IVF vs ICSI: what is the difference and who needs which

People often ask whether to "have IVF or ICSI", as though they were two different treatments. In practice, ICSI is a variation on the fertilisation step of IVF. The NHS describes IVF as a fertility treatment in which eggs are fertilised with sperm in a laboratory and the embryo is placed in the womb. The HFEA, the UK regulator of fertility treatment, explains that ICSI is performed as part of IVF and involves sperm being injected directly into the egg.

Everything around that step is the same: medicines to stimulate the ovaries, scans, egg collection, embryo culture in the laboratory, embryo transfer and the pregnancy test. The HFEA states that treatment is exactly the same as with IVF and the only difference is that, instead of mixing the sperm with the eggs and leaving them to fertilise, an embryologist injects a single sperm into each egg.

The NHS says a full cycle of IVF takes around 3 to 6 weeks and usually follows six steps: medicine to suppress the ovaries' natural egg production, medicine to increase the egg supply with scans to monitor it, egg collection with a needle through the vagina (taking around 20 minutes, with a sedative), a sperm sample from the partner or donor sperm prepared in the laboratory, fertilisation of the eggs in the laboratory, and transfer of an embryo into the womb after a few days. Leftover suitable embryos may be frozen.

It is at the fertilisation stage that the choice between standard IVF and ICSI is made. The clinic usually decides this with you based on a semen analysis, any history of fertilisation problems, and whether sperm needs to be retrieved surgically.

The HFEA lists situations in which a doctor may recommend ICSI:

• A very low sperm count.

• Sperm that are abnormally shaped (poor morphology) or do not move normally (poor motility).

• A previous IVF cycle in which none, or very few, of the eggs fertilised.

• Sperm that must be collected surgically from the testicles or epididymis, for example after a vasectomy or where a blockage prevents sperm reaching the ejaculate.

• Use of frozen sperm that is not of the highest quality.

• Embryo testing for a genetic condition, where sperm sticking to the outside of the eggs could interfere with the results.

The HFEA says ICSI is unlikely to help if, in the past, poor quality or immature eggs meant the egg and sperm had trouble fertilising. It also says there is currently no scientific evidence to support using ICSI where infertility is not related to the male partner's sperm, and that good practice guidelines from the British Fertility Society and recommendations from the European Society of Human Reproductive Medicine do not recommend ICSI over standard IVF in those circumstances. Opting for ICSI when it is not necessary may add to the cost without clear evidence that it improves success.

This matters because the extra step has a cost and is not free of risk, so any suggestion of ICSI where male-factor infertility is not the problem is worth discussing carefully with the clinic.

The NHS says IVF is a safe procedure and most people do not have problems, but there is a small chance of ovarian hyperstimulation syndrome, and risks include having more than one baby and ectopic pregnancy.

The HFEA says ICSI carries slightly more risks than some other fertility treatments, including a risk that eggs may be damaged when they are cleaned and injected. It says it has been suggested that ICSI may be associated with long-term health issues in the children, though this cannot be proved either way without more conclusive evidence. It notes certain genetic and developmental defects in a very small number of children, which may have been caused by the underlying infertility rather than the treatment, and that a boy conceived by ICSI may inherit his father's infertility, particularly where there is a defined genetic cause such as one involving the Y chromosome. Genetic testing and counselling are options to discuss.

The NHS says eligibility for NHS IVF depends on age and how long you have been trying, and that local integrated care boards decide who is able to have IVF in their area and make the final decision about funding. If paying privately, each clinic sets its own prices. Whichever route, the NHS advises being careful about treatment abroad, where clinics may not be regulated in the same way as in the UK.

Sensible questions for a clinic are: what in my results suggests ICSI over standard IVF, what is the additional cost, and how will the clinic decide on the day if my sample is different from what was expected.