All pregnancies begin with the joining together of a single sperm and egg, this process is known as fertilisation. The single cell that results will usually go on to develop into an embryo and hopefully later a baby. This would normally take place in the woman’s Fallopian tubes, which allow eggs to pass from the ovaries into the womb. With in-vitro fertilisation (IVF), fertilisation is allowed to happen by mixing each egg with a number of prepared sperm in a test tube (hence the name “Test-Tube Baby treatment”). Whilst this has obviously been a major advance in the treatment of infertility it can almost be considered as simply changing the site for fertilisation and all other major steps remain the same.
Unfortunately for a number of couples their infertility can be due to a problem with fertilisation itself. Usually this is due to either:
- A low number of sperm – about 100,000 are required normally to have a reasonable chance of fertilising each egg.
- A fault in the way the sperm works – either the sperm do not move properly or have difficulty in binding to the egg.
Such cases are referred to as male factor infertility and can often be predicted from a sperm count alone, before any attempt is made at infertility treatments or where there is known to be a blockage in the male reproductive organs. Occasionally couples will be found to have a problem with fertilisation at their first attempt at IVF, this is after all the only chance we get to observe the sperm and egg together. The problem may lie with either the sperm, even though the sperm analysis was normal, the egg or both. If the number of eggs that fertilise (the fertilisation rate) is very few or none at all (failed fertilisation) then further attempts at IVF are usually going to fail also.
If a problem with sperm numbers, function or fertilisation is expected then usually the recommended treatment is a special form of IVF called Intracytoplasmic sperm injection.
Intracytoplasmic Sperm Injection (ICSI for short) is a technique which involves the injection of a single sperm into an egg and so bypasses all the normal steps in fertilisation. For further information see our patient information leaflet.