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IVF procedure

Details the fertilization of the egg and sperm in IVF.

Fertilization (Fertilisation)

The term in-vitro fertilization is derived from Latin in-vitro meaning glass because the eggs are fertilized in laboratory glassware. On the day of egg collection, the male partner is asked to provide a semen sample. He collects his semen by masturbation unless there has been other arrangements.

The sperm is washed in a culture medium and prepared in order to separate the sperm from seminal plasma.  If a donor sperm is to be used, the sample will then taken from the freezer, thawed and prepared.

Sperm are seperated from seminal plasma.

The eggs are collected into a specially prepared culture medium and once collected, they are examined under the microscope and each is graded for maturity, the maturity of an egg will determine when the sperm will be added to it. The eggs are then placed in the incubator at 37 C with 5% CO2 for a period of time (about 3-8 hours) before it is mixed with the selected sperm.

Between 20000-30000 sperm are mixed with each egg in a drop of specially prepared culture medium. This medium is prepared in a labeled dish that is kept in the incubator to allow fertilization to occur. The first sign of fertilization is the presence of two small dots inside the egg so-called “two- pronucleate” and the fertilized egg is called zygote. The two pronuclei, one came from the sperm and one came from the egg. Occasionally the egg is fertilized abnormally with more than two pronuclei. Although this embryo may go on to divide, they are not viable and should not be replaced. Usually about 60-70% of the eggs collected will be fertilized, but this can vary from 0% to 100%. Regrettably, some 5-10% of couples will not achieve fertilization of any eggs. This could be due to, sperm lacking the fertilizing capacity, or poor egg quality or poor culture medium. However, in about 50% of the cases there is no obvious cause. If this happens, the couple would be advised to have ICSI in a subsequent cycle.

It takes about 18 hours for the egg to be fertilized, about 12 hours later the fertilized egg start to divide into two cells, and subsequently into four and so on. After about 48-72 hours from the egg collection, the embryos will usually consist of 4-8 cells each, and ready for replacement into the woman’s uterus. There is no significant difference in the expected pregnancy rates if the embryos are replaced on day two or three after egg collection. The couple can elect to allow the embryos to undergo further development to the balstocyst stage (usually this is achieved by day 5). Quoted pregnancy rates are significantly higher when good quality blastocysts are transferred.

Sometimes, the embryos fail to develop even though they have fertilized normally and in this case; a transfer would not be made.

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