Edinburgh Zoo said Tian Tian (Sweetie) has started to produce colostrum (milk) and is still being monitored "around the clock" by experts.
Panda breeding is not an exact science and it remains ''really difficult'' to tell if a female panda is expecting a cub, the zoo said in a statement.
Tian Tian has been keeping her keepers, and the public, guessing over her possible pregnancy since she was artificially inseminated in April.
In August, Edinburgh Zoo said she was showing encouraging signs of pregnancy and Tian Tian was later placed on 24-hour surveillance, with early expectations that she could give birth in late August or September.
When that did not materialise, the zoo cautioned that any birth could happen two weeks later than previously thought.
Now it remains the case that no-one can say for sure whether the panda is pregnant, or, if she is, when she might give birth.
Edinburgh Zoo said it is still possible Tian Tian is expecting and they will continue to prepare for a new arrival.
Simon Girling, head of veterinary services, said: "We know it seems hard to believe after all this time but Tian Tian, our female giant panda, is still continuing to show signs of being in the late term of pregnancy.
"Her behaviour has mellowed out over the past few days, which is a very positive sign, and she has also started to produce colostrum.
"As pandas experiencing a pseudo-pregnancy also produce colostrum and behave just as a pregnant panda would, these signs are still not 100% indicative of pregnancy, but while Tian Tian continues to show signs of late-term pregnancy we will continue to treat her in that way, which means allowing her to enjoy time off show while keepers monitor her around the clock."
Meanwhile, the zoo said that male panda Yang Guang has been "off colour" and was recently removed from display due to illness.
It is believed he has a metabolic disorder but should recover in a couple of weeks.
Mr Girling said: "As with any other animal in our collection, we carried out some routine blood sample and imaging tests on Monday September 16 and thankfully nothing major was found.
"We believe he may have a minor metabolic disorder with reduced blood levels of calcium and since starting a regime of supplements he has shown significant improvement and his keepers are really happy with him. We expect him to recover in a matter of weeks."
The pandas arrived at Edinburgh Zoo from China in December 2011. Zoo bosses hoped the pair would mate naturally when she came into season.
But animal experts ruled out putting them together after assessing her behaviour and Tian Tian was artificially inseminated using semen from Yang Guang and another panda.