Intracytoplasmic sperm injection

INTRODUCTION — Intracytoplasmic sperm injection (ICSI) refers to a technique in which a single sperm is injected directly into the cytoplasm of a mature oocyte. This procedure is performed as part of an in vitro fertilization (IVF) cycle and provides an effective method for assisting fertilization in men with suboptimal semen parameters or who experienced no or low fertilization rates after conventional insemination.

This topic discusses the indications, techniques, and outcomes for ICSI. Other discussions about male infertility, IVF, and outcomes with assisted reproductive technology are presented elsewhere.

●(See "Causes of male infertility".)

●(See "Approach to the male with infertility".)

●(See "Treatments for male infertility".)

●(See "In vitro fertilization: Overview of clinical issues and questions".)

●(See "Assisted reproductive technology: Pregnancy and maternal outcomes".)

In this topic, when discussing study results, we will use the terms "man/en" and "woman/en" as they are used in the studies presented. However, we encourage the reader to consider the specific counseling and treatment needs of transgender and gender diverse individuals.

DEVELOPMENT AND USE — ICSI was first applied to human gametes in 1988 [1]. It was initially used in cases of fertilization failure after standard IVF or when few sperm cells were available. The first pregnancies were reported in Belgium in 1992 [2]. ICSI is now used globally for treatment of both male factor and non-male factor infertility.

●Male factor infertility – In the setting of male factor infertility, ICSI has consistently demonstrated higher fertilization rates than prior micromanipulation techniques [2-5]. The capacity of ICSI to permit almost any type of spermatozoa to fertilize oocytes has made it the most successful treatment for male factor infertility. In the United States, the use of ICSI for IVF cycles has increased from 36.4 percent in 1996 to 76.2 percent in 2012 [6]. Globally, ICSI is a commonly employed technology and is responsible for the most treatment cycles per technique [7-9].

●Non-male factor infertility – ICSI cycles without male factor infertility have increased from 15.4 to 66.9 percent between 1996 and 2012 in the US [6].

INDICATIONS

Treatment of male factor infertility — ICSI is indicated primarily for treatment of male factor infertility [10]. In persons with male factor infertility, ICSI results in fertilization rates of up to 60 percent without a significant compromise to the pregnancy outcome. Pregnancy rates are highly influenced by the female factors, particularly maternal (or oocyte) age [11]. (See "In vitro fertilization: Overview of clinical issues and questions", section on 'What factors impact IVF success?'.)

Other indications — ICSI may be useful in the following clinical situations [10,12]:

●Failed fertilization in a prior IVF cycle

●HIV- or hepatitis-discordant couples (See "Use of assisted reproduction in HIV- and hepatitis-infected couples".)

●IVF cycles with low oocyte yield

●Need for preimplantation genetic testing of embryos in settings requiring absence of extraneous DNA contamination from other sperm. Examples include individuals with cystic fibrosis, BRCA mutations, and congenital adrenal hyperplasia.

•(See "Cystic fibrosis: Genetics and pathogenesis".)

•(See "Cancer risks and management of BRCA1/2 carriers without cancer".)

•(See "Genetics and clinical manifestations of classic congenital adrenal hyperplasia due to 21-hydroxylase deficiency".)

●Fertilization of previously cryopreserved oocytes and oocytes that have undergone in vitro maturation

●Treatment of borderline semen parameters

●Treatment of elected types of female infertility, such as individuals with some morphologic anomalies of oocytes and/or anomalies of the zona pellucida

Use of ICSI for all IVF cycles — While some IVF clinics choose to utilize ICSI for 100 percent of the cycles to reduce risk of total fertilization failure, this is not standard practice because of possibly lower live birth rates and concerns, both known and unknown, with the ICSI procedure.

●Possible impact on live birth rate – Lower live birth rates have been reported for ICSI cycles compared with conventional IVF alone but evidence is limited to observational data [10]. A retrospective cohort study of 317,996 ICSI cycles in couples without male factor infertility reported lower rates of implantation (23 versus 25 percent) and livebirth (36.5 versus 39.2 percent) compared with those undergoing conventional IVF [6]. However, further research is needed because other evidence suggests that ICSI improves fertilization rates and reduces total failed fertilization compared with conventional insemination in couples with well-defined unexplained infertility, both of which would be expected to improve live birth rates [13].

●Concerns regarding impact of ICSI procedure – While the overall risks of ICSI to the patient and offspring appear to be low, some clinicians prefer to use ICSI only as indicated above because of concerns for increasing the risk of both known and unknown outcomes.

•(See 'Outcomes' below.)

•(See "In vitro fertilization: Overview of clinical issues and questions".)

PRETREATMENT EVALUATION AND COUNSELING — Individuals who are considering ICSI are evaluated to identify all possible contributors to infertility and to understand the risk of transmitting infertility, and other chromosomal abnormalities, to children conceived by ICSI.

●Complete infertility evaluation – A thorough evaluation of the male patient, including semen analysis [14,15], sperm morphology [16], and urology consultation, is recommended. In males with severe oligospermia or azoospermia, additional testing may be warranted. (See "Approach to the male with infertility".)

●Discuss risk of chromosomal abnormalities – We inform patients considering ICSI of the risk of an abnormal fetal karyotype due to paternally inherited chromosomal abnormalities, the relatively benign phenotype of some of these chromosomal anomalies, and the risks associated with invasive prenatal diagnostic procedures so that they may make an informed choice about prenatal testing. There was no evidence of a higher risk of post-zygotic events leading to a higher proportion of chromosomal mosaicism from the ICSI procedure.

Preimplantation genetic testing (PGT) and prenatal testing for aneuploidy are reviewed in detail separately.

•(See "Preimplantation genetic testing".)

•(See "Prenatal screening for common aneuploidies using cell-free DNA".)

●Common genetic alterations associated with male infertility – The most common genetic factors associated with male infertility are cystic fibrosis gene mutations (associated with congenital absence of the vas deferens), structural chromosomal abnormalities (eg, aneuploidy, inversion, translocation) associated with impaired testicular function, and Y chromosome microdeletions (associated with impaired spermatogenesis).

•Structural chromosomal abnormalities – Structural chromosomal abnormalities in peripheral lymphocytes are observed in 10 to 15 percent of azoospermic men, 5 percent of oligospermic men, and less than 1 percent of normospermic men [17]. The partners of these men are at increased risk of miscarriage and progeny are at increased risk of congenital anomalies.

•Y chromosome microdeletions – Some guidelines recommend systematically screening men with azoospermia or severe oligozoospermia for chromosomal abnormalities, including Y chromosome microdeletions, which may be present in lymphocytes or detected only in sperm [18]. The American Society of Reproductive Medicine (ASRM) recommends that karyotyping be offered to men who have nonobstructive azoospermia or severe oligozoospermia (defined as less than 5 to 10 million sperm/mL) prior to performing ICSI with their sperm [19]. Neither the definition of severe oligozoospermia nor the recommendation for screening severely oligozoospermic men is consistent worldwide.

Detectable microdeletions of the Y chromosome are found by polymerase chain reaction in 10 to 15 percent of men with azoospermia or severe oligospermia. This is probably an underestimate since microdeletions that are nondetectable by current techniques likely exist. Male offspring of men with microdeletions will inherit the microdeletion and thus be at risk for infertility. The genetics of male infertility is discussed in detail separately.

-(See "Approach to the male with infertility".)

-(See "Causes of male infertility", section on 'Y chromosome and related defects'.)

-(See "Causes of male infertility", section on 'Autosomal and X chromosome defects'.)

•Cystic fibrosis – Cystic fibrosis is associated with a mutation of the cystic fibrosis transmembrane conductance regulator gene. Men who carry this gene may not have the classic clinical manifestations of cystic fibrosis. If ICSI is performed because of azoospermia due to congenital bilateral absence or atrophy of the vas deferens, the patient is offered genetic counseling to discuss testing for cystic fibrosis. (See "Cystic fibrosis: Carrier screening" and "Causes of male infertility", section on 'Sperm transport disorders'.)

PROCEDURE COMPONENTS — ICSI is a technique used during some IVF cycles to inject a single spermatozoa into an oocyte for purposes of fertilization [20].

Sperm retrieval — Sperm are typically retrieved from ejaculated semen. For individuals who are unable to ejaculate semen, there is insufficient evidence to recommend any one sperm retrieval technique over another [21]. Surgical retrieval of spermatozoa from the testicles or reproductive tract in combination with ICSI is an effective treatment for men with obstructive or nonobstructive azoospermia, ejaculatory dysfunction, or complications from cancer treatment [22]. Surgical retrieval of spermatozoa can be achieved using microsurgical epididymal sperm aspiration (MESA), percutaneous epididymal sperm aspiration (PESA), testicular biopsy (testicular sperm extraction [TESE]), or fine-needle aspiration [22-24].

●Obstructive azoospermia – For individuals with obstructive azoospermia, there is insufficient evidence to recommend any one sperm retrieval technique over another [21]. The fertilization, pregnancy, and live birth rates are equivalent with testicular or epididymal sperm retrieval for these patients [25]; however, epididymal aspiration is preferred, when possible, because of a lower risk of complications [26].

●Nonobstructive azoospermia – TESE has been successful in obtaining sperm from patients with nonobstructive azoospermia, including patients with Klinefelter syndrome, spermatogenic arrest, or Sertoli cell-only syndrome [23,27,28]. Sperm retrieval rates are higher in Klinefelter syndrome patients with serum testosterone near the reference range (>250 ng/dL) [29]. Repeated surgical retrieval of spermatozoa can be avoided by standard cryopreservation if sufficient numbers of spermatozoa are obtained [22,30]. The fertilization rate after ICSI with testicular spermatozoa in nonobstructive azoospermia is significantly lower than in obstructive azoospermia, but pregnancy and embryo implantation rates appear to be similar [31-33].

●Sperm retrieval after vasectomy – The clinical pregnancy rate of the partners of vasectomized men who have undergone TESE followed by ICSI appears to be reduced relative to men with obstructive azoospermia from other etiologies (9 versus 28 percent) [34]. This reduction in pregnancy rate was observed when the vasectomy occurred ≥10 years prior to sperm retrieval and may be related to poorer sperm quality remote from vasectomy [34-36]. The quality of post-vasectomy sperm may be compromised such that they are less capable of achieving a pregnancy.

●Use of fresh versus cryopreserved testicular sperm – In a 2014 meta-analysis of comparative studies of ICSI in men with azoospermia due to spermatogenic dysfunction, there was no statistical difference between the use of fresh versus cryopreserved-thawed testicular sperm in fertilization or clinical pregnancy rates [37].

Spermatozoa selection

Summary — All sperm samples are processed prior to ICSI. The most common type of processing entails a density gradient and centrifugation. Spermatozoa preparation skills and the ability to select a normal, viable spermatozoa for injection are important factors in the success of ICSI. They play a key role because the direct injection of spermatozoa into the oocyte bypasses natural selection, thus it could inadvertently introduce a defective paternal genome [38]. If the spermatozoa used for ICSI have outwardly normal morphology and motility, it is likely that fertilization and subsequent embryo development will occur.

Motility — Impaired motility is the semen parameter most associated with a reduction in both ICSI fertilization rates [39] and growth of good-quality embryos [40-43]. Since the human embryo derives its centriolar apparatus and mitotic potential from the spermatozoa, the use of spermatozoa with a damaged or abnormal centriole could result in embryos with severe cleavage arrest or irregular cleavage patterns. Immotile spermatozoa and poorly motile spermatozoa with no forward progression are more likely to have defective centrosomes [44,45].

Recovery of spermatozoa from density gradients [46] and treatment with 2-deoxyadenosine and/or pentoxifylline to stimulate spermatozoa motility have been used to identify live spermatozoa in semen with variable motility [4,47]. If spermatozoa remain immotile after treatment and processing, a hypoosmotic swelling test can be used as a means to select viable spermatozoa from an immobile population at the time of ICSI [48,49].

Advanced sperm selection techniques — Advanced techniques for spermatozoa selection may enhance embryo survival and pregnancy outcome for patients in whom ICSI with unselected sperm injection has failed. Spermatozoa with high levels of DNA damage may be associated with fertilization impairment and failure of embryo development after ICSI [50-52].

●Sperm DNA fragmentation – The data on the impact of sperm DNA fragmentation on clinical outcomes are controversial [53-55]. Spermatozoa that are recovered after density gradient processing have mixed DNA fragmentation levels [56] while those recovered after microfluidic processing of sperm have decreased DNA fragmentation [57,58]. More studies are needed to determine if alternatives to density gradient processing, including microfluidics, improve clinical outcomes.

●Magnetic-activated cell sorting – Magnetic-activated cell sorting (MACS) processing is another selection method that separates apoptotic from nonapoptotic sperm; preliminary studies have suggested this technique may improve embryo quality [59].

Physiologic, hyaluronan-selected intracytoplasmic sperm injection (PICSI) — Historically, embryologists selected sperm by choosing the most morphologically normal looking sperm by light microscopy or by nuclear features detected by specialized microscopy [60]. Physiologic, hyaluronan-selected intracytoplasmic sperm injection (PICSI) is a sperm isolation procedure where the processed sperm is placed over hyaluronan prior to ICSI. The selection of sperm for ICSI by the hyaluronic acid binding method is based on the ability of competent mature sperm to attach themselves to hyaluronic acid through specific receptors found on the sperm plasma membrane. Sperm with diminished maturity, increased levels of chromosomal aberrations, or failed spermatogenetic membrane remodeling will not bind to hyaluronic acid. The selection of sperm bound to hyaluronic acid for ICSI may facilitate the selection of individual mature sperm with low levels of chromosomal aneuploidies and thus be associated with lower rates of miscarriage after ICSI [61].

In a 2019 meta-analysis of trials comparing advanced sperm selection techniques, miscarriage risk was lower for patients undergoing ICSI with hyaluronic acid-selected sperm (ICSI-HA, or PICSI) versus ICSI alone (3 to 6 percent for ICSI-HA versus 7 percent with ICSI alone, risk ratio [RR] 0.61, 95% CI 0.45-0.83, 3005 women), but live birth rates were similar between the groups (RR 1.09, 95% CI 0.97-1.23, 2903 women) [62].

Oocytes — Oocytes are obtained from a female in the same manner as in conventional IVF procedures (see "In vitro fertilization: Overview of clinical issues and questions").

●Impact of maternal factors on outcomes – Several studies have suggested that factors such as maternal age and oocyte quality and quantity have a greater impact upon ICSI success than the severity of semen abnormalities [42,63,64]. Oocytes derived from poor-quality stimulations (poor responders, hyper-responders) or exhibiting cytoplasmic abnormalities demonstrate higher rates of degeneration, abnormal fertilization, and pregnancy loss [65-67].

●Oocyte preparation – The oocytes are denuded of cumulus-coronal cells by exposure to hyaluronidase, and residual cells are gently aspirated with a finely pulled pipette. Excessive exposure to hyaluronidase or aggressive manipulation of oocytes to remove cells may parthenogenetically activate oocytes or reposition the first polar body [68-70].

●Oocyte selection – The oocytes are graded morphologically and only oocytes at metaphase II exhibiting a distinct extruded first polar body are used for injection.

Laboratory — Laboratory protocols and procedures should protect gametes from temperature and pH variations and fluctuations, which may disrupt spindles and contribute to abnormal chromosome distribution [71]. One example of semen processing guidelines can be found through the World Health Organization (WHO) [72].

●Embryologist – The technique for ICSI involves the use of sophisticated instruments and requires a trained embryologist [73].

●Microscope – An inverted microscope with high-quality optics (eg, Nomarski or Hoffman) should be used for the most accurate visualization of gametes and microtools, thereby decreasing oocyte damage while optimizing fertilization rates.

•Setup and tools – The inverted microscope should be located on an antivibration table in a quiet area of the laboratory and be fitted with at least a stage warmer, high-precision micromanipulators, and microsyringe injection systems operated hydraulically by air or oil [74-76]. Micromanipulators offer the capability to manipulate gametes with precise movements at microscopic levels. Fabrication of microtools requires a microforge, pipette puller, and microgrinder, although most laboratories purchase high-quality precision ready-made microtools from manufacturers.

•Polarization microscopy – A sophisticated heated optical system, such as polarization microscopy, can be used to monitor spindle position during injection and reduce spindle damage during the ICSI procedure [71,77,78]. However, more studies are needed to determine whether polarization microscopy improves clinical outcomes, particularly live birth rate.

•Intracytoplasmic morphologically selected sperm injection (IMSI) – IMSI is a variation of ICSI that uses a higher-powered microscope lens to select sperm. This allows the embryologist to assess sperm in greater detail. Some studies suggest that this technique selects better quality sperm and results in higher implantation rates and lower miscarriage rates when compared with traditional ICSI [79]. However, data supporting IMSI are limited, and IMSI has not replaced ICSI for routine use [80,81].

Fertilization — Fertilization rates vary by indication (male factor or non-male factor) and technique but generally fall in the 50 to 80 percent range [82,83].

Spermatozoon injection — An injection pipette containing an immobilized spermatozoon is gently pushed through the zona pellucida and through the oolemma into the center of the oocyte. The spermatozoa should be delivered with the smallest possible amount of medium. Negative pressure is then used to break the oolemma, followed by gentle aspiration of the cytoplasm. Whether or not different methods of depositing sperm, breaking the oolemma, and aspirating cytoplasm for oocyte activation impact fertilization and embryo development rates are an active area of investigation [70,84-86].

●Laser-assisted ICSI – Laser-assisted ICSI is an innovative approach that has been used in patients with a history of poor ICSI outcome and with limited metaphase II oocytes. This technique is less traumatic to the oocytes during the ICSI procedure and has resulted in improved fertilization rates and embryo quality [87].

●Piezo-driven pipettes – ICSI injection technology using piezo-driven pipettes has been successfully applied in a number of mammalian species [88,89]. Damage to the oocyte is greatly reduced because the injector uses ultrasonic cutting forces, rather than piercing forces, to penetrate the oolemma, thus there is almost no deformation of the oocyte during the injection. This technique results in comparably high survival and success rates [90-92].

After injection, the oocytes are cultured according to standard laboratory protocols.

Fertilization rates — The fertilization rate following ICSI is approximately 50 to 80 percent [82,83]. Although ICSI does not guarantee fertilization, the incidence of complete fertilization failure is low and usually occurs in cycles with low oocyte yield [41].

ICIS fertilization rates are impacted by the following:

●Failure of fertilization – Failure of fertilization is typically not due to nonplacement or ejection of the spermatozoa from the oocyte [85,86,93,94]. It may be caused by the failure of the oocytes to undergo activation, which is usually related to poor oocyte quality or sperm nonviability. Cytoplasmic maturation and fertilization rates can be enhanced by extending the oocyte preincubation time after retrieval and prior to ICSI [95], by assisted oocyte activation [96-98], and by avoiding use of fresh ejaculates with globozoospermia [99] or no motility [40], and testicular sperm with no or partial motility.

●Oocyte degeneration – The incidence of oocyte degeneration after ICSI may be as high as 8 to 20 percent of procedures. The etiology may be due to manipulation and/or inherent in the oocyte quality. Each laboratory should analyze their rate to determine if technical or stimulation problems exist [65-67,86].

●Laboratory – ICSI outcomes are also highly dependent upon the technical expertise of the embryologist [86].

Assessment of fertilization — Any abnormally fertilized oocyte derived from ICSI should be discarded and not considered for embryo transfer.

●Pronuclear formation – Assessment of pronuclear formation after ICSI is necessary to distinguish and separate abnormally fertilized oocytes from normally fertilized oocytes, which possess two pronuclei, male and female, and extruded first and second polar bodies.

•Timing of assessment – Timing of pronuclear assessment may need to be altered since pronuclear formation may be advanced in ICSI fertilized oocytes [100,101].

•Polyspermia – Polyspermia should not be an issue since only one spermatozoon is introduced into the oocyte during injection.

●Abnormal pronuclei – Monospermic digynic (tripronuclear) and single pronucleate oocytes may occur more frequently with ICSI. For this reason, verification of the number of polar bodies at the time of fertilization assessment is essential. Tripronuclear oocytes with one polar body result from the nonextrusion of the second polar body and may be a consequence of damage or disruption to the spindle [70,77,102,103]. Pronuclear oocytes are not the result of asynchronous pronuclear development, but rather a failure of sperm to decondense fully and form the male pronucleus [104].

Embryo formation and selection — Male factor infertility may reduce blastocyst production but supporting data are limited [105-111]; any potential difference does not appear to have a significant clinical impact [112].

Embryo selection following ICSI is to the same as for conventional IVF. (See "In vitro fertilization: Procedure", section on 'Embryo selection'.)

Embryo cryopreservation — Additional embryos can be cryopreserved for use in future IVF cycles.

●(See "Fertility preservation: Cryopreservation options", section on 'Embryo'.)

●(See "In vitro fertilization: Procedure", section on 'Cryopreservation'.)

PREIMPLANTATION AND PREGNANCY GENETIC TESTING — Use of preimplantation genetic testing (PGT) or prenatal screening for aneuploidy is based on patient preferences and the clinical scenario; use of ICSI alone is not an indication for either. Patients considering ICSI should be informed of the risk of an abnormal fetal karyotype due to paternally inherited chromosomal abnormalities, the relatively benign phenotype of some of these chromosomal anomalies, and the risks associated with invasive prenatal diagnostic procedures so that they may make an informed choice about prenatal testing. (See "Preimplantation genetic testing".)

OUTCOMES — ICSI outcome can be viewed in terms of pregnancy rate and complications, neonatal status, and long-term physical and developmental issues. Potential risks accrue from iatrogenic, rather than natural, selection of the oocyte and sperm and technical concerns relating to the procedure itself (eg, injection of contaminants, disruption of the ooplasm, dysregulation of normal genetic processes).

A discussion of pregnancy, maternal, and child outcomes after assisted reproductive technology, including ICSI, is presented separately.

●(See "Assisted reproductive technology: Pregnancy and maternal outcomes".)

●(See "Assisted reproductive technology: Infant and child outcomes".)

Pregnancy — The following data are specific to pregnancies conceived with ICSI:

●Live birth rate – In well-established centers, 30 percent of all IVF cycles (combined maternal age groups) result in a live birth [83,113], irrespective of sperm origin or count [114,115]. ICSI outcomes do not differ substantially from those of conventional IVF cycles [116,117].

●Monochorionic twin gestation – ICSI appears to increase the risk of monochorionic placentation, particularly when combined with blastocyst transfer [118-120]. Moreover, there are two case reports of dizygotic twins with monochorionic placentation; both involved ICSI [121,122]. The mechanism has not been explained, but may have been related to the procedure. The splitting of the inner cell mass caused by the artificial opening induced by the ICSI procedure has been proposed as a mechanism.

●Pregnancy and maternal outcomes – An in-depth discussion of the outcome of pregnancies conceived through IVF with or without ICSI as well as maternal outcomes can be found separately (see "Assisted reproductive technology: Pregnancy and maternal outcomes"). Selected issues specific to ICSI are discussed below.

Pediatric issues

Overall outcome — Children conceived via ICSI have been followed for up to 22 years [123]. Psychological outcomes, pubertal staging, neurological examination, cognitive development, and rates of surgery/hospitalization/remedial therapy were similar for ICSI children and those conceived spontaneously at up to age 11 years [124-126]. Physical and developmental health at age 5.5 years of age appeared to be comparable to that of naturally conceived children [127,128].

●(See "Assisted reproductive technology: Infant and child outcomes".)

●(See "Assisted reproductive technology: Pregnancy and maternal outcomes".)

Genetic alterations and congenital anomalies — The ICSI procedure itself and use of sperm from subfertile males may somewhat increase the risk of chromosomal anomalies or imprinting disorders in the offspring. The risk of congenital anomalies with ICSI is similar to IVF and slightly increased compared with natural conception [129]. The increased risk of genetic alterations from ICSI is much lower than the risk of receiving a chromosomal abnormality from the oocyte and thus does not significantly alter the clinical outcome, other than possible increased risk of infertility, in the offspring.

●Chromosomal abnormalities – Both the ICSI procedure itself and using sperm from subfertile men may increase the potential to transmit genetic or chromosomal abnormalities to offspring created from ICSI technology [130-133]. These concerns have been validated as both de novo sex and autosomal chromosome aberrations appear to increase after ICSI. (See "Assisted reproductive technology: Infant and child outcomes", section on 'Chromosomal and genetic alterations'.)

Subfertile individuals are more likely than fertile individuals to have chromosomal abnormalities (eg, aneuploidies, structural abnormalities, gene mutations, microdeletions) that may contribute to their subfertility and may be passed to their offspring [18,134-137]. These abnormalities may be confined to the sperm or they may be autosomal [138]. One study that performed prenatal diagnosis on 1586 fetuses conceived with ICSI reported 25 de novo chromosomal abnormalities (10 of the sex chromosome, 15 autosomal) and 22 inherited chromosomal abnormalities (mean maternal age was 33.5 years) [139]. This represented a significantly increased rate of de novo chromosomal anomalies in ICSI offspring (1.6 versus 0.5 percent in controls), and was related mainly to a higher number of sex chromosomal anomalies and partly to a higher number of autosomal structural anomalies. In addition, 17 of the 22 inherited chromosomal anomalies were paternally derived [140]. (See 'Pretreatment evaluation and counseling' above and "Causes of male infertility".)

●Imprinting disorders – There is a possibility that ICSI interferes with genomic imprinting during germ cell development and preimplantation [130,141,142]. In reports describing three cases of Angelman syndrome after ICSI, epigenetic defects were detected with loss of methylation of the maternal allele [143,144]. However, the baseline risk of an imprinting disorder such as Angelman syndrome is low (less than 1 in 100,000), so any small increase in risk still results in only rare occurrences of the disorder. (See "Assisted reproductive technology: Infant and child outcomes", section on 'Imprinting disorders'.)

●Congenital anomalies – There is a small increase in risk of major malformations in ICSI conceived children compared with those conceived by IVF alone or spontaneously conceived [115,124,145-150]. The best documented concern is for an increased risk of hypospadias and imprinting disorders, but the evidence is still inadequate to conclude that such a relationship exists. Both study and control children should be examined in the same way and at the same age by blinded examiners using the same definitions of major/minor birth defects and the data should be corrected for confounders, such as maternal age, plurality, and chromosomal abnormalities.

Further discussion of congenital anomalies in offspring conceived with assisted reproductive technology is presented in related content. (See "Assisted reproductive technology: Infant and child outcomes", section on 'Congenital anomalies'.)

Risk of cystic fibrosis — Several cystic fibrosis mutations are consistently associated with congenital absence of the vas deferens (ΔF508, R1 17H, 5Tvar, 7Tvar), which is one indication for ICSI. If ICSI is performed because of azoospermia due to congenital bilateral absence or atrophy of the vas deferens, the couple should be offered genetic counseling to discuss testing for cystic fibrosis [151].

●(See 'Pretreatment evaluation and counseling' above.)

●(See "Cystic fibrosis: Carrier screening".)

Male-to-female sex ratio at birth — Use of ICSI appears to impact the sex ratio at birth when compared with conventional IVF and may in part be further impacted by the route for obtaining sperm (ejaculated versus nonejaculated) [152]. The percent of male infants is approximately one to two percent lower after ICSI than after IVF and varies with geographic location of the study [153-155]. This has been hypothesized to be due to the higher proportion of male infertility among ICSI patients and to iatrogenic factors related to ICSI, both of which might lead to fewer males in ICSI conceived pregnancies. A higher male-to-female ratio after blastocyst transfer than after cleavage-stage transfer has also been observed [153-156]. Since embryos are selected for transfer on the basis of the degree of cleavage in addition to morphological evaluation, one theory is that male embryos divide faster.

Reproductive function — Data regarding postpubertal reproductive endocrine function are limited but generally reassuring.

●Female offspring – In the study with the longest follow-up comparing women aged 18 to 22 years conceived with ICSI versus those conceived spontaneously, there were no differences in reproductive hormone levels (antimüllerian hormone [AMH], follicle-stimulating hormone [FSH], luteinizing hormone [LH], and dehydroepiandrosterone sulfate [DHEAS]) between the groups [123]. In addition, the mean follicle count and the proportion of women with >19 follicles per ovary (approximately 20 percent of women) were the same. While data demonstrating the ability of these women to conceive and deliver a live-born child are not yet available, the current information is reassuring regarding normal reproductive hormone development.

●Male offspring – For men conceived by ICSI, reproductive hormone development, including FSH, LH, testosterone, and inhibin B, also appears to be similar to spontaneously conceived men [157]. However, semen analysis parameters appear to differ. In a study of men aged 18 to 22 years old who were conceived by ICSI because of male factor infertility, the ICSI-conceived men had lower sperm concentration and twofold lower total sperm counts and total motile counts after adjusting for confounders [158]. In addition, the ICSI-conceived men were more likely to have sperm concentration and total sperm counts below the World Health Organization (WHO) reference values. Limitations of this study include small sample size, the availability of only one semen specimen per individual, and lack of generalizability to ICSI done for other indications. Whether or not these altered semen parameters will impact the individual's ability to father a child is not yet known.

RESOURCES FOR PATIENTS AND CLINICIANS

●US Centers for Disease Control and Prevention Key Findings: Use of Intracytoplasmic Sperm Injection (ICSI) in the United States

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Female infertility" and "Society guideline links: Male infertility or hypogonadism".)

SUMMARY AND RECOMMENDATIONS

●Indications – Intracytoplasmic sperm injection (ICSI) is a technique used during some in vitro fertilization (IVF) cycles to inject a single spermatozoa into an oocyte for purposes of fertilization. The technique is primarily used for treatment of male factor infertility and for treatment of couples with lower than expected or failed fertilization with conventional insemination in a prior IVF cycle. (See 'Indications' above.)

●Pretreatment evaluation – Individuals considering ICSI for significant male factor infertility first undergo a comprehensive evaluation. We suggest offering men with azoospermia or severe oligozoospermia screening for chromosomal abnormalities, including Y chromosome microdeletions. If ICSI is performed because of azoospermia due to congenital bilateral absence or atrophy of the vas deferens, the couple should be offered genetic counseling to discuss testing for cystic fibrosis. (See 'Pretreatment evaluation and counseling' above.)

●ICSI procedure – ICSI involves the injection of a single sperm into an oocyte for purposes of fertilization. Steps include sperm retrieval (ejaculated or surgical), spermatozoa selection, oocyte retrieval, oocyte fertilization, embryo selection for transfer, and storage of additional embryos.  

●Live birth rate – In well-established centers, 30 percent of all IVF cycles result in a live birth, irrespective of sperm origin or count. ICSI outcomes do not differ substantially from those of conventional IVF cycles. (See 'Pregnancy' above.)

●Child outcome – Children born from ICSI appear to have similar psychological outcomes, pubertal staging, neurological examination, cognitive development, and rates of surgery/hospitalization/remedial therapy to those conceived spontaneously. Risks of specific genetic alterations may be increased in some cases. (See 'Pediatric issues' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff thank Dr. Kathleen Miller for her past contributions as an author to prior versions of this topic review.