3. Discussion
During the proliferation process, bacteria created endotoxin which is harmful to embryonic development [7]. Washing is a commonly used method to remove microorganisms from the embryo surface. However, it may not be the most effective approach, as demonstrated by the patient in our study who experienced failed pregnancies despite careful washing of the embryos during the second and third transfers. This could be attributed to the high bacterial load in the culture medium and the qualitative nature of the washing procedure leading to recontamination [4].
The zona pellucida is a critical structure that surrounds the oocyte and later the developing embryo in humans. The ultrastructure of zona pellucida has been clearly described in a related study [8]. It can act as a protective barrier to prevent multiple sperm from fertilizing the same oocyte. It also protects the developing embryo during its journey through the fallopian tubes towards the uterus. However, in our study, the zona pellucida can not protect embryo from bacteria. This can be explained due to the porous structure of the zona pellucida makes it challenging to completely eliminate microorganisms [5]. Indeed, Familiari et al. performed a scanning electron microscopy (SEM) to prove the spongy structure of zona pellucida of mature oocytes [9]. Additionally, during the clevage and blastocyst stage of embryo, the outer surface of the zona pellucida also showed a spongy texture with wide and flattened fenestrations. Therefore, we suggest that zona pellucida removal is an optimal method to stop bacteria contamination. This approach can be done sucessfully using both chemical (Tyrode acid) and physical method (Laser). However, the effectiveness of Tyrode acid can vary depending on the thickness the zona pellucida. Additionally, there is a slight risk of exposing the embryo to Tyrode acid, which could potentially affect its viability or development. In our study, by utilizing a laser to remove the contaminated zona pellucida from the embryos, the recontamination of bacteria was prevented, leading to a successful live birth for the patient. Moreover, the removal of the barrier between the embryo and the uterine environment potentially enhanced implantation and increased the chances of a successful pregnancy [10].
In this case, the use of laser for zona pellucida removal allowed for precise and controlled manipulation. It also can be used in a wide range of cases, including embryos with thick or tough zona pellucida. It is worth noting that the successful outcome obtained in this patient after repeated implantation failures, with a healthy live birth, suggests the potential benefit of this technique. However, further studies with larger sample sizes and controlled settings are needed to validate these findings. Additionally, it is important to consider the risks and limitations associated with zona pellucida removal. The procedure requires skilled personnel and specialized equipment to ensure proper execution and minimize the risk of damage to the embryo. There is a possibility of damage to the embryo during the removal process, potentially impacting its viability. Long-term follow-up studies are necessary to evaluate the potential effects of zona pellucida removal on fetal development and health.