Monday, May 27th

Last updateSun, 21 Feb 2021 9am

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Will all my eggs fertilize?

Usually not all the eggs (oocytes) from oocyte retrieval fertilize and depends on the quality of spermatozoa and on the quality of the oocytes.

However, first we have to understand fertilization:
Fertilization is the process by which the spermatozoa (containing half the genetic material) unites with oocyte (also carrying half the genetic material) resulting in the creation of a single cell (zygote) containing the sum total of chromosomes (a mixture of genetic characteristics from both parents).



1st day- the fertilized oocyte contains 2 nuclei (one with DNA from the father, the other from the mother)
These "pronuclei" are visible to the embryologist, 16-18 hours after fertilization. The fertilized oocyte (zygote) contains the essential 46 chromosomes to develop into the embryo.


After fertilization the vitalize oocyte begins its procedure to divide, first into 2 cells, then 4, 8 etc., etc.
We do not expect all the oocytes to fertilize and that depends not only on the ability of the spermatozoa to penetrate the oocyte, but also on the ability of the oocyte to accept the sperm.
The semen analysis is a test that can give us information about the spermatozoa but it not a definitive test that will tell us if the sperm has the ability to fertilize the oocyte. The number, morphology and motility of the sperm can guide us to a conclusion of the quality, and can give us an idea as to whether the method ICSI or "classical" IVF will be used on the day of oocyte retrieval. The most important parameter for fertilization success remains the oocyte quality.
The protocol that the woman follows for super-stimulation of the ovaries depends on many factors such as age and previous responses in IVF attempts in order to succeed in retrieving the most mature.

The oocyte retrieval is timed to produce the most mature oocytes, which is accomplished by a series of ultrasound scans during treatment. We estimate a mature follicle (containing a mature oocyte) has a diameter of ~17-18 mm .



Your cycle is monitored by ultrasound scans and blood tests (oestradiol).

On the basis of these tests we arrange your next visit and decide if a change in dose is required.
The aim is to achieve many follicles ~ 18mm, to estimate the maturity of the oocyte and to program the day of your oocyte retrieval.

The hormonal treatment stimulates the ovary to produce more than follicle. The follicles may be of varying sizes but with the final injection (HGC) we try to synchronize the development of the follicles to give us the most number of mature oocytes.
Ôhe more mature oocytes we can retrieved increases the chances of them fertilizing and subsequently having enough embryos to select the best ones for embryo transfer.
Of course, this does not mean the more oocytes the better chance you have of pregnancy, what is more important is to have fewer mature oocytes rather than many immature ones!


What is a "mature" oocyte?

A Mature oocyte is at the correct stage of development both chromosomally and cytoplasmically (the substance of the oocyte). It is surrounded by mature cumulus cells and has a mature protein coat (zona pellucida) to accept the spermatozoa.



The oocyte after retrieval. Cumulus cells surround the oocyte. One purpose of these cells is to prevent all the spermatozoa from arriving at the surface of the oocyte at the same time but they also they function as a sail to travel down the fallopian tubes to the uterus.




Immature oocyte. The Germinal Vesicle is visible to the embryologist. The structure contains 46 chromosomes and has not divided to half the genetic material to become "mature".
This stage cannot be fertilized and rarely matures in vitro..



Intermediate stage - immature stage without polar body
The oocyte at this stage can sometimes mature in vitro.




Mature oocyte with polar body. Now the cell contains half the number of chromosome. The surplus chromosomes are dispelled in the polar body (polar body situated at 12 o' clock).
Containing 23 chromosomes the oocyte is ready to be fertilized by the sperm-to supplement the number of chromosomes to the complete 46.