Fertilization
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).
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1st day- the fertilized oocyte contains 2 nuclei (one with DNA from the father, the other from the mother) |
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 .
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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.
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Intermediate stage - immature stage without polar body |
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