What is the difference between embryo culture in vitro with and without blastocyst formation? Analysis by Chen Yilu from Tulip International Fertility Center

During the IVF treatment process at Tulip International Fertility Center, many patients will hear the term "blastocyst culture", but their understanding of the significance and risks of blastocyst culture is not comprehensive. Blastocyst culture and non-blastocyst culture are two different embryo culture strategies, each with its own advantages and applicable populations. The choice of which method to use needs to be determined based on the specific situation of the patient.

What is blastocyst culture and no blastocyst culture

"Non-blastocyst culture" refers to the traditional method of embryo culture, which involves culturing the fertilized egg until the third day, when the embryo develops to the cleavage stage with about 8 cells, and then transferring or cryopreserving it. This method is still widely used today.

Blastocyst culture involves continuing the cultivation of embryos from day 3 to day 5 or 6, allowing them to develop into blastocysts. The blastocyst stage represents a more advanced phase of embryonic development, where the inner cell mass and trophoblast cells have differentiated, and the number of cells has reached hundreds.

The main advantages of blastocyst culture

The primary advantage of blastocyst culture lies in its ability to facilitate natural selection. From day 3 to day 5, embryos undergo a critical period of rapid division and cellular differentiation. Embryos with poor developmental potential or chromosomal abnormalities often fail to successfully develop to the blastocyst stage and cease development during the culture process. Therefore, embryos that can form blastocysts are generally of better quality and possess stronger developmental potential.

Clinical data reveals that the implantation rate and clinical pregnancy rate of blastocyst transfer are generally higher than those of cleavage stage embryo transfer. This is because blastocysts are closer to the developmental stage that embryos reach the uterus in a natural state, are more synchronized with the development of the endometrium, and are therefore more likely to implant.

In addition, blastocyst culture is also beneficial for preimplantation genetic testing (PGT). Sampling from the trophoblast cells of the blastocyst for testing causes less damage to the embryo itself and results in higher detection accuracy.

The risks associated with cyst cultivation

Culturing blastocysts is not without risk. The primary risk is the possibility of having no blastocysts available. Not all embryos on day 3 can be successfully cultured into blastocysts, and the blastocyst formation rate is typically between 40% and 60%. If the patient's embryo quantity is limited and the quality is average, there may be no blastocysts after culture, resulting in no embryos available for transfer in the current cycle.

In contrast, if the option of not culturing to the blastocyst stage is chosen and transfer is performed on day 3, although the success rate of a single transfer may be lower, at least the opportunity for transfer is preserved. For patients with poor ovarian reserve function, few retrieved eggs, and poor embryo quality, not culturing to the blastocyst stage may be a safer choice.

How to choose between blastocyst culture and non-blastocyst culture

Whether to proceed with blastocyst culture requires a comprehensive assessment based on factors such as the patient's age, ovarian reserve, embryo quantity and quality, as well as previous transfer outcomes.

Patients under the age of 35 with good ovarian function and a relatively large number of embryos obtained (usually at least 5-6 high-quality embryos are recommended) are more suitable for blastocyst culture. After undergoing blastocyst culture, these patients still have a high probability of obtaining usable blastocysts, and the high success rate of blastocyst transfer can enable them to achieve pregnancy more quickly.

For patients who have repeatedly failed in transferring cleavage stage embryos, it is also recommended to try blastocyst culture. By performing natural selection through blastocyst culture and combining it with PGT technology to screen for chromosomal abnormalities, the causes of failure can be identified, thereby improving the success rate of subsequent transfers.

However, for patients who are of advanced age, have poor ovarian reserve, or have a small number of embryos, caution should be exercised when expanding the blastocyst. If there are only 2-3 embryos of average quality on day 3, expanding the blastocyst may result in the complete loss of embryos. In such cases, it may be a more reasonable choice to first transfer the embryos on day 3, giving oneself a chance to try.

Both cyst cultivation and non-cyst cultivation have their own advantages and disadvantages, and no single approach is inherently superior. The key is to develop a personalized plan based on individual circumstances and make choices that suit oneself under the professional advice of a doctor.

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