Very obese women should be denied fertility treatment, experts say.
The British Fertility Society is recommending women with a body mass index of 36 and over should not be allowed access to fertility treatment.
Underweight women and those classed just as obese (BMI over 29) should be forced to address their weight before starting treatment, the society said.
NHS guidelines say overweight women should be warned of the health risks, but do not impose any ban on treatment.
Being overweight can put both the health of the mother and child at risk through problems such as gestational diabetes and high blood pressure.
In reality, many primary care trusts do not fund women who are obese.
The BFS has published its recommendations in a bid to end the IVF "postcode lottery".
It wants to standardise treatment so that clinics use the same criteria in relation to age and family status as well as weight.
Obese women are less likely to get pregnant and more likely to encounter health problems
Richard Kennedy, of the British Fertility Society
Q&A: Infertility treatment
'Too fat for IVF'
Richard Kennedy, of the BFS, said: "The NHS is already stopping women who are obese from having fertility treatment.
"What we are saying is that they should be less stringent and more consistent with how they apply this.
"Obese women are less likely to get pregnant and more likely to encounter health problems. It makes sense to address obesity before seeking fertility treatment."
The BFS, which represents health fertility professionals, also recommended single women and same sex couples be given the same priority as heterosexual couples.
Cycles
NHS guidelines say women aged 23 to 39 should be entitled to three cycles of IVF, although the government gave the health service a deadline of April last year to provide one cycle with a view to working towards three.
The society made its recommendations after surveying 64 fertility clinics in England and Wales.
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It received responses from 37, showing one in 10 was not providing IVF treatment free on the NHS because they were not being given funding by the local PCTs.
None of the clinics was providing three cycles, the poll, which will be published in the Human Fertility journal in September, said.
The poll also showed many of the PCTs which did provide IVF treatment were restricting access by taking social factors into account.
These included barring people from treatment if one of the partners already had a child from a previous relationship or because the couple had paid for private treatment before going to the NHS.
And it also revealed a quarter of clinics were also restricting treatment according to age, with most only allowing women in their late 30s to have IVF.
Clinical factors
Dr Gillian Lockwood, who chairs the BFS's ethics committee, told the BBC that "unfairness" was the aspect of the NHS provision which people objected to most.
"Trying to get rid of the postcode lottery is something that's influenced treatments for multiple sclerosis and cancer so it's only reasonable that it should apply to fertility treatment too," she said.
But Dr Lockwood said there were clinical factors which affected the success of IVF and, as well as weight concerns being over the age of 40 meant that "even very high-tech treatments like IVF are really very unsuccessful".
Clare Brown, chief executive of Infertility Network UK said: "From our own surveys and from the many, many calls we receive from patients, we know only too well that there are still unacceptable inequalities in the funding of treatment around the country and couples face huge difficulties in accessing services."
Trying to get rid of the postcode lottery is something that's influenced treatments for Multiple Sclerosis and cancer
Dr Gillian Lockwood
But Josephine Quintavalle, of the organisation Comment on Reproductive Ethics, told BBC Five Live limited NHS budgets needed to be focused on treatment for groups which would benefit the most.
"If it's a proven fact that it's very difficult to get pregnant when you're overweight, then the logical cure for that kind of infertility is to encourage the patient to lose weight."
'In line'
Jo Webber, deputy director of policy at the NHS Confederation which represents over 90% of NHS organisations, said: "We recognise the distressing circumstances that couples with infertility problems find themselves in.
"However, primary care trusts receive a fixed allocation of money to deliver all the services for their local community and have to take difficult decisions on competing priorities."
The Department of Health said that, while it did not support bans being imposed, the current NHS guidelines were broadly in line with the recommendations on obesity.
A spokeswoman added: "Primary responsibility for implementing NICE guidelines, including the rate of implementation, rests with the NHS at local level and we have made it clear that we expect these guidelines to be followed."
She said the government was working with patient group Infertility Network UK to ensure PCTs listened to the views of patients.
