The amount IVF providers can charge the NHS in England for treatment should be capped by the government, a leading fertility expert has said.
Create Fertility medical director Prof Geeta Nargund said some NHS clinical commissioning groups (CCGs) paid more than twice what others paid per cycle.
A national tariff would allow some regions to offer more women and couples treatment, she added.
CCGs pay clinics to provide fertility treatment for patients on the NHS.
'Level playing field'
The amount paid by CCGs per cycle can range from less than £3,000 to more than £6,000, according to data collated by campaign group Fertility Fairness in 2014-15 through the Freedom of Information Act.
Prof Nargund told the BBC's Victoria Derbyshire programme it would be for economists and CCGs to decide a fair and realistic cap, suggesting this could fall between £3,000 and £3,500 per cycle. It would be the Department of Health's responsibility to implement it, she added.
She said this would "level the playing field for women and couples all across the UK".
"It would allow us to double the number of IVF treatments that can be offered within the existing budget in many regions," she added.
Prof Nargund said there were a number of ways the more expensive providers could cut the cost of cycles - including reducing the number of drugs used.
She pointed to existing tariffs used for the provision of hip replacements and heart operations as an example of how the system could work.
Prof Nargund said the variation in fees was causing some CCGs to fail to meet guidelines set by the National Institute for Health and Care Excellence (NICE).
NICE recommends that women under 40 should have access to three cycles of treatment, but only 38 of the 209 CCGs in England currently offer this, research from Fertility Fairness suggests.
Susan Seenan, chief executive of Infertility Network UK, said that patients "remain at the mercy of their postcode" as a result of the current system.
She added: "A basic IVF procedure is the same no matter which clinic is used. There is a limited amount of drugs they can use, so there shouldn't be a massive difference in price - not to the levels we're seeing in our data."
Ms Seenan said CCGs often did not know how much they should be paying for treatment. "Some appear to take the price they're given or don't question what is included in the cycle," she said.
Prof Nargund and Ms Seenan suggested CCGs should work together to improve their commissioning process and create economies of scale.
The Department of Health has not yet responded to our request for comment.
The Victoria Derbyshire programme is broadcast on weekdays between 09:15-11:00 BST on BBC Two and the BBC News channel.