ICSI is a modified form of in vitro fertilisation (IVF). Treatment for the female partner is the same as for IVF; she is given hormone injections each day to stimulate her ovaries to produce quite a few eggs at once. These are then collected so that they can be fertilised in the laboratory by the male partner’s sperm.
In a standard IVF procedure, the man’s sperm is collected by masturbation about three hours before the woman’s eggs are collected. The sperm are washed and spun at high speed to select the sperm that are the most active as these are considered the best quality. If the man does not produce many sperm in his ejaculate, or none at all, intracytoplasmic sperm injection may be a good idea.
The advantage of intracytoplasmic sperm injection is that it only requires one sperm to fertilise each of the female’s eggs, so if the number of sperm is very low, this type of fertility treatment is still possible. Rarely, a man may produce no sperm at all because of blocked tubes in the testes. In this case, sperm can be surgically removed from inside the testes for use in intracytoplasmic sperm injection.
The actual process of intracytoplasmic sperm injection involves literally injecting the DNA from the head of one sperm directly into a mature egg in the laboratory. This is a delicate procedure that must be done without damaging the egg. Once the sperm DNA meets with the egg, fertilisation can occur. This does not happen with every intracytoplasmic sperm injection, but a fertilisation rate of about 80 % is not unusual. This is, of course, only the first step and the success rate of intracytoplasmic sperm injection, the proportion of pregnancies that results from treatments, is much lower.
The fertilised eggs are then cultured in the same conditions as those derived from standard in vitro fertilisation. Once they are 2–3 days old, the best one, two or three can be chosen for transfer into the female partner’s uterus. If several embryos look particularly healthy, they may be cultured until 5–6 days after the intracytoplasmic sperm injection, when some of them may become balls of cells called blastocysts. The embryos transferred at this stage have a slightly higher chance of implanting in the uterus to bring about pregnancy.
The overall success rates for intracytoplasmic sperm injection are similar to those for IVF without ICSI. Around 35 % of women under 35 who have ICSI become pregnant; this reduces to 28.5 % for women aged 35 to 37 and then drops steadily as the age of the woman rises.