ICSI Overview: Intracytoplasmic sperm injection (ICSI) is a technique used in the IVF laboratory to inject individual sperm into eggs. The procedure was developed in Belgium in the early 1990's (Palermo et al., 1992) and it revolutionized the treatment of male factor infertility. Prior to ICSI, men with moderate and severe fertility issues had little or no chance of having their own genetic children. ICSI has so revolutionized the treatment of infertility that it is used in the majority (55.6%) of assisted reproductive technology cycles in the United States (CDC National Summary and Fertility Clinic Reports, 2003).
When IVF is performed without ICSI, it is common to incubate individual oocytes in a petri dish with about 100,000 sperm. Usually these sperm have been obtained by processing the semen in such a way as to be able to isolate sperm that look normal and swim energetically. Only the best 10% of the sperm in a normal semen sample are used, and in the petri dish, these compete for the honor of fertilizing the oocyte.
When ICSI is employed, individual sperm are isolated and forcibly injected into the oocyte by an embryologist. The oocytes have to be incubated in the enzyme hyaluronidase to remove the cumulus cells that surround them (naturally, these cells would be dislodged by the many sperm that try to penetrate the oocyte). Prior to injection, the sperm may be processed (as above) but often there are so few sperm available that processing is minimal. Once selected, the sperm is immobilized by breaking its tail. This is accomplished by dragging the injection needle across the tail until a visible kink or break can be seen. The immobilized sperm is then aspirated into the needle, which is pushed through the shell surrounding the oocyte and then through the cell membrane. The elasticity of the oocyte membrane is such that the embryologist must be rough with it to get through. Piercing the membrane is usually achieved either by poking it several times or by aspirating the membrane into the needle until it breaks. Once the membrane breaks, the sperm can be dropped inside the oocyte.
Technically, ICSI is one of the most difficult procedures to perform in the IVF laboratory and it requires a talented embryologist to do it well. As well as being responsible for choosing “the sperm”, the embryologist must work quickly and be firm enough to break the sperm tail and oocyte membrane while not being so aggressive as to kill the oocyte. ICSI has been so successful as a technique that it is now widely used in cases where there is no male factor infertility. In fact, of all the ICSI cases performed nationally in 2003, only 53% had a male issue (CDC, 2003). While ICSI is absolutely indicated for low sperm counts, decreased sperm motility, abnormal sperm morphology (size and shape) and surgically retrieved sperm, its use has expanded to include cases with anti-sperm antibodies, previous low fertilization with IVF, low oocyte numbers, frozen-thawed sperm and ejaculatory dysfunction such as retrograde ejaculation. In addition, ICSI is being widely used for patients having preimplantation genetic testing because it avoids DNA contamination during embryo biopsy by the many sperm that are usually attached to the shell of the embryo.
ICSI Risks: In assessing the risks of ICSI, we must first look at the procedure itself. In piercing the cell membrane, our greatest concern is in avoiding the area within the oocyte where the DNA is located. This is done by orientating the oocyte such that the polar body (a small packet of discarded DNA) is placed at the 12 or 6 o'clock position and the needle inserted at 3 o'clock. The polar body is the most practical indicator of where the oocyte DNA is located since it is created by the division of the oocyte's total DNA just prior to ovulation. However, the DNA may not always be in the assumed place so a theoretical risk of damage exists, and chromosome breakage has been observed as being higher in ICSI-derived embryos when compared to conventional IVF embryos (Bergere et al., 1995; Edirisinghe et al., 1997).
In addition to DNA disruption or damage, the physical and biochemical disturbance that occurs could be significant. The injection procedure could introduce foreign material into the oocyte such as culture medium, seminal fluid with or without bacteria (Michelmann et al., 1998), viruses (Brossfield et al., 1999), or in theory, even prions (Lacey & Dealler, 1994) or foreign DNA.
Following the ICSI procedure, the fertilization process is known to be different than with conventional IVF with atypical decondensation of the sperm head resulting in delayed replication of the male genome. This is thought to result from the injection of the intact sperm into the oocyte since such sperm retain their acromosomal cap and perinuclear theca, both of which are normally lost as the sperm penetrates the shell of the oocyte. There is marginal evidence that the sperm sex chromosome is preferentially located in the anterior head and therefore might be impacted by the delayed decondensation caused by retention of the cap (Luetjens et al., 1999).
Currently there is no evidence that the miscarriage rate is different between ICSI and IVF pregnancies, and the incidence of prematurity and low birth weight babies (7.6% and 10.3% respectively for ICSI) is similar to that for IVF in large studies (Wisanto et al., 1995; Aytoz et al., 1998), but slightly higher than rates found in natural pregnancies. These outcomes have been confirmed in a large US-based study (Schieve et al., 2002) showing overall lower birth weight and higher perinatal mortality in children conceived with the help of reproductive technologies, but no significant differences between ICSI and IVF.
In the mid 1990's ICSI had become a routine procedure in the world of assisted reproductive technology (ART) and was being widely used. However, reports surfaced indicating that the resulting children had a high incidence of chromosomal abnormalities (In 't Veld, 1995; Van Opstal et al., 1997). The immediate response from the ART community was a flurry of scientific papers refuting the findings, but ultimately the conclusions of the studies were confirmed by large scale, prospective systematic follow up studies on the ICSI children. Instrumental in these studies was the Brussels University where ICSI was invented. Thorough pre- and postnatal testing showed an abnormal karyotype in 2.6% of the ICSI pregnancies (Bonduelle et al., 1999) and in a subsequent study, 3% showed a chromosomal abnormality (Bonduelle et al., 2002). Novel chromosome abnormalities increased threefold (1.6% in ICSI vs. 0.5% in the general population) and these were mostly comprised of sex chromosome aneuploidies with a smaller number of autosomal structural anomalies. Inherited chromosomal abnormalities increased fourfold in ICSI pregnancies (1.4% compared to 0.3% in the general population) and this was related to the higher rate of existing chromosome abnormalities seen in the parents (mainly the fathers). It is important to point out that the incidence of these sex chromosome aneuploidies and structural abnormalities is inversely related to the number of sperm in the ejaculate and is therefore higher in ICSI fathers (4.8% vs. 0.5% in the general population), and interestingly also higher in ICSI mothers (1.5%: Van Assche et al., 1996). The structural chromosome abnormalities include deletions of sections of the Y chromosome in some men with low sperm counts which will be passed directly to sons created by ICSI.
We are fortunate that the children of ICSI are being widely followed and many solid studies have appeared and continue to appear on the incidence of congenital abnormalities (these are problems that cause impaired function and require medical or surgical intervention). The most common abnormality appears to be hypospadias (a urological condition where the urethra opens under the penis instead of at the tip, and which is correctable with minor surgery) which is increased in ICSI births (Wennerholm et al., 2000). However, when evaluating these cases, the increased risk for congenital abnormalities is often reduced or eliminated when confounding factors (maternal age, infertility, multiple pregnancy, familial and pregnancy history) are factored in (Ericson & Kallen, 2001). Nonetheless, it does appear as though ICSI and IVF children do have an increased odds ration (2.77 and 1.8 respectively) for malformations that need medical or surgical intervention in early life when compared to naturally conceived children (Bonduelle et al., 2005).
Concerns have also arisen about developmental delays in ICSI children as a result of a single paper (Bowen et al., 1998) that had them scoring lower on the Bayley Scales of Infant Development at 1 year of age when compared to IVF and naturally conceived infants. However, a good number of solid papers have since been published indicating that this finding is not holding up and that ICSI children are performing normally in psychological testing as well as in their cognitive and verbal skills using the Bayley and other scales of intelligence (Bonduelle et al., 1998; 2003 Ponjaert-Kristoffersen et al., 2004; 2005).
Finally, it is worth asking if gene expression is normal for ICSI children and are problems likely to arise as the children get older? In looking at gene defects, there is emerging evidence that ART children might be at a higher overall risk for genomic imprinting errors when compared to naturally conceived children. Genomic imprinting is a process that silences one gene from a parent, specifically so that the gene inherited from the other parent can do the work. The classic example is placental growth, which is controlled largely by paternal genes. Maternal genes for placental growth are deliberately inactivated since it is considered a conflict of interest for Mom's genes to be involved in the regulation of how much of her resources the fetus gets. Problems arise when an imprinted gene is defective, because the perfectly good copy of the gene from the other parent has been switched off and therefore cannot work. Diseases such as Beckwith-Wiedmann and Angleman's syndromes result from not having a functioning copy of a gene and preliminary evidence suggests that these might be more prevalent in IVF children (Gosden et al., 2003). Abnormal spermatogenesis is associated with an increase in defective genomic imprinting (Marques et al., 2003), but it is probably too early to tell if imprinting errors will occur more frequently in ICSI children. Angleman's syndrome for example occurs at most at a rate of 1/200,000 IVF births, so the impact of ICSI will be difficult to measure. Similarly, retinoblastoma (a type of cancer of the eye that is caused by a genetic defect similar to what causes imprinted diseases) has been reported as slightly higher in IVF children (Moll et al., 2003) but further studies will be required to substantiate this observation and to ascertain the specific risk of ICSI.
ICSI is an aggressively invasive procedure that deposits a single sperm, usually from an infertile father, into the oocyte of a woman who has undergone fertility treatments. The specific risk of ICSI in offspring is an increased incidence of chromosomal abnormalities which may be caused by the procedure or by the parents, or both. ICSI is a routine and overly used procedure and patients should be educated as to the risks. Of the studies cited here, none of the children examined were older than 5 years. The long term hazards of the procedure, if any, remain to be determined. See below for the complete bibliography.
-- Joe Conaghan, PhD
Aytoz A, Camus M, Tournaye H, Bonduelle M, Van Steirteghem A, Devroey P. Outcome of pregnancies after intracytoplasmic sperm injection and the effect of sperm origin and quality on this outcome. Fertil Steril. 1998 Sep;70(3):500-5.
Bergere M, Selva J, Volante M, Dumont M, Hazout A, Olivennes F, Frydman R. Cytogenetic analysis of uncleaved oocytes after intracytoplasmic sperm injection. J Assist Reprod Genet. 1995 May;12(5):322-5.
Bonduelle M, Wilikens A, Buysse A, Van Assche E, Wisanto A, Devroey P, Van Steirteghem AC, Liebaers I. Prospective follow-up study of 877 children born after intracytoplasmic sperm injection (ICSI), with ejaculated epididymal and testicular spermatozoa and after replacement of cryopreserved embryos obtained after ICSI. Hum Reprod. 1996 Dec;11 Suppl 4:131-55.
Bonduelle M, Aytoz A, Van Assche E, Devroey P, Liebaers I, Van Steirteghem A. Incidence of chromosomal aberrations in children born after assisted reproduction through intracytoplasmic sperm injection. Hum Reprod. 1998 Apr;13(4):781-2.
Bonduelle M, Camus M, De Vos A, Staessen C, Tournaye H, Van Assche E, Verheyen G, Devroey P, Liebaers I, Van Steirteghem A. Seven years of intracytoplasmic sperm injection and follow-up of 1987 subsequent children. Hum Reprod. 1999 Sep;14 Suppl 1:243-64.
Bonduelle M, Van Assche E, Joris H, Keymolen K, Devroey P, Van Steirteghem A, Liebaers I. Prenatal testing in ICSI pregnancies: incidence of chromosomal anomalies in 1586 karyotypes and relation to sperm parameters. Hum Reprod. 2002 Oct;17(10):2600-14.
Bonduelle M, Ponjaert I, Steirteghem AV, Derde MP, Devroey P, Liebaers I. Developmental outcome at 2 years of age for children born after ICSI compared with children born after IVF. Hum Reprod. 2003 Feb;18(2):342-50.
Bonduelle M, Wennerholm UB, Loft A, Tarlatzis BC, Peters C, Henriet S, Mau C, Victorin-Cederquist A, Van Steirteghem A, Balaska A, Emberson JR, Sutcliffe AG. A multi-centre cohort study of the physical health of 5-year-old children conceived after intracytoplasmic sperm injection, in vitro fertilization and natural conception. Hum Reprod. 2005 Feb;20(2):413-9.
Bowen JR, Gibson FL, Leslie GI, Saunders DM. Medical and developmental outcome at 1 year for children conceived by intracytoplasmic sperm injection. Lancet. 1998 May 23;351(9115):1529-34.
Brossfield JE, Chan PJ, Patton WC, King A. Tenacity of exogenous human papillomavirus DNA in sperm washing. J Assist Reprod Genet. 1999 Jul;16(6):325-8.
Centers for disease control and prevention. Assisted reproductive technology success rates. National summary and fertility clinic reports 2003 2005 Dec; United States Department of Health and Human Services.
Edirisinghe WR, Murch A, Junk S, Yovich JL. Cytogenetic abnormalities of unfertilized oocytes generated from in-vitro fertilization and intracytoplasmic sperm injection: a double-blind study. Hum Reprod. 1997 Dec;12(12):2784-91.
Ericson A, Kallen B. Congenital malformations in infants born after IVF: a population-based study. Hum Reprod. 2001 Mar;16(3):504-9.
Gosden R, Trasler J, Lucifero D, Faddy M. Rare congenital disorders, imprinted genes, and assisted reproductive technology. Lancet. 2003 Jun 7;361(9373):1975-7.
In't Veld P, Brandenburg H, Verhoeff A, Dhont M, Los F. Sex chromosomal abnormalities and intracytoplasmic sperm injection. Lancet. 1995 Sep 16;346(8977):773.
Lacey RW, Dealler SF. Vertical transfer of prion disease. Hum Reprod. 1994 Oct;9(10):1792-6.
Luetjens CM, Payne C, Schatten G. Non-random chromosome positioning in human sperm and sex chromosome anomalies following intracytoplasmic sperm injection. Lancet. 1999 Apr 10;353(9160):1240.
Marques CJ, Carvalho F, Sousa M, Barros A. Genomic imprinting in disruptive spermatogenesis. Lancet. 2004 May 22;363(9422):1700-2.
Michelmann HW. Influence of bacteria and leukocytes on the outcome of in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI). Andrologia. 1998;30 Suppl 1:99-101.
Moll AC, Imhof SM, Cruysberg JR, Schouten-van Meeteren AY, Boers M, van Leeuwen FE. Incidence of retinoblastoma in children born after in-vitro fertilization. Lancet. 2003 Jan 25;361(9354):309-10.
Palermo G, Joris H, Devroey P, Van Steirteghem AC. Pregnancies after intracytoplasmic injection of single spermatozoon into an oocyte. Lancet. 1992 Jul 4;340(8810):17-8.
Ponjaert-Kristoffersen I, Tjus T, Nekkebroeck J, Squires J, Verte D, Heimann M, Bonduelle M, Palermo G, Wennerholm UB. Collaborative study of Brussels, Goteborg and New York. Psychological follow-up study of 5-year-old ICSI children. Hum Reprod. 2004 Dec;19(12):2791-7.
Ponjaert-Kristoffersen I, Bonduelle M, Barnes J, Nekkebroeck J, Loft A, Wennerholm UB, Tarlatzis BC, Peters C, Hagberg BS, Berner A, Sutcliffe AG. International collaborative study of intracytoplasmic sperm injection-conceived, in vitro fertilization-conceived, and naturally conceived 5-year-old child outcomes: cognitive and motor assessments. Pediatrics. 2005 Mar;115(3): 283-9.
Schieve LA, Meikle SF, Ferre C, Peterson HB, Jeng G, Wilcox LS. Low and very low birth weight in infants conceived with use of assisted reproductive technology. N Engl J Med. 2002 Mar 7;346(10):731-7.
Van Assche E, Bonduelle M, Tournaye H, Joris H, Verheyen G, Devroey P, Van Steirteghem A, Liebaers I. Cytogenetics of infertile men. Hum Reprod. 1996 Dec;11 Suppl 4:1-24.
Van Opstal D, Los FJ, Ramlakhan S, Van Hemel JO, Van Den Ouweland AM, Brandenburg H, Pieters MH, Verhoeff A, Vermeer MC, Dhont M, In't Veld PA. Determination of the parent of origin in nine cases of prenatally detected chromosome aberrations found after intracytoplasmic sperm injection. Hum Reprod. 1997 Apr;12(4):682-6.
Wennerholm UB, Bergh C, Hamberger L, Westlander G, Wikland M, Wood M. Obstetric outcome of pregnancies following ICSI, classified according to sperm origin and quality. Hum Reprod. 2000 May;15(5):1189-94.
Wisanto A, Magnus M, Bonduelle M, Liu J, Camus M, Tournaye H, Liebaers I, Van Steirteghem AC, Devroey P. Obstetric outcome of 424 pregnancies after intracytoplasmic sperm injection. Hum Reprod. 1995 Oct;10(10):2713-8.