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

Following the guidelines outlined in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA), this study performed a thorough analysis employing both quantitative and qualitative methodologies [25].

Electronic sources, including PubMed, Web of Science, and Cochrane Library, were reviewed until July 20, 2022. The following medical topic header (MeSH) phrases and/or keywords are primarily used for retrieval: ((assisted hatching) AND (zona pellucida)), ((thinning and drilling) AND (assisted hatching)), ((thinning and opening) AND (assisted hatching)), ((thinning and breaching) AND (assisted hatching)). Two reviewers (C.K. and H.Z.) conducted a literature search that yielded a total of 491 studies. After applying exclusion criteria using EndNote, 209 studies met the requirements for quantitative analysis. These studies were selected based on the reviewers' evaluation of the titles, abstracts, and full texts of the remaining 205 studies [12, 16, 23, 24, 26‐30]. The literature search specifically focused on English papers, as depicted in Fig. 1, which outlines the retrieval and inclusion process.

During the literature screening process, the inclusion and exclusion standards for the studies are determined by reading and evaluating their significance. Two reviewers (C.K. and H.Z.) separately filter the literature during the literature screening process, and a third reviewer judges the contentious pieces (Y.J).

Inclusion criteria:

Exclusion criteria:

To avoid overlooking relevant research, two evaluators (C.K. and H.Z.) conducted independent studies using specified keywords and MeSH. The evaluators (C.K. and H.Z.) extracted data from the studies, and any contentious findings were reexamined by a third reviewer (Y.J.) before the authors reached a consensus.

Two evaluators (C.K. and H.Z.) assessed the quality of the literature, while a third reviewer (Y.J.) resolved any ambiguities. The Cochrane risk-of-bias tool and Newcastle Ottawa Scale (NOS) were selected for quality evaluation since the research included both RCTs and non-RCTs [31]. The Cochrane risk-of-bias tool primarily assesses RCTs, covering elements such as random sequence generation, allocation concealment, blinding of participants and personnel, blinding of outcome assessment, incomplete outcome data, selective reporting, and other biases. On the other hand, the Newcastle–Ottawa Scale (NOS) is tailored for evaluating bias in non-RCTs its main entries include: is the case definition adequate; representativeness of the cases; selection of controls; definition of controls; Comparability of cases and controls on the basis of the design or analysis; ascertainment of exposure; Same method of ascertainment for cases and controls; non-response rate. Publication bias is appraised through funnel charts.

Review Manager version 5.4 (The Cochrane Collaboration) was used for meta-analysis. Both main and secondary outcomes are considered in statistical analysis. The risk ratio (RR) of pregnant result was examined using a 95% confidence interval (CI). Heterogeneity was measured by I². The study is regarded as extremely heterogeneous when I² > 50% [32]. Given the diverse population sources in each study resulting in considerable variability, the random-effects model was chosen for analysis.

A comprehensive search was conducted across PubMed, Web of Science, and the Cochrane library, resulting in a total of 491 studies. Using EndNote 20, 205 duplicate studies were removed, leaving 286 studies for title and abstract screening. Following this screening process, 264 studies were excluded. The complete texts of the remaining 22 studies were thoroughly read, resulting in the selection of 9 studies for qualitative and quantitative analysis. The diagram in Fig. 1 depicted the complete filtering procedure. Nine studies totaling 4 RCT [16, 28‐30] and 5 non-RCT [12, 23, 24, 26, 27] were included. The particular information traits that were examined are listed in Table 1.

In this meta-analysis, we conducted an evaluation of 4 RCTs using the Cochrane risk-of-bias assessment. We assessed various sources of bias including selection bias, performance bias, detection bias, attrition bias, reporting bias, and other potential biases by examining key factors such as random sequence generation, allocation concealment, blinding of participants and personnel, blinding of outcome assessment, incomplete outcome data, and selective reporting. The results indicated a relatively low and unclear risk (Supplementary Fig. S1a). We used NOS to evaluate the risk of 5 non-RCTs, and all included studies scored ≥ 4, indicating medium-quality studies (Supplementary Fig. S 1b).

Clinical pregnancy included a total of 9 trials. The outcome revealed no discernible variation between D-LAH and T-LAH (RR = 0.93, 95% Cl: 0.79—1.10, I² = 71%, P = 0.41, Table 2 and Fig. 2a). We performed a subgroup study on the blastocysts for auxiliary hatching, both fresh and frozen, and the findings revealed no discernible differences between D-LAH and T-LAH (5 studies) (RR = 0.83, 95% Cl: 0.56—1.23, I² = 74%, P = 0.36, Table 2 and Fig. 2b) (4 studies) (RR = 0.97, 95% Cl: 0.81—1.16, I² = 74%, P = 0.71, Table 2 and Fig. 2c). Then we analyzed the RCT (4 studies) (RR = 0.98, 95% Cl: 0.72—1.33, I² = 42%, P = 0.90, Table 2 and Fig. 2d) and non-RCT (5 studies) (RR = 0.91, 95% Cl: 0.73—1.12, I² = 83%, P = 0.36, Table 2 and Fig. 2e), and the results still had no significant difference.

The outcomes of the 6 studies on blastocyst implantation revealed no significant differences between D-LAH and T-LAH. (RR = 1.02, 95% Cl: 0.80—1.28, I² = 89%, P = 0.89, Table 2 and Fig. 3).

The findings of two singleton pregnancy investigations revealed that D-LAH had a greater singleton pregnancy incidence than T-LAH (RR = 2.28, 95% Cl: 1.08—4.82, I² = 89%, P = 0.03, Table 2 and Fig. 4a). However, there was no significant difference in multiple pregnancies (7 studies) (RR = 0.76, 95% Cl: 0.25—2.29, I² = 94%, P = 0.62, Table 2 and Fig. 4b).

In 4 studies of ongoing pregnancy, the results showed that there was no significant difference between D-LAH and T-LAH (RR = 1.25, 95% Cl: 0.89—1.77, I² = 54%, P = 0.20, Table 2 and Fig. 5).

All studies' findings for miscarriage (5 studies), preterm birth (2 studies), and live birth (3 studies) revealed no discernible difference between D-LAH and T-LAH. (RR = 0.77, 95% Cl: 0.58—1.03, I² = 0%, P = 0.07, Table 2 and Fig. 6a) (RR = 0.92, 95% Cl: 0.46—1.84, I² = 26%, P = 0.82, Table 2 and Fig. 6b) (RR = 0.93, 95% Cl: 0.79—1.09, I² = 63%, P = 0.37, Table 2 and Fig. 6c).

The meta-analysis results showed no significant difference in clinical pregnancy rates between D-LAH and T-LAH for AH. Further subgroup analysis based on fresh or frozen embryos and study type also revealed no significant differences. Overall, the LAH method didn't significantly affect clinical pregnancy outcomes. However, D-LAH showed a higher rate of singleton pregnancies compared to other methods, though no other remarkable distinctions were evident. D-LAH might benefit singleton transplantation, but further research is necessary to validate this. Additionally, we conducted an analysis of multiple pregnancies an initial analysis aimed to assess the heterogeneity of multiple pregnancies. It was found that the study conducted by Chengjun Liu et al. [23] were excluded due to There is a large difference in the number of samples between D-LAH and T-LAH and lack of information regarding patients' abortion history, and the quality of embryo transfer. Consequently, the heterogeneity decreased from 94 to 41%. Nonetheless, there was still no significant distinction observed between D-LAH and T-LAH in terms of their effects (RR = 1.25, 95% Cl: 0.78—2.00, I2 = 41%, P = 0.36). There was no significant difference between D-LAH and T-LAH in ongoing pregnancy, miscarriage, preterm birth and live birth. Whether the embryo can be successfully implanted into clinical pregnancy, what is more important is the interaction between mother and fetus, intimal environment, embryo quality and so on [33]. Therefore, LAH is the factor affecting embryonic pregnancy, but it is not the only factor. The heterogeneity analysis of the primary and secondary outcomes is presented in Supplementary Fig. S2.

No notable differences were found in clinical pregnancy, implantation rate, or live birth between the T-LAH and D-LAH techniques. However, D-LAH notably demonstrated a higher rate of singleton pregnancies than T-LAH. Additionally, following assisted hatching during cleavage, D-LAH showed a greater incidence of blastocyst formation compared to T-LAH [34, 35]. Based on this research, D-LAH may be recommended for clinical use. Nevertheless, considering variations among embryo laboratories and patient populations, the choice of LAH method should align with specific conditions. According to a research by Wang et al. [12], T-LAH had a superior clinical result than D-LAH for patients under 35 with a history of IVF/ICSI failure or 8-10mm endometrial thickness. Additionally, factors such as embryo freezing and freshness, embryo quality, and culture medium were identified to influence ART outcomes [6]. Successful implantation requires synchronized development of both the embryo and endometrium, enabling the expression and secretion of various factors that enhance clinical outcomes by facilitating attachment to the endometrium through the ZP [36]. While D-LAH outperforms T-LAH in singleton pregnancy, no significant differences were observed in other aspects. Therefore, patients with varying conditions should select their preferred LAH technique after assessing their individual situation.

The debate surrounding the two LAH methods for achieving clinical pregnancy persisted [37, 38]. Some studies indicate positive clinical pregnancy outcomes for T-LAH [26], while others report contrary findings or observe no significant differences between the two techniques [23, 24]. This study aimed to evaluate the impact of different LAH techniques on ART outcomes and propose clinical recommendations. Our findings suggest a potential superiority of D-LAH over T-LAH specifically in singleton pregnancies, offering insights for clinical decision-making.

However, the study's low quality necessitates further robust RCT studies for conclusive evidence. However, certain limitations remain in this study. Firstly, the analysis incorporated a limited number of studies. Among the 9 studies evaluating clinical pregnancy outcomes, none explored critical indicators such as blastocyst formation rate, implantation rate, or live birth rate. Subsequent investigations should prioritize assessing the impact on live births. Secondly, significant heterogeneity was identified through a heterogeneity analysis, likely stemming from differences in sample sizes and experimental settings across studies. Thirdly, discrepancies in patient inclusion and exclusion criteria across studies might influence clinical outcomes, considering factors like endometrial thickness, uterine condition, and embryo quality critically impact embryo development and clinical outcomes. Lastly, the study did not address whether assisted reproductive technology contributes to an increased incidence of monozygotic twins, a significant concern in this field. Therefore, more RCTs and high-quality studies are imperative to enhance understanding in this field.