In the IVF process, sperm and eggs are fertilized to develop an embryo. Using a mixture of amino acids, it is placed in a special incubator. The condition inside the incubator is perfect for the growth and development of an embryo. One day after egg retrieval (the first day of fetal development), the embryologists start the evaluation of fertilization and separate the normally fertilized egg. On the second day of embryonic development, the normally divided fetus should have 2 – 4 cells and on the third day it should have 6 – 8 cells, this stage is called the cleavage stage. On the third day of fetal development, embryologists assess embryo and grade them based on several factors. The factors for grading the fetus are as follows: Under the microscope, the outer layer of the embryo should be uniformly smooth. Each cell should be approximately the same size The outer layer of embryo i.e. zona pellucida should be clear and it should not be very thick. Embryos in which the are of better quality and also cell division takes place normally, have a greater possibility of implantation. Therefore, embryos which are of good quality and in which cell division is taking place normally are chosen for implanting. The embryos which are being transferred depends upon the number of embryos to be transferred, quality of fetus, maternal age and days of transfer (third day vs. the fifth day) Third day vs Fifth day After egg retrieval, fertilization and early embryo cell division, on the third day of embryonic development, the fetus is transferred into the uterus. However, due to availability in scientific progress and advanced cultural media, embryo blastocyst stage (fifth or sixth day of development of embryo with 80 – 100 cells) can be developed in a lab. The ability to progress to the blastocyst stage of a fetus comes from the development of advanced cells within the embryo. After five days of growth, the cells of a normal healthy fetus divide several times and adapt to their tasks. An embryo that survives and grows in this stage of development is called blastocysts. The living embryo in this stage is strong and healthy, which is more likely to be implanted. In this way, it is better for an embryologist to choose one or two blastocysts rather than selecting many embryos, which reduces the likelihood of more than one pregnancy. However, not all eggs are able to fertilize and reach the embryo stage. It is because the eggs are unable to mature properly or the sperm is not able to fertilize the egg. In such a situation, doctors may recommend the following procedures for embryo transfer: Assisted hatching Approximately five to six days after fertilization, an embryo hatches through its outer membrane (zona pellucida) which would allow it to be implanted into the lining of the uterus. If you are an older woman or if many of your IVF attempts have failed then your doctor will recommend you Assisted hatching. Assisted zona hatching is an artificial In Vitro conception technique. Under this technique, for embryo hatching and implantation, a hole in the zona pellucida is made just before the embryo transfer is done. Frozen egg and embryo may cause zona pellucida to harden in this state-assisted hatching techniques are effective. Preimplantation genetic testing Until embryos reach a certain stage, it is placed in an incubator for development. A small sample can be extracted after five to six days of development. And then this sample can be tested for the exact number of genetic diseases or chromosomes. Embryos that do not have affected genes or chromosomes can be transferred to the uterus. Preimplantation genetic testing determines that the parent’s genetic problem will affect the infant or not, its potential can be reduced, while it can not eliminate the risk. In this situation, prenatal testing may be recommended.