A single sperm is injected into each egg, using very fine micro-manipulation equipment. As the human egg is one tenth of a millimetre 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.
ICSI is done under an inverted microscope using micro manipulation technique. 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 immobilised it by cutting its tail with the point of the micropipette. Micropipette is used to pierce the oocyte through the oolemma and its tip is directed to the inner part of the oocyte (cytoplasm). 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 in the 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 hydrogel 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.
Potential factors that may influence pregnancy rates and live birth rates in ICSI include level of DNA fragmentation (as measured by Comet assay) advanced maternal age and semen quality.
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.