Laser assisted zona hatching does not lead to immediate impairment in human embryo quality and metabolism

Exploring the benefit of different methods to perform assisted hatching in the ART laboratory: A narrative review

In the last decades, to enhance success rates in assisted reproductive technology (ART) cycles, scientists have continually tried to optimize embryo culture and selection to increase clinical outcomes. In this scenario, the application of laser technology has increased considerably worldwide and is currently applied across ART in several ways: for assisted hatching (AH) or thinning of the zona pellucida (ZP), embryo biopsy, to immobilize and select the sperm during intracytoplasmic sperm injection, as well as to induce artificial blastocyst shrinkage before cryopreservation. Laser-AH has been suggested as a procedure to improve embryo implantation: the concept is that drilling holes through or thinning of the ZP could improve the hatching process and implantation. The artificial disruption of the ZP can be performed by different approaches: mechanically, chemically and with the laser, which is one of the most favourable and easy methods to remove part of the ZP and to augment the possibilities of implantation in patients defined as having a poor prognosis of success, or when the ZP is too thick. However, in the current literature, there is not sufficient evidence about the potential risk or impairment that laser utilization might induce on embryo development; therefore, the main aim of the current review is to provide an overview of the existing knowledge on the ZP and the mechanisms of manipulating it to improve the effectiveness of ART. Also, it emphasizes the positive aspect of laser application as a powerful tool that might increase the chance of pregnancy for infertile couples undergoing ART cycles.

Two laser-assisted hatching methods of embryos in ART: a systematic review and meta-analysis

BACKGROUND

Laser-assisted hatching (LAH) stands as the predominant technique for removing the zona pellucida (ZP) in embryos, primarily consisting of two methods: drilling laser-assisted hatching (D-LAH) and thinning laser-assisted hatching (T-LAH). Presently, both methods have limitations, and their comparative efficacy for embryo implantation and clinical pregnancy remains uncertain.

AIM

Evaluate the impact of D-LAH and T-LAH on clinical pregnancy rates within assisted reproductive technology (ART).

METHODS

We systematically searched electronic databases including PubMed, Web of Science, and Cochrane Library until July 20, 2022. This study encompassed observational studies and randomized controlled trials (RCTs). A 95% confidence interval (CI) was utilized for assessing the risk ratio (RR) of pregnancy outcomes. The level of heterogeneity was measured using I2 statistics, considering a value exceeding 50% as indicative of substantial heterogeneity.

RESULTS

The meta-analysis scrutinized 9 studies involving 2405 clinical pregnancies from D-LAH and 2239 from T-LAH. Findings suggested no considerable variation in the clinical pregnancy rates between the two techniques (RR = 0.93, 95% CI: 0.79-1.10, I2 = 71%, P = 0.41). Subgroup analyses also revealed no substantial differences. However, D-LAH exhibited a notably higher occurrence of singleton pregnancies compared to T-LAH (RR = 2.28, 95% CI: 1.08-4.82, I2 = 89%, P = 0.03). There were no noteworthy distinctions observed in other secondary outcomes encompassing implantation rate, multiple pregnancies, ongoing pregnancy, miscarriage, premature birth, and live birth.

CONCLUSION

Both the primary findings and subgroup analyses showed no marked variance in clinical pregnancy rates between D-LAH and T-LAH. Therefore, patients with varying conditions should select their preferred LAH technique after assessing their individual situation. However, due to the restricted number of studies involved, accurately gauging the influence of these laser techniques on clinical outcomes is challenging, necessitating further RCTs and high-quality studies to enhance the success rate of ART.

TRIAL REGISTRATION

PROSPERO: CRD42022347066.

Assisted Hatching Treatment of Piezo-Mediated Small Hole on Zona Pellucida in Morula Stage Embryos Improves Embryo Implantation and Litter Size in Mice

For in vitro produced embryos generated from in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) procedure, the intra- and extra-environmental factors during in vitro culture have significant impact on latter embryo development and fetus growth. Assisted hatching (AH), an effective approach to facilitate hatchability for in vitro generated embryos, is an essential step for successful embryo implantation in the uterus. However, regarding the different AH methods reported in clinical practice, it is still unknown whether zona pellucida (ZP) broken is based on AH applied in diverse stages of embryos affect implantation and fetal development. Here, piezo-mediated AH treatments were classified into four categories: (1) drilling one small hole (SH) with a diameter of 10 μm on ZP (SH); (2) drilling one large hole (LH) with a diameter of 40 μm on ZP (LH); (3) made a small area with diameter of 40-μm thinner on ZP [small area thinner (ST)]; (4) made a large area with a diameter of 80-μm thinner [large area thinner (LT)]. These four AH treatments were applied in different stage embryos including two-cell, four-cell, and morula. The most efficient AH approach was chosen according to the final hatch rate at 120 h after fertilization. We found that the approach of SH applied in morula-stage embryos obtained the highest hatch rate. To further investigate if this treatment has any side effect on later development after embryo transfer, we evaluated embryo implantation, gestational period, litter size, and growth. Our results showed that SH applied in morula-stage embryos could facilitate the implantation process and increase litter size. Meanwhile, this approach had no side effect on birth weight, growth, or gender ratio in the offspring. We conclude that drilling a SH on ZP in morula-stage embryos is an effective and reliable AH approach for in vitro cultured embryos in rodent. And this approach is worth further investigating in human-assisted reproductive technology.

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.

Obstetric and neonatal outcomes after frozen-thawed embryos transfer with laser-assisted hatching: a retrospective cohort study

PURPOSE

To ascertain if assisted hatching (AH) increases the risk of placenta-associated diseases and perinatal outcomes after frozen-thawed cleavage-stage embryo transfer.

METHODS

We retrospectively evaluated 924 women who conceived with frozen-thawed cleavage-stage embryos transfer with (n = 390) or without (n = 534) laser-AH between 2013 and 2015. Data were obtained from the database on in vitro fertilization (IVF) patients in Shanghai First Maternity and Infant Hospital. We assessed neonatal (preterm birth, low birthweight, fetal macrosomia, stillbirth) and obstetric (miscarriage, ectopic pregnancy, post-term pregnancy, gestational diabetes (GDM), preeclampsia, intrahepatic cholestasis (ICP), placenta previa, placental abruption, premature rupture of membranes) outcomes.

RESULTS

In twins, the median birthweight was lower in the AH group than that in the control group, and the prevalence of low birthweight (< 2500 g) was significantly higher in the AH group; after adjusting for maternal age, body mass index, mode of fertilization, and parity, no significant difference was found. In twins, no significant difference was detected in the prevalence of stillbirth or preterm pregnancy. In singleton births, there was no significant difference in the prevalence of low birthweight, macrosomia, preterm pregnancy or post-term pregnancy between the two groups. In singletons and twins, there were no significant differences in the prevalence of miscarriage, ectopic pregnancy, preeclampsia, GDM, ICP, or placenta abruption between the two groups.

CONCLUSIONS

AH is a relatively safe method and our study provides important information for using this method in carefully selected patients.

Rapid nuclear magnetic resonance data acquisition with improved resolution and sensitivity for high-throughput metabolomic analysis

Nuclear magnetic resonance (NMR)-based metabolomics has witnessed rapid advancements in recent years with the continuous development of new methods to enhance the sensitivity, resolution, and speed of data acquisition. Some of the approaches were earlier used for peptide and protein resonance assignments and have now been adapted to metabolomics. At the same time, new NMR methods involving novel data acquisition techniques, suited particularly for high-throughput analysis in metabolomics, have been developed. In this review, we focus on the different sampling strategies or data acquisition methods that have been developed in our laboratory and other groups to acquire NMR spectra rapidly with high sensitivity and resolution for metabolomics. In particular, we focus on the use of multiple receivers, phase modulation NMR spectroscopy, and fast-pulsing methods for identification and assignments of metabolites.

A comparison of the clinical effects of thinning and drilling on laser-assisted hatching

To systematically investigate the effects of two methods used for laser-assisted hatching (LAH) on clinical outcomes after day 4 (D4) on frozen-embryo-transfer (FET) cycles. Data from 11471 infertile patients who underwent FET cycles between January 2014 and October 2018 was retrospectively analyzed. The 1410 patients who met the inclusion criteria were further categorized into two groups based on the hatching procedure used: the thinning laser-assisted hatching group (T-LAH, 716 patients), and the drilling laser-assisted hatching group (D-LAH, 694 patients). The baseline characteristics of the patients were consistent between the two groups. However, the rates of implantation and clinical pregnancy were significantly higher in the T-LAH group compared to the D-LAH group (32.73% vs. 29.09%, P < 0.01, and 50.98% vs. 43.95%, P < 0.01). The proportion of live birth was also higher in the T-LAH group, but the difference was insignificant (39.11% vs. 36.89%, P > 0.05). Moreover, there were no significant differences in rates of miscarriages, multiple pregnancies, ectopic pregnancies, preterm births, and congenital disabilities between the two groups. Nonetheless, significantly higher rates of implantation and pregnancy were reported in the T-LAH group compared to the D-LAH group among patients aged <35 years, patients with at least one previously failed cycle, and patients with an endometrial thickness of 8-10 mm. T-LAH is superior to D-LAH in improving clinical implantation and pregnancy outcomes in D4 FET, particularly in patients aged <35 years with at least one previously failed cycle or an endometrial thickness of 8-10 mm. The findings of this study provide theoretical support for clinical individualized diagnosis and treatment of patients with infertility.

The utility of nuclear magnetic resonance spectroscopy in assisted reproduction

Infertility affects approximately 15-20% of individuals of reproductive age worldwide. Over the last 40 years, assisted reproductive technology (ART) has helped millions of childless couples. However, ART is limited by a low success rate and risk of multiple gestations. Devising methods for selecting the best gamete or embryo that increases the ART success rate and prevention of multiple gestation has become one of the key goals in ART today. Special emphasis has been placed on the development of non-invasive approaches, which do not require perturbing the embryonic cells, as the current morphology-based embryo selection approach has shortcomings in predicting the implantation potential of embryos. An observed association between embryo metabolism and viability has prompted researchers to develop metabolomics-based biomarkers. Nuclear magnetic resonance (NMR) spectroscopy provides a non-invasive approach for the metabolic profiling of tissues, gametes and embryos, with the key advantage of having a minimal sample preparation procedure. Using NMR spectroscopy, biologically important molecules can be identified and quantified in intact cells, extracts or secretomes. This, in turn, helps to map out the active metabolic pathways in a system. The present review covers the contribution of NMR spectroscopy in assisted reproduction at various stages of the process.

Effects of laser zona thinning and artificial blastocoel collapse on the cryosurviving and hatching of buffalo (Bubalus bulalis) blastocysts of different ages

The objectives of this study were to investigate whether blastocoel collapse before vitrification induced by laser improves the cryo-survivability of buffalo in-vitro-fertilized (IVF) blastocysts and whether laser assisted hatching (LAH) promotes hatchability of fresh and frozen-thawed IVF blastocysts. The expanded blastocysts were harvested on Days 6-9 and randomly allocated into five groups as follows: (1) blastocysts were vitrified and thawed without any treatment; (2) blastocysts were vitrified after 15-20 μm zona pellucida (ZP) thinning opposite to the inner cell mass, and blastocoels were also blotted in order to outflow the blastocoelic fluid before vitrification; (3) ZP thinning was made immediately after thawing; (4) fresh blastocysts underwent LAH; and (5) as a control, fresh blastocysts without treatment. Results of the present study showed that the cryosurvival rates of vitrified Day 8 and Day 9 blastocysts in Group 2 were significantly (P < 0.01) higher in Group 2 than Group 1. The hatching rates of Day 8 and Day 9 blastocysts in Group 2 and Group 3 were also significantly (P < 0.01) higher compared with Group 1. Moreover, the hatching rate of Day 9 blastocysts in Group 4 was notably (P < 0.05) higher than Group 5. In conclusion, LAH promotes the hatching rates of Day 9 fresh and Days 8-9 vitrified blastocysts, and artificial blastocoel collapse before vitrification improves the cryosurvival rate of Days 8-9 IVF buffalo blastocysts.

Laser-assisted cell removing (LACR) technology contributes to the purification process of the undifferentiated cell fraction during pluripotent stem cell culture

Purification of undifferentiated cells by removing differentiated parts is an essential step in pluripotent stem cell culture. This process has been traditionally performed manually using a fine glass capillary or plastic tip under a microscope, or by culturing in a selective medium supplemented with anti-differentiation inhibitors. However, there are several inevitable problems associated with these methods, such as contamination or biological side-effects. Here, we developed a laser-assisted cell removing (LACR) technology that enables precise, fast, and contact-less cell removal. Using LACR combined with computational image recognition/identification-discriminating technology, we achieved automatic cell purification (A-LACR). Practicability of A-LACR was evaluated by two demonstrations: selective removal of trophoblast stem (TS) cells from human iPS and TS cell co-cultures, and purification of undifferentiated iPS cells by targeting differentiated cells that spontaneously developed. Our results suggested that LACR technology is a novel approach for stem cell processing in regenerative medicine.

Epigenetic changes in preimplantation embryos subjected to laser manipulation

The advantage of using laser for assisted hatching in routine assisted reproductive technology (ART) practice is debatable. Recently, it has been shown that laser-manipulated mouse embryos had compromised genetic integrity. However, the impact of laser-assisted hatching (LAH) on the epigenetic integrity of the preimplantation embryos is not elucidated so far. Since continuous thermal stress on embryos was found to lower mRNA levels of de novo (bovine) methyl transferases in embryos, we hypothesize that thermal energy induced during LAH may alter the epigenetic signature through abnormal de novo methyl transferases (Dnmts) levels. Thus, using mouse model, we made an attempt to look into the expression of Dnmt3a and Dnmt3b in laser-manipulated embryos and their effects on global methylation. This experimental prospective study used mouse embryos from varying developmental stages (2-cell, 6-8-cell, and blastocyst) which were subjected to LAH using a 1480-nm diode laser. Two pulses of 350 μs frequency were applied to breach the zona pellucida, and then, embryos were assessed for the expression of two de novo methyl transferases (Dnmt3a and Dnmt3b) and LINE-1 (long interspersed element-1) methylation when LAH embryos developed to blastocyst stage. Results from this study have shown that blastocysts subjected to LAH at two-cell stage had significantly lower mRNA transcripts of Dnmt3a (P < 0.01) and Dnmt3b (P < 0.05) whereas LAH at six- to eight-cell and blastocyst stages did not affect the mRNA level significantly. On the other hand, LINE-1 methylation did not change significantly between LAH and control group in all the stages studied. These results suggest that two-cell-stage laser manipulation of embryos changes the mRNA level of Dnmts without affecting the global DNA methylation.

SOFAST-HMQC-an efficient tool for metabolomics

Nuclear magnetic resonance (NMR)-based metabolomics relies mostly on 1D NMR; however, the technique is limited by overlap of the signals from the metabolites. In order to circumvent this problem, 2D ¹H-¹³C correlation spectroscopy techniques are often used. However owing to poorer natural abundance and gyromagnetic ratio of ¹³C, the acquisition time for 2D ¹H-¹³C heteronuclear single quantum coherence spectroscopy (HSQC) is long. This makes it almost impossible to be used in high throughput study. We have reported the application of selective optimized flip angle short transient (SOFAST) technique coupled to heteronuclear multiple quantum correlation (HMQC) along with nonlinear sampling (NUS) in urine and serum samples. This technique takes sevenfold less experimental time than the conventional ¹H-¹³C HSQC experiment with retention of almost all molecular information. Hence, this can be used for high throughput study. Graphical abstract SOFAST-HMQC is a two-dimensional NMR technique that significantly decreases experimental time without loss of information. This technique is applied in complex biofluid samples that are used for high throughput metabolomics studies and shows promise of better information recovery than conventional two-dimensional NMR technique in shorter time.