Last month, German professor Gert-Peter Brueggemann, who conducted tests on the prosthetic limbs, said the blades give the 21-year-old South African a competitive edge.
An official statement announcing the finding was first expected Thursday by the International Association of Athletics Federations. However, the ruling has been delayed by two days to give Pistorius and his advisers time to respond.
"There will be no official announcement until the 12th," IAAF spokesman Nick Davies said from Monte Carlo, Monaco.
The IAAF adopted a rule last summer prohibiting the use of any "technical aids" deemed to give an athlete an advantage over another.
Pistorius was born without fibulas - the long, thin outer bone between the knee and ankle - and was 11 months old when his legs were amputated below the knee.
He began running five years ago to treat a rugby injury, and nine months later won the 200 meters at the 2004 Paralympic Games in Athens.
Pistorius has set world records in the 100, 200 and 400 in Paralympic events. To make the Olympics in Beijing, Pistorius would still need to qualify for the South African team and make the qualifying times.
Pistorius worked with Brueggemann in Cologne over several days of testing in November to see to what extent the j-shaped carbon-fiber "Cheetah" extensions to his amputated legs differed from the legs of able-bodied runners.
Brueggemann told Die Welt newspaper last month that, based on his research, Pistorius "has considerable advantages over athletes without prosthetic limbs who were tested by us."
"It was more than just a few percentage points. I did not expect it to be so clear," he added.
Brueggemann and his scientists tested Pistorius' energy consumption and compared it with data of able-bodied athletes of the same speed.
The IAAF is basing its decision on Brueggemann's work, and the ruling is expected to go against the runner. Pistorius could then appeal and ask for further tests.
Ossur, the Icelandic company which is a leader in the production of prosthetics, braces and supports and made Pistorius' Cheetahs, disagrees with Brueggemann's findings.
Ossur CEO Jon Sigurdsson wrote recently to the IAAF, telling the federation that Pistorius "does not have a technical advantage over able-bodied athletes. Based on biomechanics alone, it is simply not possible for him or any amputee to have an advantage over the able-bodied."
Pistorius - nicknamed the "Blade Runner" - competed in the 400 at two international-level able-bodied meets in 2007. He finished second in a "B" race in 46.90 seconds at the Golden League meet in Rome on July 13 and, two days later, was disqualified for running out of his lane in Sheffield, England.