ICSI, or Intracytoplasmic Sperm Injection, is a specialized form of in vitro fertilization (IVF) designed to overcome certain infertility challenges. This advanced reproductive technology involves the precise injection of a single sperm directly into a mature egg. The procedure aims to achieve fertilization when natural sperm-egg interaction is unlikely or has failed. It has become a widely adopted method in reproductive medicine globally.
How ICSI Works
The ICSI process begins with ovarian stimulation, where fertility medications are administered for 8 to 12 days to encourage the ovaries to produce multiple mature eggs. These medications involve daily injections of gonadotropins, hormones that stimulate follicle growth. Regular monitoring through ultrasound scans and blood tests tracks follicle development and hormone levels.
Once the eggs are mature, an egg retrieval procedure is performed, usually under light sedation. A thin needle, guided by transvaginal ultrasound, aspirates fluid from the ovarian follicles, collecting the eggs. Simultaneously, a sperm sample is collected from the male partner, either through ejaculation or surgical retrieval from the testes or epididymis.
In the laboratory, embryologists prepare the collected sperm by washing and concentrating it to isolate motile sperm. Each mature egg is then held under a microscope using a specialized holding pipette. A single sperm is selected and drawn into a glass injection pipette.
The injection pipette is then used to pierce the outer layers of the egg, the zona pellucida and the oolemma, to deposit the sperm directly into the egg’s cytoplasm. This direct injection bypasses any barriers the sperm might encounter during natural fertilization or traditional IVF. After injection, the eggs are placed in a culture dish within an incubator, where they are monitored for signs of fertilization, indicated by the appearance of two pronuclei within 16 to 18 hours. The successfully fertilized eggs, now called zygotes, continue to develop into embryos over the next three to five days before one or more are selected for transfer into the uterus.
When ICSI is Recommended
ICSI is recommended for couples experiencing male factor infertility. This includes situations where the male partner has a low sperm count (oligozoospermia, fewer than 15 million sperm per milliliter of semen). It is also indicated for individuals with poor sperm motility (asthenozoospermia), where a low percentage of sperm exhibit progressive movement (less than 40%).
Another reason for ICSI is abnormally shaped sperm (teratozoospermia), where a high percentage of sperm have irregular forms, potentially hindering their ability to fertilize an egg naturally. For men with an inability to ejaculate sperm or blockages in their reproductive tract, sperm can be surgically retrieved directly from the epididymis or testes. In these cases, the number of retrieved sperm is limited, making ICSI beneficial as it requires only a single sperm per egg.
ICSI may also be considered for couples who have experienced previous fertilization failures with traditional IVF, even when sperm parameters appear normal. This suggests an underlying issue with sperm-egg interaction that ICSI can circumvent. The technique is also used when employing frozen sperm samples or in cases involving preimplantation genetic testing (PGT) to reduce contamination.
ICSI Versus Traditional IVF
The primary distinction between ICSI and traditional IVF lies in the method used to achieve fertilization. In traditional IVF, eggs and sperm are combined in a laboratory dish after retrieval, allowing fertilization to occur naturally, mimicking the process within the body.
Conversely, ICSI involves the direct injection of a single sperm into each mature egg, bypassing the need for the sperm to penetrate the egg’s outer layers independently. This direct intervention is advantageous when sperm have difficulty reaching or entering the egg. Both ICSI and traditional IVF share initial steps, such as ovarian stimulation to produce multiple eggs and subsequent egg retrieval.
Following fertilization, whether by traditional IVF or ICSI, the resulting embryos are cultured in the laboratory for several days. The final stage for both methods involves the transfer of selected embryos into the woman’s uterus. While the fertilization step differs significantly, the overall framework of the IVF cycle remains consistent.
Effectiveness and Considerations
The success rates of ICSI are comparable to those of traditional IVF, with outcomes varying based on factors such as the woman’s age, the cause of infertility, and embryo quality. For women under 35, the live birth rate per embryo transfer cycle can range from 40% to 60%. While ICSI addresses fertilization issues, it does not guarantee embryo development or successful implantation.
ICSI is considered more invasive than traditional IVF due to the specialized micromanipulation required for sperm injection. This complexity translates to higher costs, as it demands skilled embryologists and advanced laboratory equipment. The cost of an ICSI cycle can be several thousand dollars more than a traditional IVF cycle, depending on the clinic and circumstances.
A risk associated with ICSI is damage to the egg during injection, though this occurs in a small percentage of cases (1% to 2%). Long-term studies evaluating the health and development of children born via ICSI have not identified significant differences when compared to children conceived naturally or through standard IVF. While some research has explored minor increases in certain conditions, these findings are not clinically significant and require further investigation.