Table of contents
One of the most important stages of the IVF program is obtaining mature, high-quality eggs suitable for fertilization. Normally, 75-90% of mature eggs should be present during follicle puncture. They are suitable for further fertilization. Immature oocytes cannot be fertilized because an important genetic process has not taken place in them – the separation of chromosomes and the readiness to unite with the chromosomes of the sperm. If the percentage of received immature oocytes is more than 10-25%, this creates a significant impact on the effectiveness of the IVF program.
What is oocyte maturity?
The process of egg formation and maturation is very complex and significantly different from the maturation of male germ cells. A girl’s egg supply is formed in utero during embryonic development and is then used up from the moment of birth. From embryonic formation to ovulation, each egg cell contains 46 chromosomes. Egg cells in the ovary are in an immature state and mature from the period of formation of the dominant follicle and the moment of ovulation. At the time of ovulation, the ovum enters the phase of metaphase II of meiosis and is completely ready (that is, it contains 23 chromosomes) to combine its genetic material with the genetic material of the sperm. This ensures the formation of the correct set of chromosomes in the future child. When stimulating the growth of follicles in IVF programs, our goal is to obtain eggs for their further preservation or fertilization. In the process of stimulation, we focus on the natural days of ovulation, therefore, in the active reproductive age, ovulation occurs on the 14-15th day of the menstrual cycle – it is on these days that the oocytes have time to properly mature and prepare for fertilization.
The probability of correct transfer of chromosomal material and conception is the highest. It is also important that the diameter of a follicle potentially containing a mature egg is 18-22 mm on average. Therefore, follicle puncture to obtain oocytes is usually performed on the 14th-15th day of the menstrual cycle, when most follicles have a diameter of 18-20-22 mm. Embryologists assess the maturity and quality of oocytes 2-4 hours after puncture.
If there are immature oocytes, then all conditions are created for their maturation in vitro. This technique allows obtaining maturation of oocytes in the conditions of the embryological laboratory outside the ovaries. But the rates of obtaining euploid (chromosomally healthy) embryos from the fertilization of such oocytes are much lower than from the fertilization of immediately mature oocytes at the M II stage.
What are the reasons for obtaining immature oocytes during follicle puncture?
The reason for obtaining immature oocytes during puncture is an insufficient surge of LH (luteinizing hormone), which ensures the maturation of oocytes. It should be noted that the correct reaction to LH occurs only with the appropriate size of the follicles. Today, there are also known genetic disorders, known genes in the receptor for LH or FSH, which ensure the growth of follicles and the formation of the correct reaction to LH. The response to LH may also depend on the reproductive age and on the woman’s intake of certain drugs that disrupt this sensitivity.
What happens if immature eggs are fertilized?
Immature oocytes cannot be fertilized, as normally an egg and a sperm must transmit 23 chromosomes each. Only under such conditions is the correct set of chromosomes formed in the future child. If the oocyte is immature, this is a sign that it did not have time to shed the extra 23 chromosomes and carries all 46 from the mother’s body.
What to do when receiving immature oocytes in a previous IVF program?
First of all, the reproductive doctor must find out the reason for obtaining immature oocytes in the previous cycle.
To analyze the diameter of the follicles, the time of introduction of the ovulation trigger (a preparation for the final maturation of oocytes), the diameter of the main follicles on the day of the trigger. Also, in this case, a genetic analysis is performed to understand the cause and select drugs for further stimulation, determine the number of days of stimulation.
The selection of an ovulation trigger or the use of a double trigger is carried out, which improves the process of oocyte maturation. The time between the introduction of the trigger and the collection of oocytes is determined. This requires the mandatory expertise and experience of a reproductive doctor and allows you to get the result – the birth of healthy children!