Friday, Jun 14th

Last updateSun, 21 Feb 2021 9am

Font Size



G Nikas2

Fertilisation Check






The fertilized oocyte has 2 pro-nuclei (one containing the chromosomes from the male –carried by the sperm, and the other containing the chromosomes of the mother).

The pro-nuclei are visible to the embryologist 18 hrs after fertilization.

These are separated from the unfertilized oocytes and cultured until the day of embryo transfer.




Only one pro-nuclei has been activated.

These are separated from the fertilized oocytes and are not considered suitable for transfer.




Three or more pro-nuclei are caused by more than one sperm entering the oocyte or a error in egg cell division.
 These are separated from the fertilized oocytes and are not considered suitable for transfer.



From fertilization to the transfer.
During the oocyte retrieval the oocytes are visualized by the embryologist, collected and placed in culture medium specially designed to give nutrients to the developing egg (oocyte) and embryo.
The oocyte, spermatozoa and embryo are placed in incubators to maintain the ideal conditions for their growth in vitro. The correct temperature and pH are maintained to mimic physiological conditions.

Several hours later the oocytes are ready to be placed with the spermatozoa.
If the method ICSI is necessary, then the cells surrounding the oocytes are removed in order to inject the single spermatozoa into center of the oocyte.
If ICSI is not needed then the oocytes are added to culture medium containing approximately 100,000 spermatozoa.

The next day, whether “classic” IVF or ICSI has been performed, fertilization is confirmed by observing 2 pro-nuclei (one containing half the number of chromosomes from the mother, the other containing the other half from the father).

The fertilized oocytes (zygotes) are selected and further cultured until the day of embryo transfer either a) on the 2nd day (2-4 cell stages) b) 3rd day (6-8 cell stage) or c) 5th/6th day (blastocyst stage).

In some cases a small incision will be made in the outer protein coat surrounding the embryo to assist implantation. (Assisted Hatching).
If many oocytes are fertilized and are of “good quality” the surplus of embryos may be frozen for a possible future attempt.
The embryo transfer is a painless procedure, performed without anesthetic-usually taking 5-10 minutes and can be likened to a simple PAP test. The embryos are placed in a catheter and introduced into the uterus vaginally.
The number of embryos replaced depends on their “quality”, age of the patient and outcome of previous IVF attempts.