Intracytoplasmic sperm injection (ICSI) is an in vitro fertilization procedure in which a single sperm is injected directly into an egg. Defective sperm function remains the single most important cause of human infertility.
ICSI is a further advancement over conventional IVF. IVF is unlikely to succeed in case of male factor infertility e.g. when sperm count is low or quality of spermatozoa is such that they are not capable of penetrating the egg. This is when Intracytoplasmic Sperm Injection (ICSI treatment) is recommended. ICSI can also be used if the male partner has previously had a vasectomy. It is part of the IVF treatment cycle, and the main difference is the technique we use to achieve fertilization.
How does ICSI work?
A single sperm is injected into each egg, using very fine micro-manipulation equipment. As the human egg is one tenth of a millimeter in diameter and the sperm 100 times smaller, this is a very delicate procedure performed by highly skilled embryologist under a sophisticated microscope. This technique of ICSI is used when sperms are not present in the semen, and they have to be obtained surgically from male reproductive tract.
There is some suggestion that birth defects are increased with the use of IVF in general, and ICSI specifically, though different studies show contradictory results. In a summary position paper, the Practice Committee of the American Society of Reproductive Medicine has said it considers ICSI safe and effective therapy for male factor infertility, but may carry an increased risk for the transmission of selected genetic abnormalities to offspring, either through the procedure itself or through the increased inherent risk of such abnormalities in parents undergoing the procedure. Test-tube babies have higher rates of birth defects, and doctors have long wondered: Is it because of certain fertility treatments or infertility itself? A large new study from Australia suggests both may play some role. Compared to those conceived naturally, babies that resulted from simple IVF, or In-vitro fertilization (mixing eggs and sperm in a lab dish) had no greater risk of birth defects once factors such as the mother’s age and smoking were taken into account. However, birth defects were more common with ICSI, especially if male factor is involved. About 10 percent of babies born this way had birth defects versus 6 percent of those conceived naturally.
This procedure is most commonly used to overcome male infertility problems, although it may also be used where eggs cannot easily be penetrated by sperm, and occasionally in addition to sperm donation. It can be used in severe defect of spermatozoa, because once the egg is fertilized, abnormal sperm morphology does not appear to influence blastocyst development or blastocyst morphology. Even with severe teratozoospermia, microscope can still detect the few sperm cells that have a normal morphology, allowing for optimal success rate.
ICSI is generally performed following an in vitro fertilization procedure to extract one to several oocytes from a woman. In ICSI, IVF male partner or the donor needs to provide a sperm sample on the same day when your eggs are collected. The sample will be checked in the lab, and if there is no sperm in his semen, doctors will extract sperm from epididymis or testicle. The extraction of sperm from epididymis is also known as percutaneous epididymal sperm aspiration (PESA) and extraction of sperm from testicle is also known as Testicular Sperm Aspiration (TESA). The procedure is done under a microscope using multiple micromanipulation devices (micromanipulator, micro injectors and micropipettes). A holding pipette stabilizes the mature oocyte with gentle suction applied by a micro injector. From the opposite side a thin, hollow glass micropipette is used to collect a single sperm, having immobilized it by cutting its tail with the point of the micropipette. The oocyte is pierced through the oolemme and directed to the inner part of the oocyte. The sperm is then released into the oocyte. The pictured oocyte has an extruded polar body at about 12 o’clock indicating its maturity. The polar body is positioned at the 12 or 6 o’clock position, to ensure that the inserted micropipette does not disrupt the spindle inside the egg. After the procedure, the oocyte will be placed into cell culture and checked on the following day for signs of fertilization. In contrast, in natural fertilization, sperms compete with one another to enter the oocyte and when the first sperm (considered to be most competent one) penetrates the oolemma, the oolemma hardens to block the entry of any other sperm. Concern has been raised that in ICSI, this sperm selection process is bypassed and the sperm is selected by the embryologist without any specific testing. However, in mid-2006, the FDA cleared a device that allows embryologists to select mature sperm for ICSI based on sperm binding to hyaluronan, the main constituent of the gel layer (cumulus oophorus) surrounding the oocyte. The device provides microscopic droplets of hyaluronan hydro gel attached to the culture dish. The embryologist places the prepared sperm on the microdot, selects and captures sperm that bind to the dot. Basic research on the maturation of sperm shows that hyaluronan-binding sperms are more mature and show fewer DNA strand breaks and significantly lower levels of aneuploidy than the sperm population from which they were selected. A brand name for one such sperm selection device is PICSI. A recent clinical trial showed a sharp reduction in miscarriage with embryos derived from PICSI sperm selection. ‘Washed’ or ‘unwashed’ sperm may be used in the process. Using ultra-high magnification during sperm selection (with the technique being called IMSI) has no evidence of increased live birth or diminished miscarriage rates compared to standard ICSI.
Success or failure factors:
One of the areas in which sperm injection can be useful is vasectomy reversal. However, potential factors that may influence pregnancy rate (and live birth rates) in ICSI include level of DNA fragmentation as measured e.g. by Comet assay, advanced maternal; age and semen quality.