauterine insemination and assisted reproductive technologies. At the present time, the two main medications used for ovarian stimulation include an oral antiestrogen, clomiphene citrate, and injectable gonadotropins. In spite of the high ovulation rate with the use of clomiphene citrate, the pregnancy rate is much lower. In clomiphene citrate failures, gonadotropin injections have generally been used as the next treatment option. Treatment with gonadotropins is difficult to control and characteristically associated with increased risk of severe ovarian hyperstimulation syndrome and high multiple pregnancies. Therefore, an effective oral treatment that could be used without risk of hyperstimulation and with minimal monitoring is the preferred therapy. We hypothesize that aromatase inhibitors can be administered early in the follicular phase to induce ovulation by releasing the hypothalamus or pituitary from estrogen negative feedback. Based on this hypothesis, we have reported the success of aromatase inhibitors in induction and augmentation of ovulation in addition to improving ovarian response to gonadotropin stimulation. Moreover, there are other potential applications for aromatase inhibitors in infertility management, including improving implantation in assisted reproduction and in-vitro maturation.

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.

Expression of Fas and Fas ligand mRNA in rat and human preimplantation embryos

The Fas-Fas ligand (L) system is one of the major signalling pathways to induce apoptosis in various cells and tissues. The aim of this study was to investigate the expression of the Fas-Fas L system in rat and human oocytes and preimplantation embryos. We determined the expression of Fas and Fas L mRNA of rat oocytes and embryos up to the blastocyst stage, and of human embryos at the 2- or 4-cell stage, using reverse transcription polymerase chain reaction (PCR) and nested PCR techniques. Moreover, we investigated the expression of Fas mRNA in human fragmented embryos. In rat embryos, Fas mRNA was expressed at the 2-cell stage only, whereas Fas L mRNA was expressed in oocytes, and at the pronuclear (1-cell) and 2-cell stages. In human embryos, Fas mRNA was expressed at the 4-cell stage only, whereas Fas L mRNA was expressed at both 2- and 4-cell stages. Human fragmented embryos expressed both Fas and Fas L mRNA. Because simultaneous expression of Fas and Fas L mRNA occurred in 2-cell rat embryos and in 4-cell human embryos, the Fas-Fas L system might be involved in the apoptotic pathway in the early embryos of these species.

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.

Embryo freezing after intracytoplasmic sperm injection

This study reports on the safety and efficiency of the cryopreservation of human embryos obtained after intracytoplasmic sperm injection. For this, we evaluated the morphological survival, the capacity of the surviving embryo to develop further in vitro and in vivo. After freezing-thawing embryos obtained after ICSI, 40% of the embryos do not survive the cryopreservation procedure. After selective transfer of further cleaving frozen-thawed embryos, pregnancy loss was 31% (subclinical pregnancy rate of 13% and miscarriage rate of 18%). As a result the livebirth rate per transferred embryos and per thawed embryo was 7 and 3% respectively. Obstetric outcome as well as further follow-up of the children born indicate that cryopreservation of ICSI embryos is a safe procedure, long term follow-up of the children born however is still warranted.