Blastocyst culture is a technique in which an embryo is developed in the laboratory for 4-6 days after fertilization before being placed in womb. The advantage of blastocyst culture is the improved efficiency of embryo selection, because it is more likely that the embryos with the best development capacity reach the blastocyst stage. There is a natural selection & a higher probability of pregnancy when using a blastocyst than with an embryo in the cell division stage proving ‘ survival of the fittest.’ The advantages of extended culture and blastocyst transfer are numerous. Blastocyst culture & transfer programme can only successfully run on the strong laboratory back up as it actually involves simulating the ‘in vivo” environment for extended period proficiently.
Embryologists with huge clinical experience, use of latest equipments & culture media and maintenance of high laboratory standards with strict quality control of laboratory environment, empowers us, at Anmol Fertility & IVF Centre to provide you with this advanced form of treatment successfully.
Historically embryo transfer following IVF or ICSI took place two or three days after egg collection when the embryo contains around six to eight cells. However, laboratory advances have meant that we can now culture embryos for five or six days. By this stage, the embryos have numerous cells (approximately 80 – 100) and start to form two distinct layers. The embryos are then known as blastocysts.
This extended culture till day 5 or 6 post fertilization is called as Blastocyst culture. Until recently, successfully culturing embryos to the blastocyst stage was difficult. Initially, only 17% of embryos reached the blastocyst stage and pregnancy rates using blastocysts were only 10%. Scientific advances have led to the development of culture media that mimic the changing environment of the reproductive tract and meet the unique requirements of the embryo as it travels through the fallopian tubes. This now allows up to 60% of embryos to successfully grow to the blastocyst stage in the laboratory environment.
Studies suggest that pregnancy rates improve if the embryos are left to develop to their blastocyst stage.
Familiarizing with the term ‘Blastocyst’
A blastocyst is an embryo that has been developed in the laboratory for five days after insemination. Blastocysts have a large, central, fluid-filled cavity and two distinct cell types.The growing embryo’s cell types first start to differentiate at the blastocyst stage. . The outer cells are flat, in single layer and tightly packed and surround the liquid-filled cavity of the blastocyst. The embryo attaches itself to the womb with the help of the outer cells, which form the placenta and the outermost embryonic membrane. The cells in the centre of the blastocyst fluid cavity spreading preferentially towards one pole, layered on top , by the outer cells, are called the inner cell mass and will give rise to the foetus following implantation.
Find out how it could help you.
- In a natural cycle, an embryo develops into the blastocyst stage as it is leaving the fallopian tubes and entering the uterus. An embryo needs to have reached blastocyst stage once it arrives in the uterus, to ensure proper implantation. Blastocyst culture exerts a selection pressure on a group of embryos and only the strongest and fittest will develop successfully to the blastocyst stage.. Culturing embryos to day five or six gives the embryos more opportunity to prove their developmental potential. Some fertilized eggs may even arrest (stop developing) prior to day 5. By selectively excluding slow and arrested embryos from transfer, blastocyst culture will increase the probability of transferring a genetically normal embryo with a high implantation potential. This will increase your chance of achieving a successful pregnancy. This ‘natural selection’ also enables the embryologist to more accurately choose the best embryo for transfer which offers the most likely chance of pregnancy
- Blastocyst transfer mimics natural conception in which the embryo travels down the fallopian tube and reaches the uterine cavity five days after fertilization. This exactly synchronizes the development of the embryo and the lining of the womb to increase the chance of implantation. This is certainly more physiological approach.
- With blastocyst implantation, unlike a day three embryo which must continue to develop following embryo transfer, a transferred blastocyst will implant much more quickly. Scientific evidence shows that blastocyst transfer success rates are higher than the transfer of day three embryos. Blastocysts have an implantation potential of up to 60% per blastocyst, thus improves efficiency of the transfer
- Blastocyst cultures are particularly useful when there is a good yield of more than 10 eggs.
- Blastocysts are also used with excellent results in embryo diagnosis. They are the best to be used for PGD/PGS.
- The ability to transfer a single blastocyst with a high implantation rate as opposed to two day 2 or day 3 embryos helps to increase your chance of a healthy singleton pregnancy and reduce the incidence of multiple births and the associated risks.
- Elective Single embryo transfer (eSET) is possible because of better embryo selection, This means that there are often additional blastocysts remaining after embryo transfer
- Extended culture and blastocyst transfer is a technique used after your eggs have been fertilized, which helps us to identify which of your embryos are most suitable for transfer. In some cases, it can help improve your chances of successful pregnancy. It is a useful technique if you’ve produced good quality embryos in a previous treatment cycle, but not achieved a pregnancy like recurrent IVF failures.
- If the blastocysts are of good quality they can be stored for use in a frozen embryo replacement cycle (FET) at a later date. The freezing process is known as vitrification. Currently,scientific reports indicate that the chances of pregnancy using blastocysts that have been vitrified is almost equal to those used in a fresh embryo transfer cycle.
Grading & selection of the best blastocyst
When assessing the quality of the blastocysts and selecting them for embryo transfer and freezing, both the cell count and the structure of the outer cells and the inner cell mass are examined with a microscope. When many cell types are observed, the blastocyst is given the letters AA, a lesser cell count is represented with the letter B and a low cell count with the letter C. As well as cell types, the blastocyst’s development speed is assessed. A small fluid cavity is visible in an early blastocyst (Development Stage 1), but the cell type count is difficult to estimate. At the actual blastocyst stage, the fluid cavity may be almost perfect (50-80%, Development Stage 2), perfect (more than 80%, Development Stage 3), or expanding (Development Stage 4). In an expanding blastocyst, the embryo grows larger as the cavity is filled with liquid and the shell (zona pellucida) becomes thinner. As the expansion proceeds, some of the embryo’s outer cells penetrate outside the embryo’s shell (Development Stage 5) and eventually the embryo hatches completely (Development Stage 6).
Scoring of blastocysts is an imperfect science, and some very nice-looking blastocysts do not necessarily produce a pregnancy. However, the basic rule of thumb is that the best embryos make it to the blastocyst stage, and therefore has a greater chance statistically of producing an ongoing pregnancy than a lesser quality one.
Can everyone have a blastocyst transfer?
The developmental stage and quality of the embryos are assessed by our expert embryologists and the doctors will guide and discuss with you the best day for your embryos to be transferred. The approach never supports ‘ One size fits all’. It has to be an individualized treatment decision and unbiased.
- Blastocyst transfer is not suitable for everyone. It is ultimately a laboratory selection process to identify the best embryo.
- In patients with only 1 or 2 embryos the embryos have already selected themselves for transfer and there is no significant advantage to leaving them outside of the uterus for longer.
- Not all embryos are happy and growing in the laboratory environment and for this reason you may benefit from a transfer on day 2 or 3. If your embryos are developing a little bit slow or they are not quite good enough quality the embryology team will recommend a day 2 or day 3 transfer. It is important not to feel disheartened as there is still a good chance of a successful pregnancy following a transfer on day 2 or 3.
- On average 40-60% of fertilized eggs reach the blastocyst stage. With low egg counts it poses the risk that no embryo can be transferred if the development of the embryo stops before it reaches the blastocyst stage. So considering the potential loss of the number of embryos, it is suitable if more than 10 eggs are obtained in a cycle.
Points to remember while attempting blastocyst transfer
The greatest disadvantage is that there is a 2% chance that none of the embryos will continue to develop and form blastocysts by day 5. This is because not every embryo has the capability of forming a blastocyst. It’s also fair to say that if an embryo cannot make it to blastocyst stage outside of the uterus, it’s highly unlikely that it would have done so if transferred on day 2 or 3.
Blastocyst cultures require optimal laboratory conditions, a culture solution that best supports the development of blastocysts and a low-oxygen culture environment.
It’s important to bear in mind that not all embryos will continue to develop into a blastocyst by undergoing extended culture. This can mean you have fewer suitable for transfer, or freezing for future use. This is why we are cautious about identifying patients who will benefit from blastocyst culture.
Blastocyst Transfer Procedure
Instead of transferring your embryos around two to three days after fertilization, when they reach the ‘four to eight-cell’ stage, we allow the embryos to develop for longer in our laboratory. This is extended culture, as the embryos develop for five to six days after fertilization before they are transferred. Fresh embryo transfer is performed in this type of culture 4-5 days after egg collection, instead of the traditional 2-3 days. Blastocystscan also be frozen when they are four, five or six days old. Fresh embryo transfer and frozen embryo transfer are both reliable methods.
The final stage of the process is the transfer of the embryo to the womb. A catheter holding the embryo is gently inserted into the cervical channel and into the uterine cavity guided by ultrasound. The catheter is then removed and checked to make sure the embryo has been transferred. After the transfer, you can return to normal with the embryo quite safe within the uterus. Following a blastocyst embryo transfer, a pregnancy test is usually arranged twelve days later.
What happens if I don’t have embryos suitable for this? Can I still use them for pregnancy?
Yes. If you don’t have four good quality eight-cell embryos on day three after fertlisation, although we wouldn’t suggest extended culture, the chance of pregnancy is still good using your embryos.
It’s important to remember that transferring an embryo two to three days after fertilization is still the standard, routine option for many IVF patients.
What if I have more than one blastocyst available for transfer? What are my options?
If you have more than one good quality blastocyst, we advise on the option of single blastocyst transfer, which helps to reduce the risk of multiple birth. As with normal embryo transfer, any remaining blastocysts you have can be frozen and stored for future use.