Laser technology in the ART laboratory: a narrative review

Time and power dependence of laser-induced photodamage on human sperm revealed by longitudinal rolling measurement using optical tweezers

Lasers are widely applied in assisted reproductive technologies, including sperm fixation, sperm selection and intracytoplasmic sperm injections, to reduce procedure time and improve consistency and reproducibility. However, quantitative studies on laser-induced photodamage of sperm are lacking. In this study, we demonstrated that, by using optical tweezers, the kinematic parameters of freely swimming sperm are correlated with the frequency as well as the percentage of pausing duration of longitudinal rolling of the same sperm head in the optical trap. Furthermore, by trapping individual sperm cells using 1064-nm optical tweezers, we quantitatively characterized the time-dependence of longitudinal rolling frequency and percentage of pausing duration of sperm under different laser powers. Our study revealed that, as trapping time and the laser power time increase, the longitudinal rolling frequency of the optically trapped sperm decreases with an increasing percentage of pausing duration, which characterizes the effect of laser power and duration on the photodamage of individual sperm cells. Our study provides experimental basis for the optimization of laser application in assisted reproductive technology, which may reduce the photodamage-induced biosafety risk in the future.

Unlocking the Potential of Assisted Hatching in Assisted Reproductive Technology: A Narrative Review

The present study is set in the broad field of assisted reproductive technologies (ARTs) and examines various procedures under assisted hatching (AH). It also reviews their effects on implantation success rates. The primary emphasis is on explaining who has benefited and how many have benefited from these interventions. The most important factor determining the success rate of ART is implantation. To increase these rates, we use AH in our clinics to enhance each embryo's chances at life and substantially improve overall results. This comprehensive review includes various approaches, such as chemical-based measures (such as applying Tyrode's solution) and mechanical techniques (such as zona drilling and partial zona dissection). The individual techniques are carefully scrutinized, considering their mechanical detailing, methods of applying therapeutic effects, and the appropriateness of matching present social circumstances. The review begins by analyzing the basic nature of AH as a medium for embryo implantation and then focuses on how this detailed view reveals the advantages and drawbacks of various methods. Moreover, the articles discuss improvements in AH technology and many of the most modern technological developments that can help fine-tune ART issues. A major problem with these methodologies is that they involve serious risks and legal complications. However, a broad assessment of these topics allows us to understand their impact on fertility treatments. This review is written as a guidebook for physicians and researchers working in reproductive medicine. It compiles all current knowledge, providing literature to build on successes that will make breakthroughs possible in ART. Indeed, this is a valuable reference for guiding us in navigating complex AH procedures. It advances ARTs step by step toward perfection.

Applications of laser technology in the manipulation of human spermatozoa

The application of laser technology in the field of assisted reproductive technology (ART) has experienced rapid growth over the past decades owing to revolutionary techniques such as intracytoplasmic sperm injection (ICSI), preimplantation genetic testing (PGT), and in vitro manipulation of gametes and embryos. For male gametes, in vitro manipulation techniques include spermatozoa selection, sorting, immobilization, and quality assessment. A number of studies have been conducted to investigate the application of different laser technologies in the manipulation of human spermatozoa. However, there is a lack of a unified understanding of laser application in the in vitro manipulation of sperm and safety considerations in ART and, subsequently, the inability to make clear and accurate decisions on the clinical value of these laser technologies. This review summarizes the advancements and improvements of laser technologies in the manipulation of human spermatozoa, such as photobiomodulation therapy, laser trap systems for sperm analysis and sorting, laser-assisted selection of immotile sperm and laser-assisted immobilization of sperm prior to ICSI. The safety of those technologies used in ART is also discussed. This review will provide helpful and comprehensive insight into the applications of laser technology in the manipulation of human spermatozoa.

Laser-assisted hatching improves pregnancy outcomes in frozen-thawed embryo transfer cycles of cleavage-stage embryos: a large retrospective cohort study with propensity score matching

INTRODUCTION

Laser-assisted hatching (LAH) is a commonly used adjunct technique; however, its effectiveness has not been fully established.

OBJECTIVE

We evaluated the effects of LAH on pregnancy outcomes in frozen-thawed embryo transfer (FET) cycles of cleavage-stage embryos.

MATERIALS AND METHODS

This retrospective study involved 5779 FET cycles performed at the Reproductive and Genetic Center in the Affiliated Hospital of Shandong University of Traditional Chinese Medicine between January 2016 and December 2020. After propensity score matching, 3535 FET cycles were included, out of which 1238 were subjected to LAH while the remaining 2297 cycles were non-LAH (NLAH). The primary outcomes were clinical pregnancy rate (CPR) and live birth rate (LBR) while secondary outcomes included implantation rate (IR), biochemical pregnancy rate (BPR), ectopic pregnancy rate (EPR), pregnancy loss rate (PLR), multiple pregnancy rate (MPL), and monozygotic twinning rate (MTR). Logistic regression analysis was conducted to adjust for possible confounders. Subgroup analysis was also performed based on the endometrial preparation regimen.

RESULTS

The LAH group exhibited a higher LBR, compared to the NLAH group (34.9% vs. 31.4%, OR = 1.185, 95% CI = 1.023, 1.374, P = 0.024). Additionally, the LAH group showed a decreasing trend in PLR and EPR; however, differences were insignificant (P = 0.078, P = 0.063 respectively). Differences in IR (24.6% vs. 24.3%), BPR (41.8% vs. 40.4%), CPR (40.7% vs. 38.3%), MPR (14.1% vs. 17.3%), and MTR (1.4% vs. 1.1%) were insignificant. Subgroup analysis revealed that LAH may be more conducive for pregnancy outcomes in hormone replacement cycles.

CONCLUSIONS

In summary, LAH has an increased chance of achieving live births. However, further prospective studies should be performed to confirm our findings.

Thinning or Opening: A Randomized Sibling-Embryo Pilot Trial on the Efficacy of Two Laser-Assisted Hatching Modes During the Extended Culture of Highly Fragmented Cleavage Embryos

A randomized sibling-embryo pilot trial investigated whether two ways of laser-assisted hatching result in different blastulation and clinical outcomes after extended in vitro culture process of highly fragmented day-3 cleavage embryos. From 92 couples, a total of 315 highly fragmented day-3 embryos (the fragmentation >25%) were recruited and randomized into laser-assisted zona thinning (LAT, n=157) and opening (LAO, n=158) groups, and then underwent a blastocyst culture in vitro. The main endpoint measurements including blastocyst formation and grading as well as the clinical pregnancy after blastocyst transfer were obtained during the treatment procedure of in vitro fertilization and embryo transfer, and then analyzed with generalized estimating equation (GEE) and/or time-to blastocyst analysis models. A total of 166 day-3 embryos developed into blastocyst stage (52.70%), of which 97 were viable blastocysts (30.79%), and 42 top-quality ones (13.33%). LAT did not have any inferior or superior to LAO in the endpoints of either total, viable, top-quality or hatched blastocyst formation, with the ORs (95%CI) from GEE model as 0.89 (0.55-1.45), 0.71 (0.42-1.21), 1.12 (0.56-2.25) and 0.68 (0.42-1.12) respectively for LAT treatment. And the time-to-blastocyst analysis showed a similar result. Additionally, no difference in clinical outcomes after blastocyst transfer was found between the two groups. The author concluded that when applying the LAHs during the extended culture of highly fragmented embryos, both LAT and LAO can generate a promising clinical outcome, and the LAT operation be equivalent to the LAO. Future well-designed, multiple-center, larger-sample investigations are required to ascertain above conclusion.

Non-Assisted Hatching Trophectoderm Biopsy Does Not Increase The Risks of Most Adverse Maternal and Neonatal Outcome and May Be More Practical for Busy Clinics: Evidence From China

OBJECTIVE

This study was conducted in order to investigate whether non-assisted hatching trophectoderm (TE) biopsy increases the risks of adverse perinatal outcomes in livebirths following elective single cryopreserved-thawed blastocyst transfer.

PATIENTS AND METHODS

A total of 5,412 cycles from 4,908 women who achieved singleton livebirths between 2013 and 2019 were included in this retrospective cohort study. All embryos in this study were fertilized by intracytoplasmic sperm injection (ICSI) and cryopreserved through vitrification. The main intervention is to open the zona pellucida (ZP) of day 5/6 blastocyst immediately for biopsy without pre-assisted hatching. The main outcome measures are the common maternal and neonatal outcomes, including hypertensive disorders of pregnancy (HDPs), gestational diabetes mellitus (GDM), abnormal placentation, abnormalities in umbilical cord and amniotic fluid, preterm birth, cesarean section, low birth weight, postpartum hemorrhage, and prolonged hospital stay (both mothers and infants). The generalized estimation equation (GEE) was used to control the effects of repeated measurements. The non-conditional logistic regression model was used to examine the associations between embryo biopsy status and each adverse perinatal event. Given that the selection bias and changes in learning curve might affect the results, we selected 1,086 similar (matching tolerance = 0.01) cycles from the ICSI group via propensity score matching (PSM) for second comparisons and adjustment (conditional logistic regression).

RESULTS

After adjusting for confounders, we confirmed that the non-assisted hatching protocol did not increase the risks of most adverse maternal and neonatal outcomes. Despite this, there were increased risks of GDM (aOR: 1.522, 95% CI: 1.141-2.031) and umbilical cord abnormalities (aOR: 11.539, 95% CI: 1.199-111.067) in the biopsy group. In the second comparisons after PSM, GDM incidence in the biopsy group was still higher (7.26% vs. 5.16%, P = 0.042), yet all measurement outcomes were equally likely to occur in both groups after the second adjustment.

CONCLUSIONS

The non-assisted hatching TE biopsy does not increase the risks of most adverse perinatal outcomes. However, there is a higher GDM incidence in the biopsy group, and this association warrants further study. Considering its safety and simplicity, the non-assisted hatching protocol has the potential to become the preferred option for TE biopsy, especially in busy clinics and IVF laboratories.

An investigation of the effects of laser-assisted zona pellucida drilling on the preimplantation mouse embryo and the competency of embryo implantation

OBJECTIVE

To investigate the impact of laser-assisted zona pellucida (ZP) drilling on the mouse embryo, with particular emphasis on molecular mechanisms, and the efficiency of embryo attachment capability using an in vitro model of implantation.

DESIGN

Experimental study.

SETTING

Academic research laboratory.

ANIMAL(S)

C57BL/6JOlaHsd mouse embryos and B6C3F1 × B6D2F1 mouse embryos.

INTERVENTION(S)

Eight-cell stage mouse embryos were randomly assigned to a laser-assisted ZP drilling group (n = 343), ZP partial drilling group (n = 312), ZP quarter thinning group (n = 289), and control group (n = 353). Embryos were cultured in vitro from E2.5 to E4.5 for 48 hours. To investigate the capacity to implant, E4.5 embryos (laser-assisted drilling group [n = 46], ZP partial drilling group [n = 28], ZP quarter thinning group [n = 26], and control group [n = 36]) were then transferred onto an attachment model on the basis of Ishikawa cells and cultured for another 72 hours.

MAIN OUTCOME MEASURE(S)

Blastocyst formation, hatching status, and hatching morphology at E4.5. Blastocyst cell components, the extent of apoptosis in embryonic cells (DNA fragmentation, caspase-3 activation, and expression of apoptosis-related genes), the expression of heat shock protein 70, and differentially expressed genes (DEGs) generated by RNA sequencing. Fully hatched embryo rate and stable attachment rate in the in vitro attachment model.

RESULT(S)

There were no significant differences between the laser-assisted ZP manipulation groups and control group with respect to the formation of blastocysts, cell number, embryonic cell apoptosis, and cellular stress. All 3 of the laser-assisted ZP manipulations significantly increased the hatching rate at E4.5 compared with the control group, especially the ZP drilling group. However, only the ZP drilling group was associated with a significantly higher proportion of "8"-shaped hatching blastocysts. Furthermore, RNA sequencing identified 48 DEGs between blastocysts from the laser-assisted drilling group and control group; the metabolic pathways were significantly enriched in these DEGs. In addition, there were no significant differences between the laser-assisted ZP manipulation groups and control group with respect to the rate of stable attachment at E7.5, although a significantly higher entrapment rate was observed in the ZP drilling group.

CONCLUSION(S)

Laser-assisted ZP manipulations did not induce cellular apoptosis or stress in mouse blastocysts. Nevertheless, for the first time, we found that laser-assisted ZP drilling could alter the embryonic transcriptome and may affect metabolic activity. Furthermore, although laser-assisted ZP manipulations can enhance the initiation of hatching, it is evident that ZP drilling comes with a potential risk of embryo entrapment.

From Zygote to Blastocyst: Application of Ultrashort Lasers in the Field of Assisted Reproduction and Developmental Biology

Although the use of lasers in medical diagnosis and therapies, as well as in fundamental biomedical research is now almost routine, advanced laser sources and new laser-based methods continue to emerge. Due to the unique ability of ultrashort laser pulses to deposit energy into a microscopic volume in the bulk of a transparent material without disrupting the surrounding tissues, the ultrashort laser-based microsurgery of cells and subcellular components within structurally complex and fragile specimens such as embryos is becoming an important tool in developmental biology and reproductive medicine. In this review, we discuss the mechanisms of ultrashort laser pulse interaction with the matter, advantages of their application for oocyte and preimplantation embryo microsurgery (e.g., for oocyte/blastomere enucleation and embryonic cell fusion), as well as for nonlinear optical microscopy for studying the dynamics of embryonic development and embryo quality assessment. Moreover, we focus on ultrashort laser-based approaches and techniques that are increasingly being applied in the fundamental research and have the potential for successful translation into the IVF (in vitro fertilization) clinics, such as laser-mediated individual embryo labelling and controlled laser-assisted hatching.

Evaluating the use of piezo manipulator, laser or their combination for blastocoel cavity puncture to improve cryopreservation outcomes of large equine embryos

The main difficulty of large equine embryo cryopreservation is the replacement of blastocoel fluid with cryoprotectant solution. The objective of this study was to improve the cryopreservation of large equine embryos with PMAP and/or LAP. Embryos were collected via the non-surgical transcervical procedure and divided into three groups based on their size (A ≤ 300 µm, 300 µm<B < 700 µm and C ≥ 700 µm). Six embryos 233-1360 µm in diameter were punctured via piezo manipulator and/or laser pulse before cryopreservation. All embryos were cryopreserved on a Cryotop®. Frozen-thawed embryos were cultured for 3h and transferred to the recipient mares. After one week, pregnancy was diagnosed by ultrasonography. Two of six embryos resulted in a positive pregnancy, the result of pregnancy in group A and B was positive, but in group C was negative, and further investigation is necessary for ≥700 µm embryos. The results showed laser-assisted puncture could be helpful to extract blastocoel fluid and replace it with cryoprotectant. This is the first positive pregnancy report in laser puncture-assisted frozen-thawed equine embryo (>300 µm). However, more research is required to find the best method for embryos ≥700 µm.

Laser-assisted hatching on clinical and neonatal outcomes in patients undergoing single vitrified Blastocyst transfer: A propensity score-matched study

PURPOSE

This study determined the effect of laser-assisted hatching on the clinical and neonatal outcomes of single vitrified blastocyst transfer.

METHODS

From June 2014 to March 2018, 289 matched pairs after propensity score matching were analyzed. During the blastocyst warming procedure, a small section of the zona pellucida area in the empty perivitelline space was sliced off using multiple laser beams. The clinical and neonatal outcomes of the laser-treated group and non-treatment control were analyzed.

RESULTS

In the laser-assisted hatching group, significantly higher rates of clinical pregnancy (40.8% vs 29.4%, P < .01) and live delivery (34.3% vs 22.5%, P < .01) were observed compared to the control group. Other variables such as the average gestational weeks, the sex of the baby, birthweight, or congenital malformations were found to have no significant differences in neonatal outcomes. Moreover, all babies were singleton live births.

CONCLUSIONS

Single vitrified blastocyst transfer treated with laser-assisted hatching increases the live birth rate and has no adverse effects on neonatal outcomes.

Repeated cryopreservation process impairs embryo implantation potential but does not affect neonatal outcomes

RESEARCH QUESTION

Does repeated cryopreservation process affect embryo implantation potential and neonatal outcomes of human embryos?

DESIGN

This retrospective cohort study was conducted in the Reproductive Medicine Centre, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology. All assisted reproductive technology (ART) cycles were carried out between January 2014 and December 2018. Preferentially matched participants were divided into three groups according to the times of embryo cryopreservation: the fresh group (n = 249), the cryopreservation group (n = 244) and the re-cryopreservation group (n = 216). Embryo implantation rate, live birth rate, miscarriage rate and neonatal complication rate were compared among these three groups.

RESULTS

The embryo implantation rate, clinical pregnancy rate and live birth rate in the re-cryopreservation group were significantly lower, and the miscarriage rate also slightly increased. Logistic regression analysis indicated that embryos with repeated cryopreservation and lower trophectoderm scores were at higher risk of embryo implantation failure in single embryo transfer cycles (OR 1.79 and 1.56, respectively). No significant differences were observed in gender, gestational age, birthweight, neonatal abnormality and neonatal complications among the groups.

CONCLUSIONS

Our findings demonstrate the adverse effect of repeated cryopreservation on embryo implantation potential. The study offers embryologists and reproductive clinicians a warning of detrimental role of repeated cryopreservation. If unnecessary, it is strongly recommended to avoid repeated practice of vitrification and warming on embryos.

Controlled hatching at the prescribed site using femtosecond laser for zona pellucida drilling at the early blastocyst stage

PURPOSE

To study whether the application of femtosecond laser pulses for zona pellucida (ZP) drilling of blastocysts at the embryonic or abembryonic poles can promote hatching to start immediately through the hole formed and ensure high hatching rates and embryo viability.

METHODS

Mouse blastocyst (E3.5) ZP were microdissected with femtosecond laser pulses (514-nm wavelength, 280-fs pulse duration, 2.5-kHz repetition rate) close to the trophoblast or inner cell mass (ICM). The sizes of the holes formed were in the range of 4.5-8.5 μm. Additional longitudinal incisions (5-7-μm long) on either side of the hole were created to determine whether hatching had started at the correct position. Embryos post-laser-assisted ZP drilling and intact embryos were cultured under standard conditions for 2 days; embryo quality was assessed twice daily. The hatching rates and in vitro and in vivo implantation rates (only for embryos with ZP dissected close to the ICM) were estimated.

RESULTS

Femtosecond laser-assisted ZP drilling at the early blastocyst stage facilitated embryo hatching to start at the artificial opening with probability approaching 100%. Despite the artificial opening's small size, no embryo trapping during hatching was observed. Both experimental groups had higher hatching rates than the control groups (93.3-94.7% vs. 83.3-85.7%, respectively). The in vitro implantation rate was comparable with that of the control group (92.3% vs. 95.4%). No statistically significant differences were obtained in the in vivo implantation rates between the experimental and control groups.

CONCLUSIONS

Blastocyst-stage femtosecond laser microsurgery of ZP is fast and delicate and enables the hatching process to be initiated in a controlled manner through a relatively small opening, with no embryo trapping.

Evaluating the value of day 0 of an ICSI cycle on indicating laboratory outcome

A number of oocyte characteristics have been associated with fertilization, implantation and live-birth rates, albeit without reaching a consensus. This study aims to delineate possible associations between oocyte characteristics, oocyte behavior during intracytoplasmic sperm injection (ICSI), fertilization potential, and laboratory outcomes. Four-hundred and seventy-seven patients, yielding 3452 oocytes, were enrolled in this prospective observational study from 2015 to 2018. Οoplasm granularity was associated with poor embryo quality and higher probabilities of post-ICSI oocytes and embryos discarded in any developmental stage and never selected for embryo transfer or cryopreservation (p < 0.001). Both sudden or difficult ooplasm aspiration, and high or lack of resistance during ICSI were associated with either a poor Zygote-Score or fertilization failure (p < 0.001). Sudden or difficult ooplasm aspiration and high resistance during ICSI penetration were positively associated with resulting to a post-ICSI oocyte or embryo that would be selected for discard. Evaluation of oocyte characteristics and oocyte behavior during ICSI may provide early information regarding laboratory and cycle outcomes. Particularly, ooplasm granularity, and fragmentation of polar body, along with sudden or difficult ooplasm aspiration and high or lack of resistance during ICSI penetration may hinder the outcome of an ICSI cycle. The associations presented herein may contribute towards development of a grading system or a prediction model. Taking into account information on oocytes and ICSI behavior may effectively assist in enhancing IVF outcome rates.

Trophectoderm biopsy for preimplantation genetic test and technical tips: A review

BACKGROUND

Recently, the Japan Society of Obstetrics and Gynecology initiated a clinical study of preimplantation genetic test for aneuploidy. There will be a great need for a standardized embryo biopsy technique in Japan. However, the gold standard trophectoderm (TE) biopsy procedure has not been established, and this review outlines the clinical use of TE biopsy.

METHODS

Based on literature, the method and associated techniques for TE biopsy, a dissection method of TE cells from blastocysts, were investigated.

MAIN FINDINGS

Two TE biopsy methods are used, namely assisted hatching (herniating) and non-assisted hatching (direct suction); however, it is not clear which of these methods is superior. It is critical to understand whether the flicking or pulling method is beneficial.

CONCLUSION

Non-assisted hatching biopsy method may cause blastocyst collapse with a higher probability, and it may extend the biopsy time. The biopsy procedure should be performed within 3 minutes, and thus direct TE suction may have greater disadvantages. It is a fact that pulling method of TE dissection with laser pulse is simple; however, excess laser shots may induce a higher frequency of mosaicism. It is important to understand that each technique of TE biopsy has benefits and disadvantages.

Expansion and herniation: evaluation of the best pregnancy rate predictor after quarter laser assisted hatching in frozen blastocyst transfers

Objective

To assess the recovery of thawed blastocysts submitted to quarter laser assisted hatching and examine potential correlations between the procedure and pregnancy rates.

Methods

This cross-sectional study included only single-blastocyst transfers performed from July 2017 to December 2018. A total of 765 blastocysts were thawed and immediately submitted to quarter laser assisted hatching in the zona pellucida; they were subsequently incubated for three hours until transfer time, at which time they were examined for collapse or expansion; expanded blastocysts were further evaluated for herniation. The Chi-square test was used in statistical analysis.

Results

627 blastocysts expanded (81.9%) and yielded a pregnancy rate of 40% (251/627). 138 blastocysts collapsed after thawing (18.0%) and yielded a pregnancy rate of 25.4% (35/138) (p=0.001). Additional analysis of the subgroup of expanded blastocysts revealed that the 385 herniated blastocysts (61.4%) yielded a pregnancy rate of 43.9% (169/385). The remaining 242 non-herniated blastocysts (38.6%) yielded a pregnancy rate of 33.9% (82/242) (p=0.013). Statistical significance was attributed to events with a p<0.05.

Conclusion

Quarter laser assisted hatching is a safe, valid, and relatively easy-to-use procedure for thawed blastocysts. Blastocysts that expanded and herniated after quarter laser assisted hatching presented statistically superior results.

Application of femtosecond laser microsurgery in assisted reproductive technologies for preimplantation embryo tagging

Femtosecond laser pulses were applied for precise alphanumeric code engraving on the zona pellucida (ZP) of mouse zygotes for individual embryo marking and their identification. The optimal range of laser pulse energies required for safe ZP microsurgery has been determined. ZP was marked with codes in three different planes to simplify the process of embryo identification. No decrease in developmental rates and no morphological changes of embryos post laser-assisted engraving have been observed. ZP thickness of embryos post laser-assisted code engraving has been shown to differ significantly from that of control group embryos at the hatching stage. Due to moderate ZP thinning as compared to its initial width at 0.5 dpc (days post coitum), readability of the code degrades slightly and it still remains recognizable even at hatching stage. Our results demonstrate that application of femtosecond laser radiation could be an effective approach for noninvasive direct embryo tagging, enabling embryo identification for the whole period of preimplantation development.