The embryologist takes about 4 to 6 eggs or more for the fertilisation process. Usually, most of these eggs fertilise. The number of eggs that fertilise will vary based on certain criteria such as egg quality. All the eggs may fertilise, or only some may fertilise. An embryologist can never be sure about the quality of the eggs and sperm, and hence they prefer to use a sufficient number of eggs to give them a few embryos.
The embryologist selects what they consider to be mature and healthy eggs. When an embryo does not fertilise, it could be a problem with the egg or the sperm or both. At times there are chromosomal abnormalities which prevent the fertilisation process from taking place. This will result in a defective embryo and a deformed baby if it is allowed to grow. This is nature’s way of conservation of the species by naturally eliminating the weak.
Under the blastocyst procedure, the eggs that fertilise are left to develop by themselves for 5 or 6 days. By the sixth day, the embryo has approximately 200 cells. This procedure allows the embryologist to study the embryos.
The Blastocyst procedure is commonly being practised for IVF treatment as it has a number of benefits attached to it. Many embryos arrest before Day 5. The blastocyst procedure has the benefit of eliminating this day 5 embryo arrest thus ensuring a higher embryo survival rate and increasing the IVF success percentage. The couple undergoing the treatment as well as the consulting doctor are keen that the IVF treatment leads to a successful pregnancy.
Embryos with chromosomal abnormalities either die or the abnormality becomes very apparent by the 5th day of the embryo development. Hence blastocyst also reduces the possibility of birth defects due to chromosomal abnormalities. Parents are always fearful of their child having birth defects and abnormalities. The Blastocyst procedure helps to reduce this to a considerable extent.
Blastocyst is preferred as a technique as it matches the natural pregnancy process more closely. Usually, an embryo remains in the fallopian tubes for 2-3 days before moving to the uterus. The embryo moves to the uterus approximately 80 hours after fertilisation. The uterus has been designed to take an embryo that is 4 days old. Therefore the Blastocyst technique is more suitable and has a better chance of embryo implantation success.
Implantation only begins about 5 to 7 days after fertilisation. With a blastocyst transfer, the embryo is ready for implantation. Sometimes a blastocyst begins to hatch in the lab itself before transfer to the uterus. An embryo has an outer covering which it sheds before it is able to attach itself to the uterine lining. There are occasions when the IVF procedure has failed due to the embryo not hatching and hence not being able to implant. This was a greater likelihood in the cleavage stage transfer, which is embryo transfer after 2 or 3 days after fertilisation.
When the embryo is ready to hatch, doctors can use a technology called assisted hatching, which helps the embryo to hatch and enables it to attach to the uterus wall. In some cases, even if the embryo does not begin to hatch after day 5. The assisted hatching procedure is used to improve the chances of success of the IVF procedure. Assisted hatching entails making a small hole in the outer embryo shell to enable it to break out and attach itself.