Intracytoplasmic Sperm Injection (ICSI) 2025: indications, process, evidence, risks & how it differs from IVF

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Zappelphilipp Marx•
ICSI in a laboratory: a single sperm cell is injected through a fine capillary directly into the egg

Intracytoplasmic sperm injection (ICSI) is a laboratory technique in assisted reproduction where a single sperm is injected directly into a mature egg. This guide offers a concise, evidence-led overview without hype: clear indications, realistic success factors, the workflow, safety considerations, the role of lab options, and a balanced comparison with IVF, IUI and ICI.

What is ICSI?

Unlike conventional IVF, where eggs are incubated with many sperm, ICSI uses a microneedle to place one viable sperm into the egg’s cytoplasm. This can bypass barriers in cases of marked semen abnormalities or after prior fertilisation failure. A patient-friendly introduction is available from the UK regulator: HFEA: ICSI.

Who is ICSI for?

Typical indications include:

  • Significant male factor (clearly reduced concentration, motility or morphology; antisperm antibodies).
  • Fertilisation failure in a previous IVF cycle.
  • Use of surgically retrieved sperm (PESA/MESA/TESE/mTESE).
  • Very few mature eggs on retrieval day when optimising fertilisation is prudent.

Professional societies also note: when there is no male factor, ICSI usually offers no added benefit over conventional IVF; routine use is not recommended. See for example the committee opinion: ASRM.

Evidence and success rates

Live-birth chances are driven primarily by age and egg quality, not by choosing ICSI per se. With a clear male factor, ICSI often achieves high fertilisation rates; without it, systematic comparisons show no consistent advantage for clinical outcomes (pregnancy or live birth) over IVF. See the overview: Cochrane.

Step-by-step process

  • Preparation: history, investigations, infection screening; counselling on alternatives, chances and risks.
  • Stimulation & monitoring: ovarian stimulation with ultrasound and hormone checks; OHSS prevention.
  • Egg collection: ultrasound-guided follicle aspiration to collect mature oocytes.
  • Semen preparation: collection and processing; surgical retrieval if needed (e.g., TESE).
  • ICSI: selection of motile sperm and micro-injection into each mature egg.
  • Embryo culture: monitoring development, often to the blastocyst stage.
  • Embryo transfer: transfer of a single suitable embryo (single-embryo transfer preferred); remaining embryos may be frozen.
  • Luteal phase & test: progesterone support; pregnancy test about 10–14 days after transfer.

For a readable comparison of IVF versus ICSI, see NHS Inform.

Risks and safety

Key risks relate to stimulation (e.g., OHSS), procedures (rare bleeding/infection) and multiple pregnancy if more than one embryo is transferred. Micromanipulation can mechanically damage some eggs; reputable patient information is transparent about this (e.g., NHS patient leaflet). Overall, long-term data are reassuring; small risk increases can be hard to separate from effects of the underlying infertility.

Lab options (“add-ons”)

Many add-ons (e.g., PICSI/IMSI, certain culture supplements) do not reliably increase live-birth rates for most patients. The HFEA grades add-ons using a transparent “traffic-light” system and advises caution without a clear indication: HFEA Add-ons.

Comparison: ICI · IUI · IVF · ICSI

CriterionICIIUIIVFICSI
PrinciplePlace sample near the cervixWashed sperm into the uterusEgg + many sperm in the labOne sperm injected into the egg
Typical indicationEntry option without major factorsUnexplained infertility, mild male factor, donor spermTubal factor, endometriosis, failed IUIMarked male factor, fertilisation failure
Per-cycle successRather low; timing mattersModerate; higher with stimulationHigher than IUI; age-dependentSimilar to IVF; advantage mainly with male factor
ComplexityLowLow–moderateModerate–high (laboratory)High (micromanipulation)
Main risksLow; hygiene is keyMultiple pregnancy risk with stimulationOHSS, procedural risks, multiplesAs in IVF + potential egg damage

Takeaway: use ICSI selectively when a clear benefit is expected; without male factor, conventional IVF remains standard (see the Cochrane analysis above).

Planning, timing and practical tips

  • Define the indication precisely (male factor, prior fertilisation failure, special findings).
  • Discuss prognosis realistically: outcomes are dominated by age and egg quality.
  • Prefer single-embryo transfer; actively avoid multiple pregnancy.
  • Prevent OHSS: measured stimulation, an appropriate trigger strategy, and consider “freeze-all” if at risk.
  • Scrutinise add-ons and use only with a plausible indication/evidence (refer to HFEA ratings).

RattleStork – be better prepared for ICSI decisions

RattleStork isn’t a clinic and doesn’t replace medical advice. It helps with structure and communication: verified profiles, secure messaging, and private notes and checklists for appointments, medicines and questions for your care team. Keep everything in one place — from the first consult to embryo transfer.

RattleStork app with verified profiles, secure chat and private notes to plan ICSI
RattleStork: find community, organise information, and make ICSI decisions feeling prepared.

Conclusion

ICSI is a precise lab technique with clear value for significant male-factor infertility or after fertilisation failure. Without male factor, it usually adds no benefit over conventional IVF. Good practice means: clear indication, realistic expectations, cautious stimulation, a conservative embryo number and a critical view of add-ons.

Disclaimer: Content on RattleStork is provided for general informational and educational purposes only. It does not constitute medical, legal, or other professional advice; no specific outcome is guaranteed. Use of this information is at your own risk. See our full Disclaimer.

Frequently Asked Questions (FAQ)

With ICI, a semen sample is placed in the posterior vaginal fornix near the cervix so sperm can travel on their own through the cervix, uterus and fallopian tubes to the egg; fertilisation and implantation occur in the body and the technical set-up is simple.

ICI places an essentially unprocessed sample in front of the cervix, whereas IUI uses a washed, concentrated sample delivered by catheter directly into the uterus, which often improves success but requires a clinical setting.

In practice, ranges of about five to fifteen per cent per cycle are often cited, driven mainly by age, cause of infertility, sample quality, cycle regularity and precise timing; several well-planned attempts are common before considering other methods.

Ideally very close to ovulation; insemination often occurs on the day of a positive LH test and may be repeated the next day, with ultrasound-guided cycle monitoring offering the most precise planning.

Most people find ICI brief and well tolerated; with clean technique, meaningful risks are low, but pain, fever, unusual discharge or bleeding should be assessed by a clinician to rule out infection or other causes.

Typically a sterile collection cup, a single-use needle-free syringe and a clean surface, with optional disposable gloves; use sperm-friendly materials without toxic additives and dispose of single-use items properly after one use.

Yes. After ejaculation, wait for liquefaction so the sample is less viscous; avoid heat or cold extremes, since temperature swings can impair motility.

If needed, use a small amount of a product labelled sperm-friendly, as many common gels reduce motility; avoid contact between the sample and unsuitable substances.

Many lie quietly for a few minutes after placing the sample to limit backflow; proven benefits beyond this short rest are uncertain, and light daily activities are usually fine afterwards.

After several well-timed cycles without success, an interim medical review is often recommended; depending on age, findings and semen quality, moving to IUI or IVF/ICSI may better target higher chances.

Yes; standardised screening and documentation, clear consents and secure sourcing are essential, since sample quality and traceability are central to safety and success.

Tubal blockage, marked male factor, very irregular cycles or multiple well-timed but unsuccessful attempts make ICI less promising; IUI or IVF/ICSI are usually better options in such cases.

An interval of roughly two to three days is often suggested to balance concentration and motility; very short or very long intervals can reduce sample quality.

Up-to-date screening for transmissible infections is important, especially with donor sperm or a new partner; medical assessment is also advisable for cycle irregularity, pain, suspected endometriosis or recurrent miscarriage.