ICSI treatment (Intracytoplasmic Sperm Injection) is a specialised fertilisation technique used as part of an IVF cycle. During ICSI, a skilled embryologist selects a single sperm and injects it directly into a mature egg in the laboratory, helping to overcome certain difficulties that may prevent fertilisation from occurring naturally or with conventional IVF.
ICSI is most commonly recommended in cases of male infertility, such as a very low sperm count, reduced sperm motility or abnormal sperm morphology. It may also be considered when previous IVF treatment has resulted in poor or failed fertilisation, or when sperm has been obtained through surgical sperm retrieval.
The stages leading up to ICSI are similar to standard IVF, including ovarian stimulation and egg retrieval. The main difference is the way fertilisation takes place in the laboratory. By introducing a single sperm directly into the egg, ICSI bypasses several of the natural barriers to fertilisation.
The decision to use ICSI is made after assessing the couple’s fertility history, semen parameters and previous treatment outcomes, so that the most appropriate fertilisation method can be selected.
The main difference between IVF and ICSI therefore lies in how fertilisation takes place in the laboratory. In standard IVF, sperm are placed together with the eggs, whereas during ICSI a single sperm is individually injected into each suitable mature egg.
Who May Be Recommended ICSI?
ICSI may be recommended when there is a specific factor that could make conventional fertilisation more difficult. It is particularly useful in cases of male infertility, where the number, movement or quality of sperm may reduce the chances of a sperm successfully entering and fertilising an egg.
ICSI may be considered in cases such as:
- Very low sperm count.
- Poor sperm motility.
- Abnormal sperm morphology.
- Previous IVF treatment in which very few or none of the eggs fertilised.
- Sperm obtained through surgical sperm retrieval from the testicle or epididymis.
- Selected cases where frozen sperm of limited quality is being used.
These are among the recognised indications for ICSI described by the Human Fertilisation and Embryology Authority.
ICSI and Male Infertility
ICSI has significantly expanded the treatment options available to men with severe male-factor infertility. Because a single sperm is injected directly into a mature egg, the technique can bypass some of the difficulties associated with low sperm numbers, reduced motility or problems with sperm morphology.
However, ICSI is not automatically more appropriate than conventional IVF for every couple. When there is no clear sperm-related indication, current guidance does not show a clear benefit from routinely using ICSI instead of standard IVF.
The decision is therefore made individually after evaluating the semen analysis, fertility history and any previous assisted reproduction treatment.
How Is ICSI Performed?
ICSI is performed as part of an IVF cycle, so the stages leading up to fertilisation are largely the same as those used in conventional IVF. The main difference occurs in the laboratory, where a single sperm is injected directly into a mature egg rather than sperm and eggs simply being placed together.
The main stages include:
1. Ovarian stimulation
Hormonal medication is used to stimulate the ovaries so that several eggs can develop during the treatment cycle.
2. Egg retrieval
Once the eggs are ready, they are collected from the ovaries and examined in the laboratory to identify those that are mature and suitable for ICSI.
3. Sperm preparation and selection
A sperm sample is prepared, and an embryologist selects an appropriate individual sperm for injection.
4. Injection of the sperm into the egg
Using specialised laboratory equipment and a microscope, the embryologist carefully injects a single sperm directly into the cytoplasm of a mature egg.
5. Fertilisation and embryo development
After ICSI, the eggs are cultured in the laboratory and checked for signs of fertilisation. Successfully fertilised eggs are then monitored as they develop into embryos.
The subsequent stages, including embryo culture and embryo transfer, follow the same general process as a conventional IVF cycle.
ICSI vs IVF – What Is the Difference?
ICSI and conventional IVF follow many of the same treatment stages. In both methods, the ovaries are stimulated with medication, the eggs are collected and fertilisation takes place in the laboratory. The main difference between ICSI and IVF is the way the sperm fertilises the egg.
In conventional IVF, a prepared sperm sample is placed together with the eggs in a laboratory dish. Fertilisation then occurs when a sperm successfully enters an egg.
With ICSI, an embryologist selects a single sperm and injects it directly into the cytoplasm of a mature egg using specialised laboratory equipment. This allows some of the natural barriers to fertilisation to be bypassed.
ICSI is therefore often considered when there is a significant male fertility factor, when sperm has been obtained surgically or when previous conventional IVF has resulted in poor or failed fertilisation. Conventional IVF may remain appropriate when there is no specific reason to use ICSI. (hfea.gov.uk)
After fertilisation, both treatments follow a similar pathway. The embryos are cultured and monitored in the laboratory, and a suitable embryo may then be selected for transfer to the uterus.
The choice between IVF and ICSI depends on the couple’s individual fertility assessment and treatment history.
ICSI and Surgical Sperm Retrieval
ICSI can also provide a treatment option for men who have no sperm or extremely low numbers of sperm in the ejaculate. In selected cases, sperm may be retrieved directly from the epididymis or testicle and then used to fertilise the woman’s eggs through ICSI.
Surgical sperm retrieval may be considered in cases of obstructive azoospermia, where sperm production may be present but a blockage prevents sperm from reaching the ejaculate. It may also be used in selected cases of non-obstructive azoospermia, where sperm production itself is significantly reduced.
Depending on the individual diagnosis, different sperm retrieval techniques may be considered, including:
- PESA – Percutaneous Epididymal Sperm Aspiration
- MESA – Microsurgical Epididymal Sperm Aspiration
- TESA – Testicular Sperm Aspiration
- TESE – Testicular Sperm Extraction
- MicroTESE – Microscopic Testicular Sperm Extraction
When viable sperm are successfully retrieved, they can be used with ICSI because only a single suitable sperm is required for injection into each mature egg.
The most appropriate sperm retrieval technique depends on the underlying cause of infertility and should be determined after specialist evaluation. Successful sperm retrieval does not guarantee fertilisation, pregnancy or live birth, as the overall outcome also depends on several other fertility-related factors.
ICSI Success Rates and What Affects the Outcome
ICSI is highly effective as a laboratory technique for helping sperm fertilise an egg, particularly when male-factor infertility is present. However, successful fertilisation is only one stage of fertility treatment and does not necessarily mean that pregnancy or live birth will follow.
The overall success of an ICSI cycle depends on several individual factors, including:
- The woman’s age.
- The number and quality of mature eggs collected.
- Sperm quality and the underlying cause of male infertility.
- The ability of fertilised eggs to develop into good-quality embryos.
- The health of the uterus and endometrium.
- Other fertility conditions affecting either partner.
For this reason, there is no single ICSI success rate that applies to every patient. According to the HFEA, pregnancy outcomes following ICSI tend to be similar to those seen with conventional IVF, and separate success-rate statistics are therefore not routinely published for the two fertilisation methods.
ICSI should primarily be viewed as a technique designed to improve the opportunity for fertilisation when there is a specific indication. It does not guarantee that every injected egg will fertilise or that every resulting embryo will lead to pregnancy.
An individual assessment of age, ovarian reserve, sperm parameters and previous fertility treatment provides a more meaningful indication of the expected chances of success.
Frequently Asked Questions About ICSI
What is ICSI in IVF?
ICSI, or Intracytoplasmic Sperm Injection, is a fertilisation technique used within an IVF cycle. A single sperm is selected by an embryologist and injected directly into a mature egg to assist fertilisation.
What is the difference between IVF and ICSI?
The main difference is how fertilisation takes place. In conventional IVF, eggs and sperm are placed together in the laboratory. With ICSI, one sperm is injected directly into each suitable mature egg. The remaining stages of treatment are generally similar.
When is ICSI recommended?
ICSI may be recommended when there is a very low sperm count, poor sperm motility or morphology, previous poor or failed fertilisation with IVF, or when sperm has been obtained through surgical retrieval.
Can ICSI be used for severe male infertility?
Yes. ICSI is commonly used in cases of significant male-factor infertility. It may also be combined with surgical sperm retrieval when sperm are absent or present in extremely low numbers in the ejaculate.
Does ICSI guarantee fertilisation or pregnancy?
No. ICSI helps overcome certain barriers to fertilisation, but it cannot guarantee that every egg will fertilise or that treatment will result in pregnancy. Outcomes also depend on factors such as the woman’s age, egg quality, sperm characteristics and embryo development.
