Results and factors affecting results of ICSI

One of the largest series reporting results using IVF/ICSI was from Van Steirteghem et al. at The Brussels Free University in Brussels, Belgium. In their preliminary report on 150 couples who underwent 150 consecutive treatment cycles, 1409 oocytes were injected and 830 were successfully fertilized for a fertilization rate of 59 percent. A total clinical pregnancy rate of 35 percent was achieved. The fertilization rate in this study was not influenced by the standard semen characteristics of concentration, motility, and strict criteria morphology. In another largest case serie on ICSI in the United States, Palermo et al. at Cornell reported successful fertilization in 1,142/1,923 (59 %) metaphase II oocytes injected, and ongoing pregnancies in 84/227 (37%) couples. Neither semen quality nor the source of sperm (ejaculated, surgically retrieved or electroejaculated) affected fertilization rates. They concluded that IVF/ICSI offers fertilization and pregnancy rates comparable to that achieved with normal sperm quality for couples who have failed to achieve fertilization on repeated IVF cycles or have severe impairments in semen quality. In addition, the success of IVF/ICSI was independent of standard semen parameters (density, motility, and morphology).

Factors Affecting Results Of ICSI
1. Spermatozoal factors: Nagy et al. evaluated the effect of spermatozoal factors on results of ICSI in 966 microinjection cycles. Despite no normal forms in a semen preparation, virtual azoospermia or essentially no motile sperm in the ejaculate, pregnancy could still be achieved. Nagy et al. found that the only absolute criterion for successful ICSI is the presence of at least one viable spermatozoon to inject per oocyte in the prepared pellet of the washed semen sample. The only category in which semen parameters had a significantly impaired fertilization and pregnancy rate was when there was no motility of sperm’o. If no motility is present, then viability is often impaired as well.

2. Female factors: Oehninger et al. investigated the role of matemal factors in a total of 92 couples, where 1163 oocytes were injected with an overall fertilization rate of 61 percent. Fertilization rates were unaffected by matemal age, but pregnancy rates were significantly lower with increased matemal age. Pregnancy rates were 49, 23 and 6 percent for couples in whom matemal age was <34, 35-39, and < 40 years. Similar results were found by Sherins et al., with a 30% pregnancy rate for the youngest couples and 13 % pregnancy rate for the couples with the oldest female partners. The rate of aneuploidy increases dramatically for embryos derived from the oocytes of women over 40 compared to those from women less than age 35. Therefore, it is likely that the chance of fertilization is unrelated to female factors, but that the chance of pregnancy occurring after ICSI is related primarily to oocyte factors, if a viable sperm is injected.

3. Oocyte activation: Since oocyte activation normally occurs in association with sperm binding, fusion and penetration of the oocyte, oocyte activation during intracytoplasmic may not necessarily occur. The importance of intentional induction of oocyte activation was demonstrated by Tesarik and Sousa who increased fertilization and pregnancy rates during ICSI with aggressive aspiration and injection of the oocyte cytoplasm. Direct comparison of gentle and vigorous cytoplasm aspiration resulted in an increase in fertilization rates per oocyte from 38% to 80% with increased pregnancy rates up to 52 % with aggressive aspiration/injection. Evaluation of calcium fluxes in oocytes during injections demonstrated an additional peak of intracellular calcium levels for aggressive aspiration, when compared with gentle aspiration. Intracellular calcium changes have long been thought to have a role in oocyte activation. An additional sperm factor may have a role in cytoplasmic activation. Aggressive immobilization of spermatozoa has been used to effect increased sperm membrane permeability. Gerris et al. evaluated the effects of sperm tail breakage on ICSI success by directly comparing fertilization rates achieved using sperm with intact tails compared to sperm with damaged tails. Aggressive immobilization of spermatozoa resulted in an increase in the percentage of normally fertilized oocytes from 36 to 60%. These authors and others” suggested that tail damage induces sperm membrane changes which facilitate biochemical events necessary for sperm nuclear decondensation and pronuclear formation. Palermo et al. have also investigated the effect of aggressive sperm immobilization on fertilization and pregnancy rates. Although there was little improvement in fertilization rates for ejaculated sperm, a dramatic improvement in epididymally-retrieved sperm fertilization rates was seen, from 51 to 84% per oocyte, with an associated increase in pregnancy rates from 5 1 to 82 %. The biochemical basis for the effect of increased sperm membrane permeability to improve fertilization rates is unclear. It is possible that increased permeability of the manipulated sperm resulted in better penetration of ooplasmic factors into the spermatozoon to induce male pronuclear formation. Alternatively, it is possible that increased permeability results in enhanced leakage of toxic factors out of the cytoplasmic droplet of immature epididymal spermatozoa.

4. Cytoplasmic Injection/oocyte injury: Disruption of the oocyte sufficient to cause oocyte demise may occur during ICSI. Results from some of the major centers performing ICSI show rates of oocyte loss after injection of 7 to 14 percent. Although the precise reasons for oocyte injury are not known, it is though to occur as a result of plasma membrane and ultrastructural disturbances associated with injection, damage to the meiotic spindle during injection, and/or extrusion of the oocyte cytoplasm following injection. In addition, other factors such as changes in temperature have been reported to cause irreversible changes in the meiotic spindle of the human oocyte. Clearly, there is a learning curve for embryologists performing the ICSI procedure. As greater expertise is gained, the oocyte injury rate decreases. Palemo et al. have recently described oocyte characteristics that may predispose to oocyte injury. These investigators described an oocyte membrane response of “sudden breakage” during attempted ICSI. The oocytes with this response did not form a normal oocyte membrane funnel around the injection pipette. Instead, the oocyte membrane separated, spilling the oocyte cytoplasm and resulting in a 14 % injury rate, compared to a 4 % injury rate for other oocytes. Oocytes demonstrating sudden breakage were more likely to be retrieved from women who received higher gonadotropin treatment doses, with lower serum estradiol levels at retrieval, yielding immature oocytes, including those requiring maturation in vitro. These observations suggest that ovarian stimulation characteristics may affect the ability of oocytes to successfully undergo ICSI.