Science commentary

what is involved in intracytoplasmic sperm injection?

Abi Berger, Science editor. 

BMJ

Intracytoplasmic sperm injection is a technique that increases the chance of conception in cases of severe male infertility or in cases in which the reasons for infertility remain unexplained. There are 59 centres in the United Kingdom licensed to conduct intracytoplasmic sperm injection.

Intracytoplasmic sperm injection involves injecting a single sperm into the centre of an ovum using a fine glass needle (one fourteenth the size of a human hair). The sperm can be collected from ejaculate or directly from the testis or epididymis; collection from the testis or epididymis is usually performed under general anaesthesia. Just before injection, the sperm is carefully prepared by washing off the seminal plasma; the best quality sperm are identified by washing through a special filter. Abnormally shaped sperm and those with poor motility are rejected. The chosen sperm is then concentrated in a tiny volume of culture fluid.

The woman undergoes ovarian stimulation, and then has ova collected as with in vitro fertilisation. The cumulus cells that surround the ovum are removed. The selected sperm is immobilised just prior to injection. Without this step, the ovum could be damaged by the beating of the tail of the sperm. It takes just a minute to inject the sperm directly into the ovum. Although the steps taken to obtain ova are the same as in routine in vitro fertilisation, intracytoplasmic sperm injection replaces the insemination stage. About 65% of the ova injected are likely to be fertilised normally but, as with in vitro fertilisation, some will fail to develop and some embryos may not be of good quality. Placement of the embryo in the woman occurs in the same manner as for in vitro fertilisation.

Intracytoplasmic sperm injection can be used to overcome most cases of male infertility, even those in which the cause of infertility is unknown. Sperm injection can also be used to treat cases of infertility that have a genetic cause such as a chromosomal abnormalitychiefly translocations or severe Klinefelter's syndrome; genetic causes account for up to 10% of problems with sperm. This method can also be used to treat carriers of cystic fibrosis, who may not have a vas deferens (Tuerlings JH et al, Fertility and Sterility 1998;69:899-903).

Sperm injection has also proved useful for men with testicular failure. Many men who have been diagnosed with testicular failure actually have tiny islands of normal spermatogenesis in their testes. By taking multiple fine needle aspirate biopsies of a testis to identify these islands, and by using the micromanipulation techniques of intracytoplasmic sperm injection to obtain their sperm, many men who have previously been told that they were infertile have managed to father children.

Although sperm injection offers hope for these men, there is concern that any genetic abnormality which may be as yet unidentified could unwittingly be passed on to their offspring. For this reason, centres that offer sperm injection recommend careful genetic counselling before a couple goes ahead with the procedure. The procedure itself could also carry a small risk. Since it involves piercing the outer and inner membranes of the ovum, and introducing a needle into the ovum, it is possible that the development of the embryo may be disturbed (Storeng RT et al, Acta Obstetricia et Gynecologica Scandinavica 1998;77:191-7).There is also an increased risk of chromosomal abnormalities in the sperm of men who have problems with their sperm. Both of these factors may have contributed to early findings that the risk of abnormalities in the sex chromosomes (which can cause infertility) is increased by about 0.5% in offspring born as a result of intracytoplasmic sperm injection (Bonduelle M et al, Human Reproduction 1996;11:131-55).