[Outcome of embryo vitrification compared to slow freezing process at early cleavage stages. Report of the first French birth]

Vitrification of human blastocysts for couples undergoing assisted reproduction: an updated review

Over the past 40 years there has been a worldwide critical change in the field of assisted reproduction technology (ART), leading to the increased application of single blastocyst transfer, which is extremely important to avoid the risks of multiple pregnancy and associated complications for both mother and babies. Indeed, advancements in ART over the last few decades have been obtained thanks to several improvements, including ovarian stimulation, embryo culture conditions and, of course, progress in cryopreservation methods, especially with the application of vitrification. The ability to cryopreserve human embryos has improved significantly with vitrification compared to the initially adopted slow-freezing procedures. Since the introduction of vitrification, it has become the gold standard method to effectively cryopreserve human blastocysts. However, some new protocols are now being explored, such as the short warming procedure and even shorter exposure to the equilibration solution before vitrification, which seem to provide optimal results. Therefore, the main aim of the current narrative review, will be to illustrate the benefit of vitrification as an effective method to cryopreserve the human blastocyst and to illustrate new protocols and variations which in future may increase the performance of vitrification protocols.

Low serum progesterone on day of transfer adversely impacts ongoing pregnancy rates in hormonally prepared single blastocyst frozen embryo transfer cycles

OBJECTIVE

To evaluate if serum progesterone (P) levels on the day of transfer influence ongoing pregnancy rate (OPR) in hormonally prepared single blastocyst frozen embryo transfer (FET) cycles?

STUDY DESIGN

Single center prospective cohort study conducted between June 2021 and August 2022 analyzed 217 single good quality blastocyst FET cycles hormonally prepared with oral estradiol valerate and micronized vaginal progesterone 400 mg twice daily.

RESULTS

Mean serum P on the day of embryo transfer (ET) was 9.76 ± 5.19 ng/ml. Receiver operator curve (ROC) showed a significant predictive value of serum P levels on the day of ET for OPR, with an area under curve (AUC) (95 %CI) = 0.58 (0.49-0.66). Optimal serum P threshold for OPR was 7.7 ng/ml (Sensitivity 76.8%, Specificity 43.7%). 35.9% patients had serum P below this threshold. BMI was significantly higher (26.8 ± 3.7 vs 25.6 ± 4.3; p = 0.048) in patients with serum P < 7.7 ng/ml vs ≥ 7.7 ng/ml. OPR was significantly lower (24.4% vs 45.3%; p = 0.002) and clinical miscarriage rates significantly higher (37.9% vs 19.2%; p = 0.042) if serum P < 7.72 ng/ml vs ≥ 7.7 ng/ml.

CONCLUSION

This study found that serum P level on the day of transfer in hormonally prepared FET cycles was a significant predictor of OPR.

Women utilizing oocyte donation have a decreased live birth rate if they displayed a low progesterone level in a previous hormonal replacement mock cycle

PURPOSE

Is serum progesterone(P) level on day 2 of vaginal P administration in a hormonally substituted mock cycle predictive of live birth in oocyte donation(OD)?

METHODS

Retrospective analysis of 110 mock cycles from 2008 to 2016 of OD recipients having at least one subsequent embryo transfer (ET). Endometrial preparation consisted of sequential administration of vaginal estradiol, followed by transdermal estradiol and 600 mg/day vaginal micronized P. In mock cycles, serum P was measured 2 days after vaginal P introduction. OD was performed 1 to 3 years later, without P measurement.

RESULTS

In mock cycles, mean serum P level on day 2 was 12.8 ± 4.5 ng/mL (range: 4-28 ng/mL). A total of 32% patients had P < 10 ng/mL. At the time of first OD, age of recipients and donors, number of retrieved and attributed oocytes, and number of transferred embryos were comparable between patients with P < 10 ng/mL in their mock cycles compared with P ≥ 10 ng/mL. Pregnancy and live birth rate after first ET were significantly lower for patients with P < 10ng/mL (9% vs. 35 %; P = 0.002 and 9% vs. 32%; P = 0.008, respectively). Considering both fresh and subsequent frozen-thawed ET, cumulative live birth rate per-patient and per-transfer were significantly lower in patients with P < 10 ng/mL in their mock cycle (14% vs. 35%; P = 0.02 and 11% vs. 27%; P = 0.03).

CONCLUSION

A low P level in hormonally substituted cycles several years before ET performed with the same endometrial preparation is associated with a significantly lower chance of live birth. This suggests that altered vaginal P absorption is a permanent phenomenon. Monitoring serum P in hormonally substituted cycles appears mandatory to adjust luteal P substitution.

Do serum progesterone levels on day of embryo transfer influence pregnancy outcomes in artificial frozen-thaw cycles?

PURPOSE

The purpose of this study is to investigate whether progesterone (P4) levels on the day of frozen-thawed embryo transfer (FET) to a hormonally prepared endometrium correlate with pregnancy outcomes.

METHODS

This is a large retrospective cohort analysis comprising of N = 2010 FETs. In these cycles, P4 levels on the day of transfer were assessed in relation to pregnancy outcomes. A threshold of 10 ng/mL was used to simulate currently accepted levels for physiological corpus luteal function. Biochemical pregnancy, clinical pregnancy, and live birth rates were compared between those with P4 levels above and below this threshold. Analyses using transfer day P4 thresholds of 5 ng/mL and 20 ng/mL were then completed to see if these could create further prognostic power.

RESULTS

When comparing FET outcomes in relation to P4 levels < 10 ng/mL and ≥ 10 ng/mL, we observed no differences in biochemical pregnancy rates (39.53% vs. 40.98%, p = 0.52), clinical pregnancy rates (20.82 vs. 22.78, p = 0.30), and live birth rates (14.25 vs. 16.21 p = 0.23). In patients whose P4 met the threshold of 20 ng/mL, there was similarly no statistically significant improvement in pregnancy outcomes. While there was no difference for biochemical or clinical pregnancy rates, a statistically significant improvement in live birth rates was observed for those with a transfer day P4 level ≥ 5 ng/mL.

CONCLUSIONS

We demonstrated that P4 levels at or above 10 ng/mL on the day of FET do not confer a statistically significant improvement in pregnancy outcomes. P4 below 5 ng/mg was associated with lower live birth rates suggesting that there is a threshold below which it is difficult to salvage FET cycles.

Is it worth it to cryopreserve embryos with blastulation delay at day 5?

This is a retrospective study over a 5-year period. In total, 3139 embryos were individually cryopreserved (Cryotop®) and warmed using the Kitazato vitrification/warming kit. They were classified into three categories based on their expansion degree. Transfer, implantation and pregnancy rates were assessed for each embryo category and compared using SPSS (Statistical Package for the Social Sciences) software. In total, 1139 couples enrolled in infertility treatment programme benefitted from embryo vitrification at day 5. After warming, embryos belonging to the three categories showed similar success rates. Although there was a trend towards better outcomes when grade 3 embryos were transferred, the differences did not reach statistical significance: implantation rates (n fetal sac/n embryo transferred) grade 1: 21.9%, grade 2: 22.7% and grade 3: 30.3% (=0.19). Pregnancy rate (n clinical pregnancy/n transfer) (21.9%, 22.7%, 30.3%, respectively; P=0.11). Miscarriage rate was not statistically different in the three categories (14.5%, 20.4%, 20%, respectively, P=0.51). Our overall results show that it is worth vitrifying slow kinetics embryos as they provide a non-negligible chance to give rise to a pregnancy.

Impact of post-warming culture duration on clinical outcomes of vitrified good-quality blastocyst transfers: a prospective randomized study

OBJECTIVE

To determine whether post-warming culture duration (1 hour vs. 18 hours) influences implantation rates (IRs) of good-quality blastocysts (GQB) in a good-prognosis population.

DESIGN

Prospective interventional randomized study.

SETTING

University hospital.

PATIENT(S)

One hundred sixty-two GQB transfers.

INTERVENTION(S)

Patients' vitrified blastocysts were randomly allocated to group A, warming on the day before transfer (n = 81), or B, warming on the day of transfer (n = 81).

MAIN OUTCOME MEASURE(S)

IR, live birth rate, reexpansion degree, and quality after warming and immediately before transfer.

RESULT(S)

Quality of the warmed and transferred blastocysts was similar (respectively, 39.1% and 32.7% top quality [≥B4AA/AB/BA] in group A vs. 41.7 and 42.2% in group B). In group A, 14 of 102 blastocysts (12.2%) appeared to be unsuitable for transfer, versus only 1 of 103 (0.9%) in group B, thus leading to an additional warming. As expected, reexpansion degree just before transfer was higher in group A (0.90 vs. 0.70). Likewise, the proportion of hatched blastocysts before transfer was higher after a longer culture period (38.6% in group A vs. 12.7% in group B). IRs were similar (38.0% in group A vs. 36% in group B), as were live birth rates (35.8% in group A vs. 34.6% in group B).

CONCLUSION(S)

IRs were not different, whatever the duration of post-warming culture of GQB. Both warming strategies could be applied to good-prognosis patients to optimize the laboratory workflow without any detrimental effect.

Oocyte, embryo and blastocyst cryopreservation in ART: systematic review and meta-analysis comparing slow-freezing versus vitrification to produce evidence for the development of global guidance

BACKGROUND

Successful cryopreservation of oocytes and embryos is essential not only to maximize the safety and efficacy of ovarian stimulation cycles in an IVF treatment, but also to enable fertility preservation. Two cryopreservation methods are routinely used: slow-freezing or vitrification. Slow-freezing allows for freezing to occur at a sufficiently slow rate to permit adequate cellular dehydration while minimizing intracellular ice formation. Vitrification allows the solidification of the cell(s) and of the extracellular milieu into a glass-like state without the formation of ice.

OBJECTIVE AND RATIONALE

The objective of our study was to provide a systematic review and meta-analysis of clinical outcomes following slow-freezing/thawing versus vitrification/warming of oocytes and embryos and to inform the development of World Health Organization guidance on the most effective cryopreservation method.

SEARCH METHODS

A Medline search was performed from 1966 to 1 August 2016 using the following search terms: (Oocyte(s) [tiab] OR (Pronuclear[tiab] OR Embryo[tiab] OR Blastocyst[tiab]) AND (vitrification[tiab] OR freezing[tiab] OR freeze[tiab]) AND (pregnancy[tiab] OR birth[tiab] OR clinical[tiab]). Queries were limited to those involving humans. RCTs and cohort studies that were published in full-length were considered eligible. Each reference was reviewed for relevance and only primary evidence and relevant articles from the bibliographies of included articles were considered. References were included if they reported cryosurvival rate, clinical pregnancy rate (CPR), live-birth rate (LBR) or delivery rate for slow-frozen or vitrified human oocytes or embryos. A meta-analysis was performed using a random effects model to calculate relative risk ratios (RR) and 95% CI.

OUTCOMES

One RCT study comparing slow-freezing versus vitrification of oocytes was included. Vitrification was associated with increased ongoing CPR per cycle (RR = 2.81, 95% CI: 1.05-7.51; P = 0.039; 48 and 30 cycles, respectively, per transfer (RR = 1.81, 95% CI 0.71-4.67; P = 0.214; 47 and 19 transfers) and per warmed/thawed oocyte (RR = 1.14, 95% CI: 1.02-1.28; P = 0.018; 260 and 238 oocytes). One RCT comparing vitrification versus fresh oocytes was analysed. In vitrification and fresh cycles, respectively, no evidence for a difference in ongoing CPR per randomized woman (RR = 1.03, 95% CI: 0.87-1.21; P = 0.744, 300 women in each group), per cycle (RR = 1.01, 95% CI: 0.86-1.18; P = 0.934; 267 versus 259 cycles) and per oocyte utilized (RR = 1.02, 95% CI: 0.82-1.26; P = 0.873; 3286 versus 3185 oocytes) was reported. Findings were consistent with relevant cohort studies. Of the seven RCTs on embryo cryopreservation identified, three met the inclusion criteria (638 warming/thawing cycles at cleavage and blastocyst stage), none of which involved pronuclear-stage embryos. A higher CPR per cycle was noted with embryo vitrification compared with slow-freezing, though this was of borderline statistical significance (RR = 1.89, 95% CI: 1.00-3.59; P = 0.051; three RCTs; I2 = 71.9%). LBR per cycle was reported by one RCT performed with cleavage-stage embryos and was higher for vitrification (RR = 2.28; 95% CI: 1.17-4.44; P =  0.016; 216 cycles; one RCT). A secondary analysis was performed focusing on embryo cryosurvival rate. Pooled data from seven RCTs (3615 embryos) revealed a significant improvement in embryo cryosurvival following vitrification as compared with slow-freezing (RR = 1.59, 95% CI: 1.30-1.93; P < 0.001; I2 = 93%).

WIDER IMPLICATIONS

Data from available RCTs suggest that vitrification/warming is superior to slow-freezing/thawing with regard to clinical outcomes (low quality of the evidence) and cryosurvival rates (moderate quality of the evidence) for oocytes, cleavage-stage embryos and blastocysts. The results were confirmed by cohort studies. The improvements obtained with the introduction of vitrification have several important clinical implications in ART. Based on this evidence, in particular regarding cryosurvival rates, laboratories that continue to use slow-freezing should consider transitioning to the use of vitrification for cryopreservation.

Oxidative markers in cryopreservation medium from frozen-thawed embryos: a possible tool for improved embryo selection in in vitro fertilization?

PURPOSE

The present study evaluated the association between oxidative parameters in embryo cryopreservation medium and laboratory and clinical outcomes.

METHODS

This prospective laboratory study was conducted in an IVF unit in a university-affiliated hospital with 91 IVF patients undergoing a frozen-thawed embryo transfer cycle. Following thawing, 50 μL of embryo cryopreservation medium was retrieved from each cryotube and tested by the thermochemiluminescence (TCL) assay. TCL amplitudes after 50 (H1), 150 (H2), and 280 s (H3) were recorded in counts per second (CPS) and the TCL ratio determined for comparison with implantation and pregnancy rates.

RESULTS

A total of 194 embryos were transferred in 85 frozen-thaw cycles. Twenty-one pregnancies (24.7 %) occurred. Implantation and overall and clinical pregnancy rates were higher when the median TCL H1 amplitude was <32 CPS compared to ≥32 CPS (14.6 vs. 5.3 %, 37.5 vs. 17 %, 28.1 vs. 9.4 %, respectively). No pregnancies occurred when the H1 amplitude was ≥40 CPS. Logistic regression multivariate analysis found that only the median TCL H1 amplitude was associated with the occurrence of pregnancy (OR = 2.93, 95 % CI 1.065-8.08). The TCL ratio inversely correlated with the duration of embryo cryopreservation (r = -0.37).

CONCLUSIONS

The results indicate that thawed embryos may express oxidative processes in the cryopreservation medium, and higher oxidative levels are associated with lower implantation rates. These findings may aid in the improved selection of frozen-thawed embryos for IVF.

[Contribution of embryo vitrification procedure to ART efficiency]

This work aims to show, from data available in the literature and our own experience, how embryos' vitrification change and/or improve the management of infertile couples. In all, 652 cycles of frozen-thawed embryo transfers (FET) following vitrification were prospectively included and compared with 1126 FETs from slow freezing (SF) method. Primary end points were the (i) survival rate (SR) (% of embryos with>50% post-thaw intact blastomeres) and (ii) intact survival rate (ISR) (% of embryos with 100% post-thaw intact blastomeres). Secondary end point was the clinical pregnancy rate (CPR) defined as the presence of an intra uterine gestational sac with positive foetal heart beat. In all, 1097 and 2408 embryos have been thawed following vitrification and SF, respectively. We observed a highly significant increase of SR and ISR respectively when thawing concerned vitrified embryos rather than those from SF method (97.0% vs. 72.7%, P<10(-4); 91.5% vs. 49.8%, P<10(-4)). Furthermore, CPR were of 26.5% (73/652) and of 18.1% (204/1126) following FETs performed after vitrification or SF and thawing (P=0.0002), respectively. At the blastocyst stage, ISR was significantly improved following vitrification compared to SF (94.5% vs. 21.4%, P<10(-4)). In the study period, vitrification (i) reduced the mean number of fresh transferred embryos (1.5 vs. 1.6; P=0.08) and (ii) increased the rate of FETs at the blastocyst stage when compared with the control period (18.1% vs 2.5%., P<10(-4)). Embryo vitrification preserves all embryos from an ART cycle because of its excellent results regarding ISR at all stages of embryo development. This procedure allows a significant increase of pregnancy rates after thawing. In addition, there is a trend for increasing ART cycles performed using extended culture embryo and vitrification. The expected improvement of the cumulative birth rate at the blastocyst stage following vitrification remains to be demonstrated in a prospective randomized study.