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

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.

Clinical and neonatal outcomes of complete zona pellucida removal by laser-assisted hatching after single vitrified-warmed blastocyst transfer

Laser-assisted hatching (LAH) is a widely used and unavoidable technique in assisted reproductive technology after frozen embryo transfer (FET). We aimed to investigate the safety and efficacy of completely ZP (zona pellucida) removed by an assisted laser group compared to an intact group after FET. This retrospective study involved 320 SVBT  single vitrified-warmed blastocyst transfers of 213 patients who underwent clomiphene citrate (CC) based minimal stimulation protocol. This study compared 160 SVBT with ZP that were completely removed using laser-assisted (laser beams of 10-15, a wavelength of 1.48 μm, and duration of 1.8-2.2 ms) to 160 cases of intact SVBT. Fisher's exact test, chi-squared test, and logistic regression are used for statistical analysis. The women's age, cause of infertility, BMI, transferred embryo day, insemination methods, and blastocyst grade were not significantly different between two groups. The implantation rate (66.2% vs. 51.2%, P < 0.01), the clinical pregnancy rate (CPR, 52.5% vs. 39.3%, P = 0.01), and the live birth rate (LBR, 43.7% vs. 29.3%, P < 0.01) were significantly higher in the completely ZP removed than the intact group. In logistic regression analysis, the laser-assisted hatching group showed about 2 times higher implantation rate and CPR and LBR than the control group. But miscarriage, gestational weeks, gender, birth weight, and twin births were insignificant between two groups. Our study suggests ZP free embryo transfer by assisted laser is more effective and safer than intact embryo transfer.

The Current Practice of Assisted Hatching for Embryos in Fertility Centres: a General Survey

At present, there is no standardised protocol for assisted hatching (AH) and the field is beset with contradictory data. We hypothesised that such contradiction may be related to inconsistencies in clinical practice. This study aimed to investigate the application, preferences, and variations of AH in current clinical practice prior to embryo transfer (AHpET) and biopsy (AHpBP). An online voluntary survey, consisted of 25 questions regarding different aspects of AH, was circulated amongst different fertility centres via newsletters between October 2019 and March 2020. One-hundred twenty-nine different fertility centres participated in the survey. AHpBP was widely used (90.6% [48/53]) amongst these centres, especially for trophectoderm biopsy (92.2% [47/51]). In contrast, only 64.6% (73/113) of centres administrated AHpET; the application of AHpET was even lower in UK-based centres (36.6% [15/41]). Although laser pulses have become the predominant technique for AH, significant variation existed in the precise strategy. Zona pellucida (ZP) drilling was the main method for AHpBP, whilst both ZP drilling and ZP thinning were applied equally for AHpET. Furthermore, the ZP manipulation varied widely with regards to the size of the ZP opening and the extension of ZP thinning. This is the first representative survey relating to the current practice of AH. Laser-assisted AH is used extensively, especially for AHpBP. However, there is significant disparity in clinical practice across different centres. Future research should aim to create a standardised protocol for AH to help reduce the evident variation in clinical practice and investigate the true value of AH.

Site specificity of blastocyst hatching significantly influences pregnancy outcomes in mice

Blastocysts hatch from the zona pellucida (ZP) to enable implantation into the uterine endometrial epithelium, but little is known regarding the effect of hatching sites on pregnancy outcomes. Murine hatching embryos were categorized into five groups based on initial trophectoderm projection (TEP)/ZP position corresponding to the inner cell mass center. In blastocysts (3.5 dpc) post-12 hours in vitro culture, TEP rates of A-site (44.4%) and B-site (38.6%) embryos were higher than those of C-site (12.5%) and D-site (3.1%) embryos, while the O-site (1.4%) was the lowest (P < .05). Post-ET A-site (55.6%) and B-site (65.6%) birth rates were higher than those of C-site embryos (21.3%) and controls (P < .05). Furthermore, live birth rate of B-site embryos remained higher than C-site embryos (68.8% vs 31.3%; P < .05) when both were transferred into the same recipients. Different TEP site blastocysts exhibited different implantation competences: the implantation rate of C-site embryos was lower than that of both A- and B-site groups (67.7% vs 84.3% and 83.2%, respectively; P < .05) at 2 days post-ET. C-site embryos also had a distinctly higher ratio of developmental defects (47.5%) than A- and B-site embryos (22.5% and 14.6%, respectively), with implantation failure mainly associated with poor birth rate, a finding corroborated by differential gene expression analysis such as LIF, LIFR, and S100a9. Surprisingly, acidified Tyrode's solution (AAH)-treated B-site blastocysts had a significantly increased birth rate (77.1%) than C-site (55.3%) and controls (43.4%). Site specificity and differential gene expression during embryo hatching can be applied in ART screening. More importantly, assisted hatching by AAH is effective and feasible for improving pregnancy and term development, particularly at the B-site, for humans and in animal husbandry.