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ICSI (intracytoplasmic sperm injection) is arguably the biggest advance in assisted reproductive technology since the successful birth of Louise Brown, 21 years ago.
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ICSI (intracytoplasmic sperm injection) is arguably the biggest advance in assisted reproductive technology since the successful birth of Louise Brown, 21 years ago. However, with any new techniques, the possible risks including short and longterm health consequences of the offspring must be considered. Thus far, the outcome data regarding ICSI offspring has been reassuring. However, many theoretical concerns regarding ICSI have been raised, and the validity of such concerns may take years, or even generations, to address. Any possible risks of ICSI seem to be outweighed by the benefits in treating males with severe male factor infertility, where the couple=s only alternative is sperm donation. Less clear, however, is the wisdom of applying ICSI to all IVF cycles; that is, in cases where natural fertilization is expected to occur at normal rates.
ICSI for All IVF Cycles
There is little data comparing IVF to ICSI in non-male factor cases. Utilization of ICSI is increasing worldwide in situations where it is not essential for successful fertilization. In some large clinics, more than 60% of all cycles are ICSI, and in still others, ICSI is already routine for all IVF treatment cycles. One obvious advantage of to the application of ICSI routinely is the near avoidance of unexplained fertilization failure. Some have suggested its use in cases with low egg numbers or advanced reproductive age to maximize fertilization. The assessment of oocyte maturity and dysmorphisms is certainly better assessed by ICSI, and this data may be used to gain insight into oocyte quality and the appropriateness or effec tiveness of the stimulation protocol used. ICSI is also advantageous when used in conjunction with preimplantation genetic diagnosis, particularly polar body biopsy.
Proposed Concerns Regarding Routine Application of ICSI
While ICSI has unarguably revolutionized the treatment of male factor infertility, critics question its potential for a negative impact on the genetic composition of future generations. ICSI bypasses the biological mechanisms of sperm selection put in place by evolution. Furthermore, ICSI in the human was not preceded by adequate animal research. The application of ICSI in humans has, in fact, represented the experimental model. ICSI provides the ability to improve the reproductive potential of mutant male genotypes with the resulting possibility of altering the genetic composition of future human populations.
Chromosomal Abnormalities and Male Infertility
The incidence of chromosomal abnormalities in infertile men is 5.8% compared to 0.38% in phenotypically normal male newborns. In another review of cytogenic studies in azoospermic and oligospermic men, chromosomal abnormalities were found in 13.7% and 4.6% of these groups, respectively. Klinefelter’s syndrome and Klinefelter’s mosaic were predominant abnormalities mentioned. Non-Klinefelter’s sex chromosome abnormalities and autosomal abnormalities were observed in 1.8% and 1.1% of azoospermic males, respectively. In oligospermic men, autosomal abnormalities were present in 3% of the population and sex chromosome abnormalities in 1.6%. Indeed, Palermo has recently reported two successful pregnancies in Klinefelter’s patients using testicular sperm extraction in combination with ICSI.
Y chromosome micro deletions have a frequency in azoospermic and oligospermic males of 9% to 18%. Translocations can also be found in men with poor semen production with a resulting increase in trisomic offspring. Congenital bilateral absence of the vas deferens is caused by a mutation of the cystic fibrosis transmembrane regulator gene (CFTR). In such cases, the female partner must be screened for CF mutations to avoid producing an affected child. CFTR mutations have also been found with a prevalence of 13% in men with decreased semen parameters and an intact vas deferens.
Sakkas has proposed that the use of blastocyst culture to allow the selection of the most viable embryo post embryonic genome activation might overcome any paternal genome defects which might be introduced through ICSI. Concerns Related to the ICSI Technique Itself
Mitochondrial DNA is inherited exclusively from the oocyte. Therefore, mDNA from the sperm must be eliminated at early stages of fertilization. When ICSI is used, the entire sperm, including the plasma membrane, is injected. This could hinder recognition and subsequent elimination of paternal mitochondrial DNA.
Hewitson raised other concerns regarding the ICSI technique in a study involving primates. Oocytes are typically aligned with the polar body at 6 or 12 o’clock during injection so as to avoid damage to the second miotic spindle. It is assumed that the polar body is in close approximation to the spindle. However, in Hewitson’s study of the Rhesus monkey, the spindle may, in fact, reside as far as 68 degrees from the polar body, and in the human the polar body on average was 56 degrees from the spindle (range 23-95). The damage to the miotic spindle may therefore be more common than previously thought.
The same group also demonstrated that sperm nuclear decondensation is atypical after ICSI. The apical region remains condensed longer than the basal region. Chromosomal abnormalities could therefore be related to this delay in decondensation. Incomplete decondensation of chromosomes in this region could lead to asymmetrical segregation at mitosis. The X chromosome is preferentially located in the apical region ¾ a possible explanation of the increased incidence of sex chromosome abnormalities in ICSI offspring.
There are many other differences between ICSI and conventional IVF that could contribute negatively to the ultimate outcome of ICSI. The natural selection of normal fertilization is bypassed by biologists who choose a single sperm. Significant physical distortion occurs during the injection procedure, and the use of hyaluronidase to remove cumulus-corona cells, as well as the use of PVP for the injection medium represents potentially adverse physiologic stress to the oocyte. The fate of an intact acrosome and the potential toxicity of its enzymes has not been adequately evaluated. Important proteins (e.g., gamma-tubulin) critical to the formation of the sperm aster are present at the cortex of the oocyte. By placing the sperm in the center of the egg during ICSI, the normal choreography of the sperm and egg nuclei may be altered.
Longterm concerns regarding ICSI offspring include cancer rates in later years of life, reproductive potential, alterations in the pattern of genomic imprinting, and the congenital malformation rate in children of ICSI babies. These concerns will not be addressed for years to come.
Prospective Follow-up of Pregnancies from ICSI
2375 ICSI pregnancies resulting in 1987 children from cycles between April 1991 and September 1997 were assessed by the Belgium group. Major malformations were seen in 2.3% of ICSI offspring, similar to most general population registries and ART surveys. A 1.6% incidence of de novo chromosomal abnormalities, with one-half being sex chromosomes and the other half being autosomal, were also described. Statistically significant increase in the sex chromosome abnormality rate was seen when compared to the literature. A study to assess the mental and psychological development of children up to the age of 2 found no differences between ICSI offspring and naturally conceived children.
From Cornell, Palermo compared 1753 IVF newborns to 1732 ICSI babies. Major malformations were seen in 1.8% of IVF babies compared to 1.1% of ICSI offspring. Minor malformations were present in 1.4% of IVF cases compared to 0.8% with ICSI.
Clinical Comparisons of IVF and ICSI
Some comparisons have been made regarding the outcome of oocytes fertilized conventionally by IVF compared to ICSI. Shoukir in 1998 described the development of supernumerary embryos to the blastocyst stage in patients who had transfers on day 2 following either IVF or ICSI. The percentage of spare embryos progressing to the blastocyst stage in IVF patients was 49%, while only 26% of embryos in the ICSI group progressed to the blastocyst stage. Aboulghar performed a randomized prospective trial comparing IVF and ICSI in tubal factor patients with normal semen parameters. The pregnancy and implantation rates were similar in both groups. However, the fertilization rate was significantly higher in the IVF group. ICSI appeared to have no advantage in the treatment of tubal factor patients. Aboulghar also evaluated ICSI versus convention IVF for sibling oocytes in both unexplained infertility and borderline semen parameter cycles. In the unexplained infertility group, a similar fertilization rate, 63% with ICSI compared to 51% with IVF, was seen. However, total fertilization failure occurred in 5 of 22 cases with conventional IVF compared to 0 fertilization failures with ICSI. In the borderline semen group, fertilization rate with ICSI was 59% compared to 27% with IVF, and total fertilization failure occurred in 11 of 24 (46%) cycles compared to 0 cases in the ICSI group. Overall, 34% of patients were saved from a canceled embryo transfer due to total fertilization failure in cases of unexplained infertility or borderline semen parameters when ICSI was utilized. Hamberger evaluated patients with previous conventional fertilization failure. Fourteen of 42 (33%) patients saw no fertilization in a second cycle of IVF compared to no cases of fertilization failure in ICSI treated patients. Van Steirtethem described a small randomized trial of conventional IVF versus ICSI for sibling oocytes in tubal factor infertility. Significantly high fertilization was achieved in the ICSI group (68% versus 57%). However, the percentage of embryos cleaving and embryo quality was not significantly different. Total fertilization failure occurred in 4 conventional IVF patients versus 1 treated with ICSI. At the Colorado Center for Reproductive Medicine, we have reviewed our 1998 experience with conventional IVF compared to ICSI. In reviewing 153 ICSI cycles and 305 conventional IVF cycles, there appear to be no significant differences in the fertilization rate (56% versus 60%), the percentage of good quality day 3 embryos (52% versus 54%), pregnancy rate (61% versus 57%), the implantation rate (31% versus 32%), or the percentage of blastocyst formation (42% versus 46%).
In summary, ICSI appears to be neither helpful nor harmful when compared to conventional IVF in the treatment of non-male factor infertility. In cases of borderline semen parameters or unexplained infertility, there is a significant increase in the rate of fertilization with ICSI and a decrease in the incidence of total fertilization failure. Despite reassuring data regarding the outcome of ICSI offspring to date, potential long-term risks of the ICSI procedure are still to be determined. Therefore, it appears that the application of ICSI in all cases of IVF is unwarranted. Patients with unexplained infertility, borderline semen parameters, or severe male factor infertility are greatly benefitted by this technology, and the outcome data to date certainly support its continued use.
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