If you have already done some research about infertility treatments and in-vitro fertilization (IVF), then chances are high that you have already bumped into the complex-sounding word—blastocyst. Well, it is nothing but a 5-6 days old fertilized egg, or a mass of fast-dividing cells that is on its way to developing into an embryo. Sounds simple? It is.
But, before we get into complex topics such as blastocyst culture, let us look at what is a blastocyst, its relevance in facilitating pregnancy, blastocyst implantation, and its role in assisted reproductive technology (ART) procedures such as IVF.
Fertilization occurs when a mature egg unites with a sperm. In the natural course of action, this happens in the fallopian tube of the female partner. Then the fertilized egg rolls down the tube into the uterus and implants itself in the uterine lining. Here it develops into an embryo that later grows into a baby. It takes about 5-6 days for the fertilized egg to find its way to the uterus. Meanwhile, the cells continue to divide and form a mass of cells. By the time it reaches the uterus, it is ready to latch onto the uterine wall and hatch into an embryo that becomes a fetus.
Assisted reproductive technology (ART) based fertility treatments such as IVF and intracytoplasmic sperm injection (ICSI) are based on handling eggs and sperm outside the body, fertilizing the egg in a controlled lab setting, and transferring the fertilized egg to the female partner or surrogate’s uterus.
Many doctors prefer transferring fertilized egg when it is 3-4 days old so that it can develop into a blastocyst in the natural environment inside the uterus and implant into the uterine lining when ready. However, some doctors prefer allowing the fertilized egg to continue growing in the controlled environment until it reaches the blastocyst stage and is ready for blastocyst implantation. In such cases, the blastocyst must be transferred before it hatches from its protective shell. Once hatched, it is no more viable for transfer.
Blastocyst culture and implantation are ideally performed if the couple has a history of unsuccessful IVF cycles, or if the embryos obtained in the previous IVF cycles were of low quality. Quality control and optimal laboratory culture conditions are essential for successful blastocyst culture.
In an IVF process, following ovarian hyperstimulation and egg retrieval, the mature eggs are put into a fertilisation medium in the laboratory. There the eggs are either exposed to sperm or sperm is injected directly into the mature egg (ICSI) to facilitate fertilization. The medium contains essential nutrients to support the growth and development of the embryo. Thereafter, the fertilized eggs are placed in the embryo incubator for further growth and development.
By 5-7 days of fertilization, the egg reaches the blastocyst stage. In this stage, the egg contains enough cells to help the embryologist assess the quality of the embryos and grade them. The best blastocysts are chosen for transfer.
As the blastocyst implants, it releases HCG (Human Chorionic Gonadotrophin) hormone into the mother's bloodstream. The presence of HCG in blood confirms successful blastocyst implantation in the mother’s womb.
It is widely believed that if a fertilized egg can survive and thrive up to the blastocyst stage in an external environment, then it will be easier for it to implant and hatch in the natural environment—the uterus. Also, blastocyst culture helps in obtaining the best quality embryos that can assure more live births. Here are some advantages of blastocyst culture.
One of the biggest risks and disadvantages of blastocyst culture is that none of the fertilized eggs grows to become a blastocyst. If that happens, you may not have an embryo for blastocyst transfer. There could be several reasons for fertilized eggs not developing into blastocysts. The most common reasons are genetic issues in the embryo or intolerance to the artificial medium. In such situations, a three-day transfer may have helped the fertilized egg to grow in the natural environment. However, you miss the three-day embryo bus, if you wait for blastocyst transfer.
While blastocysts surely increase the chances of implantation, they cannot assure positive pregnancy. When a blastocyst is transferred to the uterus of the female partner, it secretes protein molecules as an early signal for implantation. During this time, the endometrium, popularly known as the uterine lining, must be receptive to allow the embryo to implant and grow. Is this a common question on your mind - do blastocyst always implant ?
Mostly blastocyst implantation failure happens because of the following two reasons:
And, there is not much you can do about either of the above reasons. What you can do to assist implantation includes eating a balanced diet, staying active to promote good blood circulation, exercising gently, and remaining relaxed and stress-free.
Now that you know all about blastocyst culture and transfer, discuss your options with your doctor and go ahead with the most viable one for you and your partner. Remember, blastocyst culture and transfer do not promise implantation, but they surely increase your chances of positive results.
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