Randomized double-blind comparison of laser zona pellucida thinning and breaching in frozen-thawed embryo transfer at the cleavage stage

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.

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.

Assisted hatching on assisted conception (in vitro fertilisation (IVF) and intracytoplasmic sperm injection (ICSI))

BACKGROUND

Failure of implantation and conception may result from inability of the blastocyst to escape from its outer coat, which is known as the zona pellucida. Artificial disruption of this coat is known as assisted hatching and has been proposed as a method for improving the success of assisted conception by facilitating embryo implantation.

OBJECTIVES

To determine effects of assisted hatching (AH) of embryos derived from assisted conception on live birth and multiple pregnancy rates.  SEARCH METHODS: We searched the Cochrane Gynaecology and Fertility Group Specialised Register (until May 2020), the Cochrane Central Register of Controlled Trials (CENTRAL; until May 2020), in the Cochrane Library; MEDLINE (1966 to May 2020); and Embase (1980 to May 2020). We also searched trial registers for ongoing and registered trials (http://www.clinicaltrials.gov - a service of the US National Institutes of Health; http://www.who.int/trialsearch/Default.aspx - The World Health Organization International Trials Registry Platform search portal) (May 2020).

SELECTION CRITERIA

Two review authors identified and independently screened trials. We included randomised controlled trials (RCTs) of AH (mechanical, chemical, or laser disruption of the zona pellucida before embryo replacement) versus no AH that reported live birth or clinical pregnancy data.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures recommended by Cochrane. Two review authors independently performed quality assessments and data extraction.

MAIN RESULTS

We included 39 RCTs (7249 women). All reported clinical pregnancy data, including 2486 clinical pregnancies. Only 14 studies reported live birth data, with 834 live birth events. The quality of evidence ranged from very low to low. The main limitations were serious risk of bias associated with poor reporting of study methods, inconsistency, imprecision, and publication bias. Five trials are currently ongoing. We are uncertain whether assisted hatching improved live birth rates compared to no assisted hatching (odds ratio (OR) 1.09, 95% confidence interval (CI) 0.92 to 1.29; 14 RCTs, N = 2849; I² = 20%; low-quality evidence). This analysis suggests that if the live birth rate in women not using assisted hatching is about 28%, the rate in those using assisted hatching will be between 27% and 34%. Analysis of multiple pregnancy rates per woman showed that in women who were randomised to AH compared with women randomised to no AH, there may have been a slight increase in multiple pregnancy rates (OR 1.38, 95% CI 1.13 to 1.68; 18 RCTs, N = 4308; I² = 48%; low-quality evidence). This suggests that if the multiple pregnancy rate in women not using assisted hatching is about 9%, the rate in those using assisted hatching will be between 10% and 14%. When all of the included studies (39) are pooled, the clinical pregnancy rate in women who underwent AH may improve slightly in comparison to no AH (OR 1.20, 95% CI 1.09 to 1.33; 39 RCTs, N = 7249; I² = 55%; low-quality evidence). However, when a random-effects model is used due to high heterogeneity, there may be little to no difference in clinical pregnancy rate (P = 0.04). All 14 RCTs that reported live birth rates also reported clinical pregnancy rates, and analysis of these studies illustrates that AH may make little to no difference in clinical pregnancy rates when compared to no AH (OR 1.07, 95% CI 0.92 to 1.25; 14 RCTs, N = 2848; I² = 45%). We are uncertain about whether AH affects miscarriage rates due to the quality of the evidence (OR 1.13, 95% CI 0.82 to 1.56; 17 RCTs, N = 2810; I² = 0%; very low-quality evidence).

AUTHORS' CONCLUSIONS

This update suggests that we are uncertain of the effects of assisted hatching (AH) on live birth rates. AH may lead to increased risk of multiple pregnancy. The risks of complications associated with multiple pregnancy may be increased without evidence to demonstrate an increase in live birth rate, warranting careful consideration of the routine use of AH for couples undergoing in vitro fertilisation (IVF) or intracytoplasmic sperm injection (ICSI). AH may offer a slightly increased chance of achieving a clinical pregnancy, but data quality was of low grade. We are uncertain about whether AH influences miscarriage rates.

Higher implantation and live birth rates with laser zona pellucida breaching than thinning in single frozen-thawed blastocyst transfer

While zona pellucida (ZP) breaching of day-3 frozen blastocysts embryos can increase the blastocyst hatching rate, compared with ZP thinning, the pregnancy and implantation rates are similar. The aim of this study was to compare pregnancy outcomes and the risks associated with frozen-thawed blastocysts between laser ZP breaching and laser ZP thinning. For the thinning group, ZP of thawed blastocyst was thinned to a length of 30-40 μm using laser between January 2013 and October 2015. On the other hand, for the breaching group, thawed blastocysts were breached with a 60-80 μm hole in the ZP using laser between November 2015 and April 2018. The implantation rate of ZP breaching (72.7%) was higher than that of ZP thinning (61.8%). In single frozen blastocyst transfer, the implantation rate, clinical pregnancy rate, and live birth rate of ZP breaching (73.9%, 73.9%, 61.8%, respectively) were significantly higher than those of ZP thinning (60.9%, 60.9%, 46.7%, respectively). The abortion rate, preterm birth rate, congenital malformation, birth defects, and birth weight did not significantly differ between the two groups. In conclusion, laser assisted hatching during single frozen blastocyst transfer using ZP breaching exhibit higher implantation, pregnancy, and live birth rates compared with ZP thinning. No significant differences were observed between the two assisted hatching methods in terms of adverse effects on pregnancy and newborns.

Revisiting embryo assisted hatching approaches: a systematic review of the current protocols

Zona pellucida (ZP) manipulation, termed "assisted hatching" (AH), has been introduced in order to favor embryo hatching and ultimately improve assisted reproductive technology success but with poor proofs of safety and biological plausibility. We herein provide a systematic review of clinical outcomes following the application of different methods of ZP manipulation on fresh or frozen/thawed embryos at different developmental stages in different groups of patients. Out of the 69 papers that compared the clinical outcomes deriving from hatched versus non-hatched embryos, only 11 considered blastocysts while the rest referred to cleavage stage embryos. The ZP thinning of fresh embryos either by chemical or laser approach was shown to provide very limited benefit in terms of clinical outcomes. Better results were observed with procedures implying a higher degree of zona manipulation, including zona removal. Studies comparing the mechanical or chemical procedures to those laser-mediated consistently reported a superiority of the latter ones over the former. Literature is consistent for a benefit of ZP breaching in thawed blastocysts. This review provides the current knowledge on the AH procedure in order to improve its efficacy in the appropriate context. Embryologists might benefit from the approaches presented herein in order to improve Assisted Reproduction Technologies (ART) outcomes.

Effect of the site of assisted hatching on vitrified-warmed blastocyst transfer cycles: a prospective randomized study

PURPOSE

To assess the effect of assisted hatching (AH) site on the clinical outcomes in vitrified-warmed blastocyst transfer cycles.

METHODS

A total of 160 women who underwent vitrified-warmed blastocyst transfer cycles were randomized to either the ICM group (AH performing at the site near the inner cell mess, ICM), or the TE group (AH performing at the site opposite to the ICM). AH with laser zona drilling was performed 20 or 30 min after thawing once the ICM can be detected. Clinical pregnancy rate, implantation rate, live birth rate and the occurrence rate of monozygotic twins (MZT) pregnancy after transfer of these two groups were compared.

RESULTS

No significant difference was found in the clinical pregnancy rate (63.8% vs. 67.5%), implantation rate (51.7% vs. 53.6%) and live birth rate (57.5% vs. 62.5%) between the ICM group and the TE group. The occurrence rate of MZT was comparable between the two groups (3.9% vs. 5.6%).

CONCLUSIONS

The site of assisted hatching has no influence on the implantation, pregnancy and live birth rate in human vitrified-warmed blastocyst transfer cycles.

Effects of partial or complete laser-assisted hatching on the hatching of mouse blastocysts and their cell numbers

BACKGROUND

It is still debatable whether a full-thickness assisted hatching (AH) is better than the partial zona thinning. In this research, we used a mouse model to study the effect of partial and complete laser-AH on the rate of completely hatched blastocyst and their cell numbers.

METHODS

In experiment 1, mouse morulae had 0, 1, 2 or 3 full-thickness openings of 10 microns created in the zona pellucida with an infrared laser beam. In the second experiment, 0, 1 and 2 openings of 20 microns were studied. In the third experiment, a full-thickness opening of 20 microns or quarter-thinning of the zonal circumference to a depth of 90% was compared with non-AH controls.

RESULTS

No difference in blastocyst formation was found in laser-treated groups and in the controls. In experiment 1, the rate of completely hatched blastocysts was significantly lower than the controls. In experiment 2 when the size of the opening was increased, blastocysts completely hatched at a significantly higher rate than that in the controls. In experiment 3, the rate of completely hatched blastocysts was the highest in the full-thickness group. Cell numbers in completely hatched blastocysts from both AH groups were significantly fewer than those in the controls.

CONCLUSIONS

Full-thickness opening resulted in a higher rate of completely hatched blastocysts than quarter zonal-thinning and controls, but the cell numbers were significantly decreased.

Assisted hatching on assisted conception (in vitro fertilisation (IVF) and intracytoplasmic sperm injection (ICSI)

BACKGROUND

Failure of implantation and conception may result from an inability of the blastocyst to escape from its outer coat, which is known as the zona pellucida. Artificial disruption of this coat is known as assisted hatching and has been proposed as a method for improving the success of assisted conception by facilitating embryo implantation.

OBJECTIVES

To determine the effect of assisted hatching (AH) of embryos from assisted conception on live birth and multiple pregnancy rates. 

SEARCH METHODS

We searched the Cochrane Menstrual Disorders and Subfertility Group Specialised Register (August 2012), the Cochrane Central Register of Controlled Trials (CENTRAL) (August 2012), MEDLINE (1966 to August 2012) and EMBASE (1980 to August 2012).

SELECTION CRITERIA

Three authors identified and independently screened trials. We included randomised controlled trials (RCTs) of AH (mechanical, chemical or laser disruption of the zona pellucida prior to embryo replacement) versus no AH that reported live birth or clinical pregnancy.

DATA COLLECTION AND ANALYSIS

Three authors independently performed quality assessments and data extraction.

MAIN RESULTS

Thirty-one trials reported clinical pregnancy data, including 1992 clinical pregnancies in 5728 women. There was no significant difference in the odds of live birth in the AH group compared with the control group (9 RCTs; odds ratio (OR) 1.03, 95% confidence interval (CI) 0.85 to 1.26, moderate quality evidence), with no evidence of significant heterogeneity (P = 0.38) or inconsistency (I(2) = 6%). Analysis of the clinical pregnancy rates from the nine studies which reported live birth showed a non-significant result (OR 1.03, 95% CI 0.85 to 1.25 ).Analysis of all of the studies included in this update (31 RCTs) showed that the clinical pregnancy rate in women who underwent AH was slightly improved, but the level only just reached statistical significance (OR 1.13, 95% CI 1.01 to 1.27, moderate quality evidence). However, it is important to note that the heterogeneity for this combined analysis for clinical pregnancy rate was statistically significant (P = 0.001) and the I(2) was 49%. Subgroup analysis of women who had had a previous failed attempt at IVF found improved clinical pregnancy rates in the women undergoing AH compared with the women in the control group (9 RCTs, n = 1365; OR 1.42, 95% CI 1.11 to 1.81) with I(2) = 20%. Miscarriage rates per woman were similar in both groups (14 RCTs; OR 1.03, 95% CI 0.69 to 1.54, P = 0.90, moderate quality evidence). Multiple pregnancy rates per woman were significantly increased in women who were randomised to AH compared with women in the control groups (14 RCTs, 3447 women; OR 1.38, 95% CI 1.11 to 1.70, P = 0.004, low quality evidence).

AUTHORS' CONCLUSIONS

This update has demonstrated that whilst assisted hatching (AH) does appear to offer a significantly increased chance of achieving a clinical pregnancy, the extent to which it may do so only just reaches statistical significance. The 'take home' baby rate was still not proven to be increased by AH. The included trials provided insufficient data to investigate the impact of AH on several important outcomes. Most trials still failed to report on live birth rates.

Relevance of assisted hatching in an oocyte donation programme using egg cryobanking: a prospective randomised study

OBJECTIVE

The objective of this prospective randomised study was to evaluate if there is an improvement in clinical outcomes when assisted hatching (AH) is performed in embryos derived from vitrified/warmed oocytes in an ovum donation programme using egg cryobanking.

STUDY DESIGN

Sixty oocyte recipients in a donation programme using egg cryobanking were randomly allocated to the assisted hatched (AH, n=30) or control group (n=30). The pregnancy and implantation rates were compared between the groups.

RESULTS

A total of 288 vitrified oocytes were warmed for the 60 recipients. Of the 288 vitrified oocytes, 94.8% survived. All surviving oocytes were sperm injected, and 83.5% underwent fertilisation. There were 172 good-quality embryos selected for transfer. The total pregnancy rate was 40%. The pregnancy rate did not differ between the AH and control groups (43.3% and 33.3%, respectively, p=0.1967), but AH resulted in a higher implantation rate (31.6% vs. 18.4%, p=0.0206).

CONCLUSION

Our study demonstrates the effectiveness of AH in embryos derived from warmed oocytes. Our results also suggest that oocyte cryopreservation can be considered as a tool for providing highly successful outcomes in an egg donor programme.

A comparative analysis of the zona pellucida birefringence of fresh and frozen–thawed human embryos

The cryopreservation of human embryos is thought to induce alteration in the glycoprotein matrix and lead to zona change. However, this assumption has been full of controversies till now. The objective of this study was to evaluate the effect of cryopreservation on zona pellucida of human embryos. Fresh (n=106, from 40 patients) and frozen–thawed embryos (n=123, from 40 patients) were obtained from consenting patients who received conventional IVF and ICSI treatment. The birefringence of zona pellucida in human fresh and frozen–thawed embryos was imaged and quantitatively analyzed using polarized light microscopy before embryo transfer. There was no significant difference in retardance and thickness of the zona pellucida multilaminar structure between the two groups. Pregnancy and implantation rates of transferred fresh and frozen–thawed embryos were also compared. No significant difference was found in the rates of clinical pregnancy (47.5 vs 37.5%) and implantation (24.5 vs 23.2%) between the two groups. This study suggests that there is no significant change in the zona pellucida birefringence of human embryos before and after cryopreservation.

Impact of the size of zona pellucida thinning area on vitrified-warmed cleavage-stage embryo transfers: a prospective, randomized study

PURPOSE

The aim of this study was to determine if the size of zona pellucida thinning area by laser assisted hatching could affect the rates of pregnancy and implantation for vitrified-warmed embryo transfers at the cleavage-stage.

METHODS

A total of 120 vitrified-warmed cleavage-stage embryo transfers were randomly assigned to either quarter or half of zona pellucida thinning group.

RESULTS

The rates of clinical pregnancy (46.7 versus 25.0%) and implantation (32.0 versus 16.2%) were significantly greater in the half thinning group than in the quarter thinning group (P = 0.0218 and P = 0.0090, respectively).

CONCLUSIONS

The results of this investigation show that, in vitrified-warmed embryo transfers at the cleavage-stage, the size of zona pellucida thinning area by laser assisted hatching impacts the rate of clinical pregnancy and implantation and that half of zona pellucida thinning significantly increases both of these results compared with quarter of zona pellucida thinning.