INTRACYTOPLASMIC SPERM INJECTION (ICSI) AND EMBRYO FOLLOW-UP
On the ovum pickup day, the cells around the collected oocytes are removed and the maturation of the oocytes is checked. Approximately 80% of the oocytes collected are defined as mature under normal conditions. We can only take mature (M2) oocytes to the ICSI process.
ICSI process is applied to all mature oocytes on the same day under a special microscope. The method involves injection of 1 sperm belonging to the spouse into each oocyte with a special technique, and then storing the oocytes in special devices called incubators. The day after the ICSI procedure (approximately 17 hours), all oocytes are evaluated for their fertilization status. Under normal circumstances, we would expect approximately 75-80% of oocytes that ICSI is applied to be fertilized.
Then, the embryos placed in special medium are continued to be followed in the devices we call incubators, in an environment that mimics the oxygen, humidity and temperature of the female body. After fertilization, the cells of the embryos divide into two every 12-14 hours, so that the embryo reaches 8-cell development stage 72 hours after oocyte pickup. The development of embryos until the 4th day is called the cleavage stage, and the development from the 5th day is called the blastocyst stage. The embryo, which has reached the blastocyst stage, now possess 250-300 cells. Thus, the number of cells is no longer mentioned as in the cleavage stage, however, embryos are classified from 1 to 5-6 stages.
In order to determine the embryo quality, they are evaluated according to the division dynamics until the cleavage stage, the diameter difference between the cells, and the dead part ratios in the embryo volume. As a rule, in our clinic, we decide to follow until the blastocyst stage for the embryos of our patients who have 1 more good quality embryo than the number of embryos entitled to be transferred. Since every embryo cannot continue its development from the cleavage stage to the blastocyst stage, we can achieve higher pregnancy rates with embryo transplantation that has a continuous development and has turned into a good quality blastocyst. This allows us to more accurately select the embryo that will be more likely to implant to the uterus. However, it is vital to have laboratory conditions and incubators with appropriate temperature, humidity and gas ratios so that embryos can be safely kept in the laboratory environment until the blastocyst stage. We know very well that in the presence of embryos that cannot reach the blastocyst stage in the presence of good laboratory conditions, they will not complete their development in the uterus.
These evaluations require the embryos to be taken out of the incubator once a day and briefly examined under the microscope. However, in time lapse incubators, once the embryos are placed in the incubator, they can be evaluated by examining the images taken inside the incubator on the computer screen, without ever being taken out. For detailed information on this subject, you can read my article “Continuous Embryo Monitoring-Embryoscope”.