Couples seeking fertility help are being told be wary of how clinics advertise their success rates.
About one in five couples have trouble conceiving and a lot of them seek help. Many clinics across Australia and New Zealand advertise their in vitro fertilisation (IVF) success rates on their websites.
Couples often shop around for the best and most successful clinic to maximise their chances.
But a new study, published in the Australian and New Zealand Journal of Obstetrics and Gynaecology, said the success rates were meaningless because they were calculated in different ways.
A senior author on the report and professor of Obstetrics and Gynaecology, Cindy Farquhar, said it was like comparing apples and pears.
She said there was nothing to stop clinics from selectively advertising their most favourable, rather than relevant, success rates.
All 20 clinics' websites involved in the report were broadly compliant with 2017 trans-Tasman guidelines for success rate advertising.
But the study found that despite the policy there was a lot of variation in the way information was being presented.
"I think you'd have a difficult time and challenge to be able to look at the websites and say you could compare one website with another," Farquhar said.
The policy needed to be strengthened to be clearer and that clinics needed to take ownership of the data and present it in a way people can use it, she said.
Across the websites the researchers counted 32 different ways they had measured "success".
But the best measure of success was cumulative live births per IVF cycle started, which no website reported.
Farquhar told Morning Report because they were not government guidelines there was "a mishmash" of data.
"What's misleading is that ... none of the clinics reported the scenario if I start a cycle of IVF what's the chances of having a baby at the end. All of the clinics were reporting in different ways..."
The thing Farquhar was most critical of was the reporting of success rates when women had an embryo transferred.
But she said approximately 20 percent of couples did not get to have an embryo transferred, and the data doesn't reflect it.
"That should be clearer to patients coming into the clinics.
"As soon as you report it from the number of people who start the cycle, not the number of women who have an embryo transfer, the numbers become a little less optimistic.
"I think we should be honest about that."
She said the current reporting was advertising false hope, and was over-inflating the results.
Farquhar wants to see the policy tightened and be clearer so that all clinics are reporting the same sets of data.
She said it was a very vulnerable time for people because of their age and pressure from friends or family.
"They need to be able to get transparent information so they can clearly say your results are actually the same..."
Lead author of the study, Dr Lucy Goodman, said: "Unfortunately, couples in New Zealand and Australia can't rely on advertised 'success rates' when choosing clinics.
"The problem is, the guidelines don't actually define what counts as 'success'.
"Some clinics describe pregnancy rates from individual embryos - but not all women who start IVF treatment will reach this stage of treatment."
Farquhar said: "Patients come along to the clinic and they look quite perplexed, when they've read online that you can have these fantastic pregnancy rates, but it's because it's per embryo transferred and not per cycle started".
And the stakes were high for couples who seek fertility treatment because of the costs involved, she said.
"If 100 women aged less than 35 start an IVF treatment cycle, only 19 will have a live birth following fresh embryo transfer.
"Fertility patients deserve the best information available, and at the moment they're comparing apples with pears across clinics."
She said some of the differences were women's ages, not including figures for people who had lower fertility, and some clinics used figures for frozen embryos while another would use fresh.