What is a Blastocyst?
The first thing we need to understand is what a blastocyst really is. Well, a blastocyst is an embryonic structure of dividing cells made by a fertilised egg. It’s an early stage of the embryo which is one of the steps that lead to pregnancy. A blastocyst generally forms from about five to six days after the sperm fertilises an egg. A blastocyst consists of mainly two cell types, that is, the trophoblast, which develops into placenta, and the inner cell mass which contains the stem cells of the embryo and that gives rise to all the cells and tissues in the adult organism.
Generally three days after fertilisation, an embryo contains about 6 to 10 cells. After the fifth or sixth day, the fertilised egg, that is, the blastocyst forms like a rapidly dividing ball of cells. The inner group of it becomes the more developed embryo, while the outer group of cells becomes the ones that nourish and protect the embryo.
The Structure of a Blastocyst
The structure of a blastocyst is made up of the overall three following components.
1.Trophectoderm:
It is the outer layer of the blastocyst, and it forms the trophoblast which is a key cell of placenta. It forms the extraembryonic tissues.
2.Inner cell mass:
It is the inner layer of the blastocyst and forms the entire embryo. It is the source of all embryonic stem cells that can form all cell types in the embryo. It forms fetal and extraembryonic tissues.
3.Blastocoel:
It is a fluid-filled cavity within the blastocyst and it contains high concentrations of lactate and some amino acids. It contains lower concentrations of glucose and pyruvate.
Stages of Blastocyst Development
There are four stages of blastocyst development.
- Zygote: A sperm and egg join to form a zygote.
- Blastocyst: The zygote travels to the uterus and divides into a blastocyst.
- Implantation: The blastocyst attaches to the uterine lining, usually near the top.
- Embryo: The blastocyst then develops into an embryo.
What is Blastocyst Transfer?
A blastocyst transfer is a procedure that involves transferring a blastocyst embryo into the uterus of the person. A point to note is that a blastocyst is a highly developed embryo that’s ready to implant in the uterine lining.
The blastocyst transfers are a type of in vitro fertilisation (IVF). In this case, the embryo is cultured in a laboratory until it reaches the blastocyst stage which is five to six days after the fertilisation. The blastocyst is then transferred to the uterus and it attaches to the uterine lining in a process implantation. Blastocyst transfers increase the chances of pregnancy and it may also reduce the risk of multiple pregnancies.
The Process of Blastocyst Implantation
Blastocyst implantation is the process where a fertilised egg, that is, a blastocyst attaches itself to the lining of the uterus, which is called “burrowing” into the uterine wall to begin the development as an embryo. This process involves the following stages.
1. Apposition:
The blastocyst at first comes into contact with the uterine lining, adhering lightly to the surface.
2. Adhesion:
The trophoblast cells of the blastocyst firmly attach to the endometrium, facilitated by specific adhesion molecules.
3. Invasion:
The trophoblast cells actively penetrate deeper into the uterine lining, creating a space for the developing embryo to embed.
Blastocyst Cryopreservation: Procedure and Benefits
How are Blastocysts Frozen?
Blastocysts become frozen (Cryopreservation) using a rapid freezing process called vitrification. This process involves using cryoprotectants to protect the embryos from damage caused by ice crystals.
Steps of Vitrification
- Embryos are placed in a solution containing cryoprotectants.
- The embryos are then dipped in high concentrations of cryoprotectants for a few minutes.
- The embryos are rapidly cooled to an ultra-low temperature.
- The embryos are then stored in tanks of liquid nitrogen.
Benefits of Vitrification
Vitrification minimizes the risk of cellular damage, which increases the survival rate of embryos when they are restored to the normal body temperature. This can lead to improved outcomes in subsequent IVF cycles. Frozen embryos can improve the success rate of clinical transfers, chemical pregnancies, live births and reduce the risk of pregnancy loss. Frozen embryos can be stored for an unlimited time.
Success Rates of Frozen Blastocyst Transfers
Factors Influencing Success Rates
Factors that influence the success rate of frozen blastocyst transfers are female age, embryo quality, endometrial thickness, the method of endometrial preparation, the number of embryos transferred, the blastocyst quality, the transfer procedure, and the duration of the embryo storage.
Points to note about these factors:
- Age: Younger women generally have higher success rates due to better egg quality.
- Embryo quality: The morphology and developmental stage of the blastocyst impacts the implantation potential in a significant way.
- Endometrial thickness: A well-prepared endometrial with an appropriate thickness is crucial for successful implantation.
- Endometrial preparation method: Different protocols like natural cycles and hormone replacement therapy can affect the outcomes.
- Number of embryos transferred: Transfer of multiple embryos can increase the chance of pregnancy, but also raises the risks of multiple pregnancies.
Fresh VS Frozen Blastocyst Transfer Outcomes
Frozen blastocyst transfers sometimes have better outcomes than fresh blastocyst transfers in terms of live birth and birth weight. However, some studies don’t find a significant difference between the two in case of outcomes.
Some studies also say that fresh blastocyst transfers have an increased risk of preterm birth, and that pregnancies from frozen blastocyst transfers are less likely to be ectopic.
Potential Risks and Considerations
The following are the potential risks of blastocyst transfers:
1. Preterm birth:
Pregnancies after blastocyst transfer have a higher risk of preterm birth than those after cleavage stage embryo transfers.
2. Large-for-gestational-age babies:
Blastocyst transfer is associated with a higher risk of large-for-gestational-age babies.
3. Gestational diabetes:
Blastocyst transfers increase the risk of developing gestational diabetes.
4. Congenital anomalies:
There are some concerns that the blastocyst transfer increases the risk of congenital anomalies.
5. Epigenetic modifications:
There are concerns that blastocyst transfers increase the risk of epigenetic modifications.
Conclusion
Blastocyst transfers and cryopreservations has their own advantages and disadvantages. So, it depends upon what is suitable for different individuals after consulting with their certified doctors.
FAQ’s
1. Is blastocyst transfer right for me?
Blastocyst transfers has their own benefits and risks. Consult your doctor before making a decision.
2. Which is better? Frozen or fresh blastocyst transfer?
In some cases, frozen blastocyst transfers have better outcomes than fresh blastocyst transfers. But there isn’t a definite answer. You should consult your doctor in order to understand which is the right method for you.
3. What are the risks in blastocyst transfers?
The main potential risks of blastocyst transfers are preterm birth, large-for-gestational-age babies, gestational diabetes, congenital anomalies and epigenetic modifications. You need to consult your doctor before making any decision about whether to go for a blastocyst transfer.