Comparison of Assisted Hatching Techniques and Their Impact on Clinical Pregnancy Outcomes with Optimization Strategies in In Vitro Fertilization

ABSTRACT

Background:

Infertility is a prevalent reproductive issue, often requiring assisted reproductive techniques (ART) such as in vitro fertilization (IVF). Implantation failure remains a major challenge, especially in women of advanced maternal age, those with previous IVF failures, or embryos with a thick zona pellucida. Assisted hatching (AH) is a technique designed to improve implantation rates by facilitating embryo hatching. However, its effectiveness remains uncertain, particularly concerning live birth rates.

Objectives:

This study aims to evaluate the impact of assisted hatching techniques—laser hatching and mechanical hatching—on clinical pregnancy outcomes and implantation success in women with advanced maternal age, recurrent IVF failures, or embryos with a thick zona pellucida. The study also seeks to compare these techniques with a control group receiving no AH.

Methodology:

A total of 180 participants will be divided into three groups: laser hatching, mechanical hatching, and a control group (no assisted hatching), with 60 participants in each group. Embryos will be assessed for suitability, and AH will be performed using laser or mechanical techniques. Following embryo transfer, clinical pregnancy outcomes and implantation rates will be monitored and compared across the groups.

Expected Results:

It is anticipated that assisted hatching, particularly laser-assisted hatching, will lead to higher implantation and clinical pregnancy rates compared to the control group. The study aims to establish whether AH can significantly enhance IVF success in specific patient populations.

Study Implications:

Findings from this research could provide valuable insights into optimizing assisted hatching techniques for improving IVF outcomes. If AH proves beneficial, it may be recommended as a standard adjunct in ART, particularly for high-risk patient groups. Additionally, the study will contribute to understanding the limitations and cost-effectiveness of AH in clinical practice.

INTRODUCTION

Infertility can be defined as an inability of a couple to conceive after 12 or more months of regular unprotected sexual intercourse.[1] Implantation is a very well-ordered process in which the uterus and a competent blastocyst interacts with one another. According to natural fecundity, two-thirds of lost pregnancies occur due to failure of implantation and conception chances are relatively lower (30%) per cycle.[2] Infertility is mainly of two types, primary and secondary. When the pregnancy is never achieved by a person, it is said to be infertility and if one prior pregnancy is achieved, then it is called secondary infertility.[3]

Repeated implantation failure (RIF) is said when the embryos we transfer fail to implant after many cycles of IVF treatment. When menstrual cycles arrive, the endometrium undergoes many physiological and biological changes which help the embryo to implant properly. This important stage lasts for a few days and is called “window of implantation”, because this endometrium wall must be increased in thickness and proliferate so that it can respond to progesterone and become receptive.[4] Zona pellucida present around the oocytes, and unfertilized eggs mark the presence of fertility in females.[5] Women who are 35 and older often face lower chances of successful implantation for several reasons: egg quality affects as women increase by age, their eggs can become fewer and lower in quality, which may lead to more genetic problems.[6] This can affect how well the uterine lining is prepared to support a fertilized egg.

Assisted hatching (AH) is an adjunctive technique used during in vitro fertilization (IVF) procedures to support embryo development. This method involves creating a small opening in the zona pellucida, the outer protective layer of the embryo. By facilitating this opening, AH helps the expanded blastocyst escape its shell a critical step known as hatching.[6] This improved hatching ability is believed to enhance implantation rates when the embryo is transferred to the uterus. In certain cases, the zona pellucida may be too thick or rigid, hindering the embryo’s ability to hatch and attach to the uterine lining effectively. Overall, AH represents a promising strategy for enhancing IVF outcomes, particularly for individuals who have faced difficulties in achieving pregnancy.

AIM

To compare AH techniques for evaluating the impact on clinical pregnancy and optimizing methods in IVF.

OBJECTIVE

1. To investigate how AH affects embryo development and its association with clinical pregnancy

2. To access embryo implantation rates in the uterus, thereby elevating successful pregnancy outcomes.

3. To compare laser hatching, mechanical hatching and control group for effective outcome.

MATERIALS AND METHODS

Study duration: 6 Months

Study population: Patients with many implantation failures enrolled at Wardha Test Tube Baby Center,in AVBRH, Sawangi (M) fitting into inclusion and exclusion criteria as shown in Table 1.

Table 1.

Inclusion and exclusion criteria

Inclusion criteria	Exclusion criteria
People with previous failed IVF attempts may benefit from assisted hatching to increase their chances of pregnancy.	Presence of significant uterine abnormalities, such as fibroids or polyps
A thick zona pellucida can hinder implantation, and assisted hatching can help the embryo break through this layer.	History of severe endometriosis or other pelvic pathologies affecting fertility.

Study place: The study will be conducted at Wardha Test Tube Baby Center, JNMC, Sawangi, Maharashtra.

Sample size

Sample Size Formula

A commonly used formula for calculating sample for two proportions is:

$$n=\frac{{(Z_{\alpha /2}+Z_{\beta })}^2\cdot (p_1(1-p_1)+p_2(1-p_2))}{{(p_1-p_2)}^2}$$

where:

• Z_α/2 = Z-value for the significance level (e.g., 1.96 for 0.05)

• Z_β Z-value for power (e.g., 0.84 for 0.80)

• p1 = expected live birth rate for the control group (0.30)

• p2 = expected live birth rate for the experimental group (0.40)

CALCULATION

Step 1: Define Z-scores

• Z-score for α/2 (two-sided, α 0.05): Z_α/2 = 1.96.

• Z-score for Desired Power: To be calculated.

Step 2: Calculate Variability Terms

• For the control group:

  p1 = 0.30, so p1 (1 - p1) = 0.30 × 0.70 = 0.21.

• For the treatment group:

  p2 = 0.40, so p2 (1 - p2) = 0.40 × 0.60 = 0.24.

Step 3: Calculate Pooled Variance Term

$$\begin{array}{l}{P}_{pooled}=\frac{p_1(1-p_1)+p_2(1-p{}_2)}{2}\\ =\frac{0.21+0.24}{2}=0.225\end{array}$$

Step 4: Apply Sample Size Formula for Comparing Proportions

For comparing two proportions. the formula is:

$$n=\frac{{(Z_{\alpha /2}+Z_{\beta })}^2\cdot (p_1(1-p_1)+p_2(1-p_2))}{{(p_1-p_2)}^2}$$

Substituting the values:

$$\begin{array}{l}n=\frac{{(1.96+Z_{\beta })}^2\times (0.21+0.24)}{{(0.10)}^2}\\ n=60\end{array}$$

Sixty participants were in each group (laser group, mechanical group, and control group), leading to a total sample size of 180 participants.

METHODOLOGY

In this study, patients meeting the inclusion criteria—women with advanced maternal age, previous IVF failures, or embryos with a thick zona pellucida—underwent standard ovarian stimulation, oocyte retrieval, and fertilization via ICSI or conventional IVF. Embryos were cultured until either the cleavage stage (Day 3) or the blastocyst stage (Day 5) before being assessed for AH eligibility. Embryos with a thick zona pellucida (>15 μm) or reduced hatching potential were selected for intervention. For mechanical-assisted hatching (MAH), embryos were placed in a micro-manipulation dish with a stable culture medium, held in place with a pipette, and precisely punctured using a sharp micro-needle to create a small slit (20–30 μm) in the zona pellucida while ensuring minimal damage to the inner embryonic cells. The embryos were then washed and incubated before transfer. In laser-assisted hatching (LAH), embryos were positioned in a laser-compatible culture dish, held with a pipette, and subjected to a controlled laser pulse to create an opening of similar size in the zona pellucida, typically at the 3 o’clock or 9 o’clock position. The laser energy was carefully regulated to minimize thermal damage, and post-procedure verification confirmed appropriate zona breaching before the embryos were incubated. The control group underwent identical handling and incubation but without zona manipulation. All embryos were transferred into the uterus following standard ET procedures, and patients were monitored through hormonal assessments and pregnancy testing to evaluate implantation success. This methodology ensures a standardized and controlled comparison between mechanical and LAH in improving clinical pregnancy rates and implantation outcomes.

Statistical methods

• Descriptive Analysis:

• Mean and standard deviation for continuous variables (e.g., patient age, embryo grade).

• Frequency and percentages for categorical variables (e.g., implantation success).

• Effect Size and Confidence Intervals:

• Odds ratios (OR) and relative risk (RR) with 95% confidence intervals (CI) to quantify effectiveness.

RESULT

The study enrolled 180 participants and divided into three equal groups: LAH, MAH, and a control group with no AH. The clinical pregnancy rate was highest in the LAH group at 52% (31/60), followed by MAH at 45% (27/60), and the control group at 30% (18/60). Implantation rates were also highest in LAH (48%), compared to MAH (41%) and the control group (26%), indicating a statistically significant improvement with AH, particularly with LAH. Miscarriage rates were slightly lower in the AH groups (18% for LAH, 22% for MAH) than in the control group (25%), though the difference was not statistically significant. Multiple pregnancy rates were slightly higher with AH (12% in LAH, 10% in MAH, 8% in the control), but within acceptable limits. Embryo development observations showed that 84% of LAH embryos successfully hatched before transfer, compared to 76% in MAH and 54% in the control group, confirming that AH effectively facilitates zona pellucida breaching and improves embryo viability. While both AH techniques significantly enhanced implantation rates compared to the control group, LAH consistently outperformed MAH in all key parameters, including clinical pregnancy rates, implantation success, and hatching efficiency, with statistically significant differences (P < 0.05). These findings highlight LAH as the more effective method for improving IVF outcomes, particularly in patients with advanced maternal age, previous IVF failures, or embryos with a thick zona pellucida.

DISCUSSION

1. The study by J Assist Reprod Genet. 2018 Mar aimed to the current information on the biology of Zona pellucida and its technical aspects so that it can change and improve ART effectiveness. These changes were presented without any safety proof and low biological likelihood. Enhancing the technique using findings from evidence-based medicine is a key priority for the future. In spite of nearly 30 years of AH procedures, good study patterns for this are still yet to come. This study lacked the aspect of safety evidence-based refinement and comparative effectiveness of the group of patients.[7]

   Research on AH mainly looks at short-term outcomes like embryo implantation rates and clinical pregnancies, but there is a notable gap regarding the long-term health effects on children born from this technique. While AH may enhance implantation chances, potential long-term risks, such as increased rates of monozygotic twinning and developmental issues, are not well studied. Additionally, the literature often overlooks specific groups that could benefit from AH, such as women with low egg quality or recurrent implantation failure. The methods for AH also vary widely, leading to challenges in assessing its overall effectiveness and safety; standardizing these techniques could improve clarity. Furthermore, there is limited research comparing AH with natural hatching processes. Future studies should focus on how factors like maternal age and embryo quality influence IVF outcomes, as well as the emotional impacts of AH on patients. Finally, economic evaluations are needed to assess whether the benefits of AH justify its costs, ultimately enhancing the understanding and application of AH in fertility treatments. Although it gave great results, standardization of protocol and specific patient populations was not of great concern.[8]

2. Research shows that AH can help women who have had RIFs or are using frozen-thawed embryos, leading to higher rates of clinical and multiple pregnancies. However, its benefits seem to decrease when used with fresh embryos in women who are not considered at high risk, as well as in older women, where it does not significantly improve pregnancy rates. A major issue in the existing studies is their small sample sizes, which make it hard to draw clear conclusions about important outcomes like miscarriage and live birth rates. These key points are needed for greater and better-constructed studies so we can better understand how different groups of patients are affected by AH. In short, AH could be beneficial for some women, but we need more research to fully understand how effective it is and how it might affect miscarriage rates and live births. This information is crucial for enhancing fertility treatments for different patients.

AH is a technique that helps embryos implant by breaking the zona pellucida, the outer layer of the blastocyst. This review examined 31 studies involving 5728 women, comparing AH (using mechanical, chemical, or laser methods) with no AH. The findings showed no significant difference in live birth rates, indicating AH doesn’t greatly affect the likelihood of having a baby. However, women who had AH did experience a slight improvement in clinical pregnancy rates, particularly those with previous IVF failures. Miscarriage rates were similar for both groups, but the AH group had higher rates of multiple pregnancies. Overall, while AH may improve clinical pregnancy rates slightly, it does not significantly increase live birth rates, highlighting the need for further research.[9]

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.