A blastocyst is the second and most important stage of the embryo and fetal development. A fertilized egg could take from 5 to 14 days to develop into a blastocyst. The blastocyst has more differentiated cells (about 50-150 cells) compared to normal embryos (6-8 cells). It has a very thin outer lining and it can easily be embedded into the uterine lining under suitable conditions.
What is a blastocyst?
It is a hollow cellular mass having a cluster of cells (ICM) within a cavity (Blastocoel) filled with fluids, the outer shell of the blastocyst is known as trophoblast (TE) which is very thin, and this layer is responsible for combining with endometrium to form fetal membrane and placenta.
Blastocyst and Embryonic Development
During ovulation, an egg travels from the ovaries to the uterus through the fallopian tube and gets fertilized by a sperm, and starts to develop into a zygote or ococyte. Inside the uterus, the fertilized egg forms a zygote which keeps on differentiating from 2-cell, 4-cell, 8-cell, and 16-cell to finally blastocyst stage. This process is known as blastulation and takes 5-14 days after fertilization. The blastocyst will hatch from the trophoblast and implant itself on the uterine lining as blastula – This process is triggered by hormones and is known as hatching. Only a well-developed blastocyst will be able to implant itself on the endometrium wall for embryonic development by gastrulation.
It could take several days for the hatching and implantation of the blastocyst. After implantation blastocyst develops into a placenta which provides oxygen, nutrients, and growth factors from the mother to the growing embryo. This embryo will differentiate into three types of tissue by the process of gastrulation and grow into a fetus. This could take 4 or more weeks. At this time pregnancy can be detected.
Note: The blastocyst formation takes 5-14 days after Fertilization and Embryonic Development takes 2-11 weeks after Fertilization.
Blastocyst Transfer for IVF Treatment
When an Infertile woman opts for an IVF treatment, the eggs are collected from the woman’s ovaries during ovulation by follicular aspiration. The eggs get fertilized in vitro by the sperm (collected from the male partner or donor sperm). The fertilized eggs are kept in culture under surveillance for embryo(s) development. The embryo(s) start to develop within 2-3 days which can be transferred back to the uterus for implantation – between 9-21 days of the menstrual cycle.
However, these 2-3 days developed embryos only have 6-8 cells which makes them weak, so they might fail to implant and establish a pregnancy. 60% of day 2-3 embryos aren’t effective and might possess chromosomal deformations. To prevent that, IVF facilities use extended blastocyst culture as an alternative treatment as a modified IVF treatment.
Extended Blastocyst culture
In extended blastocyst culture, the embryos are developed in culture for 5-6 days up to the blastocyst stage (having 50-150 cells). These more differentiated embryos possess a higher chance of implantation (50-60%) upon embryo transfer. Only a few fertilized eggs will be able to survive up to blastocyst and they might stop developing after day 4 or 5. The embryos on day 5 have the best potential for implantation. The blastocyst transfer has a higher chance of pregnancy of 50-60% in an IVF treatment.
The blastocyst usually takes 1 or 2 days to embed on the endometrium wall. And after 11-12 days of fertilization, it will completely implant on the endometrium and start to grow into the placenta.
Note: The extended blastocyst culture process doesn’t increase the quality of embryos but rather it increases the chances of choosing quality embryos for IVF.
Why is Blastocyst Transfer preferable?
Blastocyst transfer is preferred for an IVF treatment because it has a higher potential for a successful pregnancy. As a fully developed, a ready-to-hatch blastocyst is transferred to the uterus the endometrium accepts it easily for implantation. Also if only one quality embryo (blastocyst) is transferred then it lowers the chances of multiple pregnancies.
Here are some conditions where Blastocyst transfer is required:
- When there is recurrent IVF or Implantation failure
- To prevent embryo arrest
- To prevent multiple pregnancies
- Increase live birth rates
- 5-6 days embryo(s) shows optimal timing for implantation than 2-3 days embryo(s)
- A previous case of miscarriage
- When there is a uterine or endometrial issue
The additional PGT (preimplantation genetic testing) can help to choose the best blastocyst for Implantation. This way there won’t be a need for multiple embryo transfers leading to multiple births. Also, other blastocysts can be frozen for future needs.
Blastocyst transfers are known to have higher live birth rates. It also decreases the chances of embryo arrest, genetic disorders in the fetus, and miscarriage. If embryo arrest happens then it can be identified for probable problems.
Assisted Hatching, if required in case of uterine and other problems, can help with successful implantation.
Complications of Blastocyst Transfer
Although blastocyst transfer has low-risk factors compared to standard embryo transfer, the chances are still there. Blastocysts with chromosomal abnormalities may suffer embryo arrest. Or if it will be able to implant but later result in an early miscarriage. More than half of early miscarriages are the result of chromosomal abnormalities which can be minimized by testing blastocysts by PGS before transfer.
The babies born from blastocyst transfer have a risk of chromosomal disorders such as down syndrome and Klinefelter syndrome. But the case is similar to standard IVF treatment.
In rare cases (only 10%), when sperm quality is very poor, no embryo makes it to the blastocyst stage.
Also, blastocysts can’t be cultured for more than 5-6 days, after that they stop developing. Which can be used in a frozen embryo transfer in the future. So, freeze your healthy embryos just in case.
Other than that blastocyst transfer is similar to standard embryo transfer for IVF.
However, blastocyst transfer shows more positive results compared to normal embryo transfer. Furthermore, your doctor will clear all your doubts regarding the treatment.
Who is eligible for Blastocyst transfer?
Couples who have a case of recurrent IVF or IVF/ICSI failure. Blastocyst culture can be used for different factors depending upon patients’ needs and medical history.
Blastocyst Transfer at Risaa IVF
Risaa IVF, Delhi is famous for IVF treatment with successful blastocyst transfer. We prioritize the success of IVF and minimize the risk of multiple pregnancies with blastocyst transfer. Our embryologists choose the best embryo by culturing them in an ideal environment for 5-6 days up to the blastocyst stage and testing with PGS for any chromosomal deformations. Only quality embryos will be used for your IVF treatment for favorable implantation.