Should artificial shrinkage be performed prior to blastocyst vitrification? A systematic review of the literature and meta-analysis

Artificial shrinkage before fresh blastocyst transfer and IVF outcomes: a pilot randomized controlled study

RESEARCH QUESTION

Does artificial shrinkage before fresh blastocyst transfer improve clinical pregnancy rates in IVF?

DESIGN

In this monocentric prospective, randomized, double-blind, controlled pilot study, 150 couples undergoing fresh single-blastocyst transfer were randomized between 20 May 2018 and 22 February 2022. In the artificial shrinkage group (AS group), a single laser pulse was directed to the cellular junction of the trophectoderm on the opposite side of the inner cell mass in each blastocyst. IVF outcomes were clinical pregnancy, multiple pregnancy and live birth rates. Cell-free DNA (cfDNA) concentration was also measured by quantitative real-time PCR in the blastocyst culture medium.

RESULTS

In total, 142 couples underwent fresh single-blastocyst transfer: control group, no artificial shrinkage, n = 47; and AS group, artificial shrinkage, n = 95; An intention-to-treat (ITT) analysis was employed. After a reassessment and the exclusion of patients with major protocol deviations, 139 couples underwent fresh single-blastocyst transfer under optimal conditions: control group, n = 47; and AS group, n = 92; a per-protocol analysis was used here. The clinical and laboratory characteristics were not significantly different between the groups. The clinical pregnancy rate was similar in the control and AS groups (ITT: 48.9% versus 49.5%, P = 0.97; per protocol: 48.94% versus 51.1%, P = 0.89). The multiple pregnancy rate and the live birth rate were also similar between the groups. No significant differences in gestational age, birthweight or proportion of male/female newborns were observed. The concentration of cfDNA in the blastocyst culture medium was not associated with IVF outcome.

CONCLUSIONS

Large-scale randomized controlled trials are required to confirm these preliminary results.

The effect of laser-assisted hatching on vitrified/warmed blastocysts: the ALADDIN randomized controlled trial

OBJECTIVE

To evaluate whether laser-mediated assisted hatching (AH) performed on vitrified/warmed blastocysts before embryo transfer can improve live birth rate.

DESIGN

The "pArtiaL zonA pelluciDa removal by assisteD hatchINg of blastocysts (ALADDIN)" is a 2-center comparative study with a parallel randomized controlled design.

SETTING

University hospital.

PATIENTS

Participants were recruited between September 2018 and November 2021. They were aged 18-39 years, underwent nondonor in vitro fertilization cycles, and were scheduled for elective single embryo transfer with vitrified/warmed blastocysts. Those with uterine abnormalities, body mass index of >35 kg/m2, severe male factor infertility, or performing preimplantation genetic testing were excluded.

INTERVENTION

Assisted hatching was performed using a 1,480 nm diode laser, removing approximately one-third of the zona pellucida with continuous 0.2 ms pulses applied from the 1-5 o'clock positions.

MAIN OUTCOME MEASURES

The primary outcome was the live birth rate. Secondary end points included clinical pregnancy, miscarriage, multiple pregnancies, preterm births, obstetric and neonatal complications, and congenital anomalies.

RESULTS

Overall, 698 participants met the inclusion criteria and were randomized: 352 patients were assigned to the AH arm and 346 to the control arm. Of the participants, 105 (29.8%) and 101 (29.2%), respectively, achieved a live birth after treatment. The relative risk of live birth in patients with vitrified/warmed blastocysts treated with AH was 1.02 (95% confidence interval, 0.86-1.19). Exploratory subgroup analyses for women's age, recruiting centers, indications for in vitro fertilization, method of insemination, blastocyst quality, and days of blastocyst development failed to highlight any clinical situation that could benefit from AH in thawed blastocysts.

CONCLUSION

In patients undergoing frozen embryo transfer with vitrified/warmed blastocysts, laser AH does not improve the live birth rate. Further studies are required to rule out milder but potentially interesting benefits in specific subgroups of patients.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT03623659.

A compact, high-throughput semi-automated embryo vitrification system based on hydrogel

RESEARCH QUESTION

What is the efficiency and efficacy of the novel Biorocks semi-automated vitrification system, which is based on a hydrogel?

DESIGN

This comparative experimental laboratory study used mouse model and human day 6 blastocysts. Mouse oocytes and embryos were quality assessed post-vitrification.

RESULTS

The Biorocks system successfully automated the solution exchanges during the vitrification process, achieving a significantly improved throughput of up to 36 embryos/oocytes per hour. Using hydrogel for cryoprotective agent delivery, 12 vessels could be processed simultaneously, fitting comfortably within an assisted reproductive technology (ART) workstation. In tests involving the cryopreservation of oocytes and embryos, the system yielded outcomes equivalent to the manual Cryotop method. For example, the survival rate for mouse oocytes was 98% with the Biorocks vitrification system (n = 46) and 95% for the manual Cryotop method (n = 39), of which 46% and 41%, respectively, progressed to blastocysts on day 5 after IVF. CC-grade day 6 human blastocysts processed with the Biorocks system (n = 39) were associated with a 92% 2 h re-expansion rate, equivalent to the 90% with Cryotop (n = 30). The cooling/warming rates achieved by the Biorocks system were 31,900°C/minute and 24,700°C/minute, respectively. Oocyte quality was comparable or better post-vitrification for Biorocks than Cryotop.

CONCLUSIONS

The Biorocks semi-automated vitrification system offers enhanced throughput without compromising the survival and developmental potential of oocytes and embryos. This innovative system may help to increase the efficiency and standardization of vitrification in ART clinics. Further investigations are needed to confirm its efficacy in a broader clinical context.

The effect of an extended culture period on birth weight among singletons born after single or double vitrified embryo transfer

Aim

To evaluate the effect of an extended culture period on birth weight among singletons born after vitrified-warmed embryo transfer.

Methods

A retrospective cohort study was performed among 12400 women who gave birth to 1015, 1027, 687, and 9671 singletons after single blastocyst transfer, single cleavage-stage embryo transfer, double blastocyst transfer, and double cleavage-stage embryo transfer, respectively.

Results

The unadjusted birth weight of singletons born after vitrified blastocyst transfer were heavier than those born after cleavage-stage transfer (β=30.28, SE=13.17, P=0.022), as were the adjusted birth weights (β=0.09, SE=0.03, P=0.007). In addition, there was a 37% increased odd of having an infant with high birth weight after vitrified blastocyst transfer compared with vitrified cleavage stage transfer (OR=1.37, 95% CI:1.07-1.77).

Conclusion

The unadjusted and adjusted birth weight and odds of having an infant with high birth weight significantly increased after blastocyst transfer compared with cleavage-stage embryo transfer in vitrified-warmed cycles.

The optimal frozen embryo transfer strategy for the recurrent implantation failure patient without blastocyst freezing: thawing day 3 embryos and culturing to day 5 blastocysts

This study aimed to investigate the optimal frozen embryo transfer (FET) strategy for recurrent implantation failure (RIF) patients with three consecutive failed cleaved embryo implantations and no blastocyst preservation. This retrospective analysis was divided into three groups based on the FET strategy: thawed day 3 embryo transfer (D3 FET group); and extended culture of frozen-thawed day 3 embryos to day 5 blastocysts transfer (D3-D5 FET group); thawed blastocyst transfer (D5 FET group). Transplant cycle data were compared between the three groups. In total, 43.8% of vitrified-thawed cleavage embryos developed into blastocysts. Analysis of the three transplantation strategies showed that, compared with the D3 FET group, D3-D5 had a significantly better hCG-positivity rate and live-birth rate (P < 0.05). Pregnancy outcomes in the D3-D5 FET group and D5 FET group were similar regarding hCG-positivity rate, implantation rate, clinical pregnancy rate, and live-birth rate. Our findings propose two potentially valuable transfer strategies for patients experiencing repeated implantation failures. The D3-D5 FET approach presents a greater potential for selecting promising embryos in cases without blastocyst preservation; however, this strategy does entail the risk of cycle cancellation. Conversely, in instances where blastocyst preservation is an option, prioritizing consideration of the D5 FET strategy is recommended.

Comparative Assessment of Survival and Clinical Outcome Between Two Commercial Vitrification Kits with Different Warming Protocols After Blastocyst Culture: Potential Perspectives Toward Simplified Warming Procedures

This study investigates whether there is an effect on laboratory results and clinical outcome using commercial kits with similar vitrification but different warming procedures for blastocysts vitrified on day 5 or day 6. A single-center retrospective cohort study was performed between 2011 and 2020. A change from a stage-specific kit (Kit 1) to a universal kit (Kit 2) was undertaken in 2017. A total of 1845 untested blastocysts were warmed for single vitrified-warmed blastocyst transfers (SVBT). Eight hundred and twenty-five blastocysts were vitrified with Kit 1 and 1020 with Kit 2. Blastocyst survival was not different (96.1% versus 97.3%). Seven hundred seventy-seven SVBT were performed from Kit 1 and 981 from Kit 2. Overall clinical pregnancy and live birth rates were not different (35.4% versus 34.1% and 30.9% versus 30.5% for Kit 1 and 2, respectively). Subgroup analysis for live birth rates in relation to the day of blastocyst vitrification showed no differences (36.1% and 36.1% for day 5 and 25.4% and 23.5% for day 6 blastocysts, respectively). For both kits, the mean gestational age was not different (38.8 ± 2.5 weeks versus 38.8 ± 2.0 weeks) with a singleton birth weight of 3413 ± 571 g and 3410 ± 528 g for Kit 1 and Kit 2, respectively. Differences in warming procedures do not affect laboratory performance or clinical outcome after blastocyst vitrification. The plasticity of a human blastocyst may allow for further investigation on simplification of blastocyst warming procedures.

Oocyte and embryo cryopreservation in assisted reproductive technology: past achievements and current challenges

Cryopreservation has revolutionized the treatment of infertility and fertility preservation. This review summarizes the milestones that paved the way to the current routinary clinical implementation of this game-changing practice in assisted reproductive technology. Still, evidence to support "the best practice" in cryopreservation is controversial and several protocol adaptations exist that were described and compared here, such as cumulus-intact vs. cumulus-free oocyte cryopreservation, artificial collapse, assisted hatching, closed vs. open carriers, and others. A last matter of concern is whether cryostorage duration may impact oocyte/embryo competence, but the current body of evidence in this regard is reassuring. From social and clinical perspectives, oocyte and embryo cryopreservation has evolved from an afterthought when assisted reproduction was intended for immediate pregnancy with supernumerary embryos of secondary interest to its current purpose, which primarily is to preserve fertility long-term and more comprehensively allow for family planning. However, the initial consenting process, which still is geared to short-term fertility care, may no longer be relevant when the individuals that initially preserved the tissues have completed their reproductive journey. A more encompassing counseling model is required to address changing patient values over time.

Vitrifying multiple embryos in different arrangements does not alter the cooling rate

Vitrification is the most common method of cryopreservation of gametes in fertility clinics due to its improved survival rates compared to slow freezing techniques. For the Open Cryotop® vitrification device, the number of oocytes, or embryos, mounted onto a single device can vary. In this work, a mathematical model is developed for the cooling of oocytes and embryos (samples). The model is solved computationally, to investigate whether varying the number of samples mounted onto the Open Cryotop® affects the cooling rates, and consequently the survival rates, of vitrified samples. Several realistic spatial arrangements of samples are examined, determining their temperature over time. In this way we quantify the effect of spatial arrangement on the cooling rate. Our results indicate that neither the spatial arrangement nor the number of mounted samples has a large effect on cooling rates, so long as the volume of the cryoprotectant remains minimal. The time taken for cooling is found to be on the order of half a second, or less, regardless of the spatial arrangement or number of mounted samples. Hence, rapid cooling can be achieved for any number or arrangement of samples, as long as device manufacturer guidelines are adhered to.

Thawing day 3 embryos and culturing to day 5 may be a better method for frozen embryo transfer

PURPOSE

Does thawing cleavage embryos and culturing them for transfer as blastocysts improve pregnancy and perinatal outcomes compared to transferring thawed blastocysts?

METHODS

Retrospective, observational cohort study performed at two assisted reproductive technology centers, 2014 to 2020. A total of 450 patients with 463 thawed embryo transfer cycles were divided into 2 groups according to the embryonic developmental stage at cryopreservation and transfer: 231 thawed blastocysts (day 5 group) and 232 thawed cleavage embryos that were cultured for 2 days and transferred as blastocysts (day 3-5 group). The two groups were compared for demographics, routine parameters of IVF treatment, pregnancy rates, and perinatal outcomes.

RESULTS

Multivariable logistic regression analysis for ongoing pregnancy and delivery demonstrated that the day 3-5 group had a greater likelihood of achieving ongoing pregnancy and delivery compared to the day 5 group (OR 1.58, 95%CI 1.062-2.361, p = 0.024). Perinatal outcomes were comparable between the three groups.

CONCLUSION

Our results support culturing post-thaw cleavage embryos for 2 days and transferring them as blastocysts to increase chances of ongoing pregnancy and delivery.

Comparative study between two techniques for artificial shrinkage of blastocysts prior to vitrification: LASER pulse versus micro-needle technique in increasing chemical, clinical pregnancy and live birth rates after ICSI, a randomized controlled trial

PURPOSE

This work investigates ICSI outcome between LASER Artificial Shrinkage (LAS) and Micro-Needle Artificial Shrinkage (MNAS) before vitrification.

PATIENTS AND METHODS

Four hundred and nine women were included in the study; which were randomly divided into two groups according to the technique used for artificial shrinkage step of the blastocyst before vitrification: in the first group, Laser beam was used while in the second group the micro-needle was used. Ovarian stimulation was done before the ICSI procedure either by long, short or antagonist protocol.

RESULTS

The statistical analysis of our study revealed that there was no statistically significant difference between the two groups regarding age, number of cases, AMH, Basal FSH, BMI, male factor, usage ovarian stimulation protocol, high quality blastocysts, the mean number of transferred embryos. While, there was a statistically significant difference between two groups after thawing with p-value < .001 in favor of the LAS method regarding the morphology of originally high quality blastocysts, blastocysts healthiness (not degenerated), pregnancy rate, the implantation rates.

CONCLUSION

LASER artificial shrinkage of human blastocysts is a promising technology that could be implemented on a wider basis to improve ART practice, as our study revealed that the usage of LASER pulse for artificial shrinkage of blastocysts before vitrification has better implantation rate as well as better chemical and clinical pregnancy rate in comparison to the usage of micro-needle artificial shrinkage of blastocysts before vitrification. There is a statistically significant difference regarding live birth rate being more in the LASER group as compared to needle group, also the number of twins ether identical or non-identical are larger in laser group than in needle group but with no statistically significant difference. Clinical trials.gov ID: NCT04125017.

Metabolomic differences in blastocoel and uterine fluids collected in vivo by ultrasound biomicroscopy on rabbit embryos†

The success of embryo development and implantation depends in part on the environment in which the embryo evolves. However, the composition of the uterine fluid surrounding the embryo in the peri-implantation period remains poorly studied. In this work, we aimed to develop a new strategy to visualize, collect, and analyze both blastocoelic liquid and juxta-embryonic uterine fluid from in vivo peri-implantation rabbit embryos. Using high-resolution ultrasound biomicroscopy, embryos were observed as fluid-filled anechoic vesicles, some of which were surrounded by a thin layer of uterine fluid. Ultrasound-guided puncture and aspiration of both the blastocoelic fluid contained in the embryo and the uterine fluid in the vicinity of the embryo were performed. Using nuclear magnetic resonance spectroscopy, altogether 24 metabolites were identified and quantified, of which 21 were detected in both fluids with a higher concentration in the uterus compared to the blastocoel. In contrast, pyruvate was detected at a higher concentration in blastocoelic compared to uterine fluid. Two acidic amino acids, glutamate and aspartate, were not detected in uterine fluid in contrast to blastocoelic fluid, suggesting a local regulation of uterine fluid composition. To our knowledge, this is the first report of simultaneous analysis of blastocoelic and uterine fluids collected in vivo at the time of implantation in mammals, shedding new insight for understanding the relationship between the embryo and its local environment at this critical period of development.

[Pre-implantation genetic testing: Comparison between cleavage stage and blastocyst biopsy]

OBJECTIVES

Preimplantation genetic testing (PGT) refers to the set of techniques for testing whether embryos obtained through in vitro fertilization have genetic defect. There is a lack of global standardization regarding practices between countries or even from one center to another. In ours, biopsies are preferably performed on day 3 embryos, but also at the blastocyst stage on day 5. The blastocyst biopsy often requires systematic freezing of the embryos before obtaining the genetic results, whereas day 3 biopsy allows fresh embryo transfer of the healthy or balanced embryo after getting the genetic results. We wanted to compare the chances of success for couples performing PGT in our center according to the day of the biopsy.

METHODS

For this, we carried out a retrospective monocentric study including all PGT cycles performed between 2016 and 2019 divided into two groups: day 3 or day 5 biopsy.

RESULTS

There was no significant difference in terms of live birth rate (P=0.7375) after fresh embryo transfers, as well for pregnancy rates, clinical pregnancy rates, implantation rates and miscarriage rates. On the other hand, we observed higher live birth rates after frozen-thawed embryo transfer when the biopsy was performed on day 5 rather on day 3 (P=0.0001). We also wanted to assess what was the most efficient biopsy strategy in our laboratory. Our rates of useful embryos were similar regardless of the day of the biopsy (34% in D3 and 37.7% in D5, P=0.244). No statistical difference was found in the number of unnecessarily biopsied embryos in the two groups. But still, the percentage of embryos biopsied on D5 and immediately frozen was 42.8% (118 blastocysts), while no embryo biopsied on D3 led to this case.

CONCLUSION

Therefore, our results are in favor of generalization of the D5 biopsy as the international standard. However, the organizational, financial and logistical implications that this technic would impose make it unsystematic in our center.

Blastocoel fluid removal and melatonin supplementation in the culture medium improve the viability of vitrified bovine embryos

In this study, we investigated the effects of melatonin supplementation in the culture medium and blastocoel fluid removal (BFR) before vitrification on the quality and viability of in vitro-derived bovine embryos. After fertilization, presumptive zygotes were assigned to one of the following treatments: control, in vitro standard culture (IVC) medium; IVC + M10^-9, IVC medium supplemented 10^-9 M melatonin; or IVC + M10^-9 BFR, IVC medium supplemented with 10^-9 M melatonin plus BFR on day 7 (D7) of culture. D7 blastocysts were vitrified by the Cryotop method and, after 5 mo of storage, were warmed and incubated for an additional 72 h. The re-expansion rate was evaluated after 2 and 24 h, and the hatching rate was evaluated after 24, 48, and 72 h. At 72 h, the total number of cells (TNC); number of apoptotic cells (NAC); and expression of genes related to oxidative stress (HSPA5), cell metabolism (SLC2A3), cell repair (MSH6), placentation (KRT8 and PLAC8), and implantation (FOSL1) were assessed in the blastocysts. Less than 30% of the control blastocysts re-expanded until 2 h, whereas more than 85% of the IVC + M10^-9 and IVC + M10^-9 BFR blastocysts re-expanded (P < 0.05). The hatching rate of IVC + M10^-9 BFR blastocysts increased at all time points (P < 0.05), reaching 66.8% at 72 h of incubation. The TNC was similar among treatments (P > 0.05), regardless of vitrification/warming and re-cultivation. The NAC:TNC was smaller for melatonin-treated blastocysts (P < 0.05). BFR increased HSPA5 (P = 0.0118) expression and did not affect SLC2A3, MSH6, KRT8, and FOSL1 expression (P > 0.05). In conclusion, melatonin (10^-9 M) supplementation in the culture medium and BFR on D7 of culture increased the hatching rate 24, 48, and 72 h after warming of the vitrified embryos, indicating an improvement in cryotolerance.