On Monday, the ACCC said "several major IVF clinics" and some smaller ones had been asked to change claims on their websites following an investigation into the increasingly competitive and profitable industry.

The ACCC refused to name the IVF clinics but Commissioner Sarah Court said a significant number had been notified of potentially illegal behaviour, and that patients had reported some doctors for making misleading claims about their chances of success during consultations.

"In a market like this, what you can often see is ... a bit of a race to the bottom where one firm starts doing it and another copies it," she said.

Were you misled by an IVF clinic? Contact Jmedew@fairfaxmedia.com.au

Ms Court said the ACCC reviewed the websites of Australia's 34 IVF providers and found that some were making success rate comparisons without adequate disclosure about, or qualification of, the nature of the data used to make the claims.

She said some IVF clinics had been advertising success rates of up to 90 per cent within two cycles for women in their 30s based on their own in-house data, looking at people who had never tried treatment before. The data excluded clients who had unsuccessful cycles or who had moved clinics after failed attempts, skewing the results.

Ms Court (above) said some clinics were also using technical terms that could be misleading to consumers without further clarification or explanation. For example, she said some IVF clinics were using data on the creation of embryos in laboratories and 'clinical pregnancies' as success rates, rather than live birth rates.

This is despite data showing not all embryos result in pregnancies and about one in four pregnancies ends with a miscarriage. In some cases these success rate claims were accompanied by photographs of newborn babies - a decision the ACCC said was likely to be misleading.

Ms Court said given many people paying for IVF were vulnerable and desperate to have a baby, it was "particularly egregious" behaviour. However, she said because the conduct was widespread throughout the industry, the ACCC had made a strategic decision to work with providers and fire a "warning shot", rather than enter years of legal action that might delay more honest behaviour.

"We feel like they're squarely on notice," Ms Court said.

A spokeswoman for Genea, one of the largest IVF providers in Australia, said it had made "small changes" to the way it illustrates its success rates on its website this year. However, she said it was not in response to the ACCC investigation, but rather "anticipation of the development of an agreed set of reporting standards".

Thousands of Australians are paying about $5000 in out of pocket fees for single IVF cycles each year without any independent data on clinics' success rates to help them choose a provider. Data which does not name individual clinics shows the live birth rate resulting from IVF treatment varies wildly across clinics, ranging from 4 per cent to 31 per cent.

President of the Fertility Society of Australia Professor Michael Chapman welcomed the ACCC's warnings and said some advertising was making IVF clinics and their staff look like "used car salesmen".

He said a new code of conduct being developed by the Fertility Society of Australia would recommend clinics only publish live birth rates per embryo transfer and cumulative pregnancy rates over time for people according to how many cycles they undertake.

Professor Chapman said the code would also recommend clinics not advertise "breakthroughs" without peer-reviewed research. He said patients should ask fertility specialists about their individual chance of success based on their age, weight, and other circumstances.

While some countries have introduced league tables for IVF success rates, Professor Chapman opposed them because they could induce clinics to reject unfavourable patients, or transfer multiple embryos to improve success rates even though the practice increases the chance of higher risk pregnancies.

Ms Court said the ACCC would continue to monitor IVF providers and prosecute them if they flout the law. Penalties for false, misleading and deceptive conduct include fines of up to $1.1 million.

She said people concerned about being misled by success rate claims could make complaints to their clinics, which may offer refunds. People can also complain to health regulators, including the Australian Health Practitioner Regulation Agency and the Medical Board of Australia.