Conventional in vitro fertilization (IVF) involves placement of tens of thousands of moving sperm with each egg in a culture dish. The sperm penetrates the egg in a natural way to cause fertilization. If recognized sperm abnormalities predict failure of fertilization in vitro, intracytoplasmic sperm injection (ICSI) may be recommended.
ICSI is an alternate means of fertilization often used to treat male infertility in which the sperm is injected into the egg. Examples of sperm abnormalities that may require ICSI are low sperm numbers, decrease in sperm movement, a high number of abnormal sperm forms, or history of previous fertilization failure with conventional IVF. In addition, sperm subjected to cryopreservation (freezing) and thawing, or sperm recovered surgically from the testis (testis biopsy) may also require ICSI.
ICSI is performed with the aid of a microscope to visualize the sperm and egg, and with micro-tools constructed from small glass tubes. One micro tool is blunt and holds the mature egg. The other micro tool is drawn to a sharp point that is used to capture the sperm and inject it into the egg. Approximately 95% of mature eggs survive the process of ICSI.
The percent of eggs fertilized by ICSI will vary widely based on sperm and egg quality. An average fertilization rate would be 70% when the results from many patients are compiled, but the fertilization rate of the eggs recovered from any one patient varies broadly from 0-100%. Following fertilization by ICSI, the eggs will be handled in the same manner as described for IVF by conventional insemination.
ICSI is a relatively new procedure (invented in the early 1990’s). It has become a standard-of-care therapy internationally despite the limited long-term follow up of the babies conceived with this technology. Children produced as a result of ICSI may have birth defects and congenitally acquired anomalies. A number of recently reported studies indicate that the incidence of birth defects after ICSI is slightly greater than in the general population. It is unclear whether ICSI increases the risk of birth defects greater than conventional IVF.
It is controversial whether infertile couples as a group have more offspring with defects regardless of what kind of therapy is used to help them become pregnant. In an uncertain percentage of cases, male children will inherit the father’s inability to produce sperm in a normal fashion. Genetic testing during early pregnancy may be appropriate in selected cases.