Frozen Blastocyst Transfer & Embryo Implantation

What is a blastocyst?

An embryo with a large, central, fluid-filled cavity and two distinct cell types is termed a blastocyst. Typically, embryos that can develop into blastocysts have by 5 or 6 days after the time of insemination.

The cells found in the middle of the blastocyst are known as the inner cell mass and will eventually form the fetus after implantation. The single layer of cells on the outside of the blastocyst forms the trophectoderm, which will form the placenta.

Blastocyst culture 

Until this time, it was difficult to culture embryos to the blastocyst stage of success. Science has taken steps forward to create culture media that imitate the shifting environment of the reproductive tract and comply with the embryo’s diverse needs as it travels up the fallopian tubes. In the laboratory, approximately 65% of embryos achieve successful growth to the blastocyst stage.

Stages of blastocyst development in blastocyst culture

These embryos are then placed in an incubator for further development, right after they undergo the IVF laboratory procedure of egg retrieval. In-vitro fertilization or intra-cytoplasmic sperm injection is used to fertilize the eggs after this process.

Developmental stages of an embryo

• Day 0: The day of egg retrieval
• Day 1: Pronuclear, checked by the embryologist of how many eggs have successfully fertilized
• Day 2: Two to four-cell
• Day 3: Eight-cell stage
• Day 4: Morula stage
• Day 5 or 6: Blastocyst stage.

Blastocyst culture procedure

The steps for blastocyst culture can be summarized in four broad steps, which include;

• Fertilization of eggs by sperm in either IVF or ICSI

This fertilization process in IVF is achieved through the mixing of eggs and sperm in a petri dish. It may further require ICSI, an ART method more precise than traditional IVF, as it injects a single identified and healthy sperm directly into the egg. This is usually done in conjunction with the process of egg retrieval.

• Culture in a specialized medium of resulting embryos

Fertilized eggs or embryos are placed in specialized culture media that provide all the necessities to nourish the embryo to grow. This is then followed by an incubator placement, where conditions are simulated to mimic those of the human body in order to support growth.

• Embryo observation and monitoring for growth to the blastocyst stage:

Embryologists monitor the growth of embryos to track their progress. They keep checking on the embryos under a microscope and are always ascertaining that they are developing at the expected rate in terms of quality. Some of the embryos may have formed into blastocysts on days 5 or 6.

• Selection and transferring of the healthiest blastocysts into the uterus

The best-quality blastocysts are selected for transfer into the uterus. This process therefore involves very gentle removal of the blastocysts from the culture medium, putting them into a thin catheter. The catheter is then introduced into the uterus, after which the blastocystes are released. The procedure is usually conducted under ultrasound and does not require anesthesia.

Role of blastocyst culture in IVF

Blastocyst culture is a crucial step in the IVF process. Blastocyst culture is beneficial for individuals who choose IVF for the act of conception. It is an important step in relation to the success rate of fertility treatments using IVF.

The advantages of the blastocyst culture stage over earlier embryonic development stages as part of the IVF process are as follows:

• Increase in probabilities for implantation: At this stage, the embryos have a larger chance of implantation compared to earlier stages; therefore, their chances of getting pregnant also increase.
• Reduced risk of multifetal births: The risk of multifetal births is reduced by the process of selecting the most viable and healthy blastocysts for transfer. This also reduces the risk of obstetric complications brought about by multifetal pregnancies.
• In fact, cryopreservation has a greater chance these days because now single embryo transfer is preferred, so more embryos can be frozen for later FET cycles in the case that one or more of them are to be transferred for successful pregnancies.

What are the advantages of blastocyst culture? 

One of the biggest challenges with an embryo’s appearance is that it is very difficult to predict any resulting blastocyst formation or its potential for implantation. If we have many embryos at a stage in development that is very early, it becomes particularly challenging to decide which embryos have the greatest chance to give rise to a healthy pregnancy.

Embryos may be noticeably different when transferred to the laboratory on day 5 because they start to form into blastocysts. This can mean that, when there are several embryos to choose from, the team carrying out the embryology would be able to pick the most suitable ones for transfer.

Transferable implantation potential is as high as 60% per blastocyst. It is important that the single best-quality blastocyst be transferred in the hope that the transfer will result in a healthy singleton pregnancy and a reduction in multiple pregnancies with their associated risks.

Also Read : भारत में IVF का खर्चा

Why is blastocyst culture so successful? 

Blastocyst transfer naturally mirrors the process of conception, where the embryo travels down the fallopian tube to finally settle in the uterine cavity five days after fertilization. This then influences the development of the embryo as well as the lining of the womb to increase chances for implantation.

Selection pressure on a group of embryos will be exercised through blastocyst culture, whereby only the strongest and the fittest will develop a successful pattern towards developing to the blastocyst stage. This means selectively transferring the embryo after excluding slow and arrested blastocyst culture will increase the chance of transferring a normal embryo with high implantation potential and, ultimately, achieving a successful pregnancy.