Many NHS trusts in England are failing to follow government guidance to fund one full round of IVF treatment, a Department of Health survey has found.
The poll found fewer than half of NHS trusts fund the freezing of spare embryos created during treatment, and their implantation if required.
The National Institute for Health and Clinical Excellence (NICE) says this should be part of NHS-funded care.
The poll also found some people are being denied IVF completely.
The findings were revealed in a letter sent by Health Minister Dawn Primarolo to Primary Care Trusts, which fund NHS treatment.
The letter also highlighted continuing wide variations in the provision of IVF treatment across England.
It revealed confusion over how to implement the NICE guidance and variations over which couples are deemed suitable for IVF.
In its 2004 guidance, NICE said the NHS should fund three cycles of IVF for eligible couples where the woman was under 40.
The then Health Secretary John Reid said couples would be offered one free IVF cycle with a view to three cycles being offered in future.
The Department of Health is working with the charity Infertility Network UK to develop standardised rules on access for IVF.
The government also announced last month it would be monitoring fertility treatment provision across the country.
A recent all-party committee of MPs concluded that IVF remains a low priority for many in the NHS.
And the difference in provision across England was highlighted by work carried out by Conservative MP Grant Shapps earlier this year.
He said: "When I undertook a review earlier in the year, I was alarmed to see the extent to which PCTs varied their level of treatment.
"This latest research seems to indicate that the disparity of provision of important elements like frozen embryo transfer is even greater than first thought.
"The idea that, in half of cases, frozen embryo transfer is not included in a single cycle will alarm couples undergoing IVF treatment."
Clare Brown, chief executive of Infertility Network UK, said: "It is unacceptable that many PCTs are failing to include frozen embryo transfers as part of their IVF cycles.
"This is vitally important given the likely move towards single embryo transfer for appropriate patients.
"We also believe it is unacceptable to create something as special as an embryo on the NHS but only to allow it to be transferred if you have the ability to pay."