Experts have confirmed that Edinburgh Zoo's giant panda Tian Tian has lost her baby.
Experts at Edinburgh Zoo believe she was successfully inseminated but lost the foetus at late term.
A statement said: "All of her hormonal and behavioural signs now indicate that she had conceived and carried a foetus until late term, but then lost it."
Tian Tian (Sweetie) has been keeping her carers at Edinburgh Zoo guessing over her possible pregnancy since she was artificially inseminated in April.
In August, experts noted signs that she had been successfully fertilised and it was hoped a panda cub would be born by September.
Chris West, chief executive of the Royal Zoological Society of Scotland (RZSS), which runs the zoo, said: "We are all saddened by this turn of events after so many weeks of waiting.
"Timings are difficult to pinpoint at this moment, but we had a meeting this morning where Tian Tian's behaviour and hormone results were reviewed and have come to the conclusion that it is very likely she has lost the pregnancy.
"Up until now, Tian Tian has consistently shown signs of pregnancy. However, the veterinary team has noticed a significant decline in the amount of colostrum being produced and over the last few days she has returned to the normal eating and behavioural patterns of a non-pregnant panda."
Tian Tian and male panda Yang Guang (Sunshine) arrived at Edinburgh Zoo from China in December 2011.
Zoo bosses hoped the pair would mate naturally when she came into season.
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.
As recently as last week experts said evidence suggested that a cub would be delivered.
Tian Tian had started to produce colostrum and preparations were being made for the much-anticipated arrival.
Meanwhile, Yang Guang has been ''off colour'' and was recently removed from display due to illness.
The zoo said "everything possible" had been done to give Tian Tian the best care during her pregnancy.
Mr West said: "Our dedicated team of keepers, veterinary staff and many others worked tirelessly to ensure Tian Tian received the best care possible, which included remote observation and closing the panda enclosure to visitors to give her quiet and privacy.
"We are conducting a detailed review of the scientific data collected, but I am totally confident that we did everything it was possible to do.
"The majority of research centres and zoos with giant pandas around the world have not successfully bred until the third or fourth year and what we have achieved, considering we have had giant pandas for less than two years, is immense.
"New hormone research is beginning to indicate that lost pregnancies are more common in giant pandas than first thought, though at the moment no-one knows why."
The panda enclosure will remain closed until the end of the week.
Female pandas only ovulate once a year, giving a window of 36 hours in which they can get pregnant.
Tian Tian was inseminated on April 21 using semen from Yang Guang and frozen semen from Bao Bao, a ''genetically important'' panda which died in Berlin Zoo last year.
The gestation period is typically five months.
If a cub had been produced it would have been the property of China and would have been returned to the country after two years to join a conservation programme there.
Mr West said: "We are working as part of a global giant panda conservation programme and will continue to work closely with our international colleagues.
"The research and work we do here goes towards better understanding giant panda biology, education and conservation in the wild, as demonstrated by the Giant Panda Research Symposium held here in September.
"Giant pandas are brilliant ambassadors for other endangered species like Scottish wildcats, basking sharks, bumblebees and butterflies. We exist to safeguard species from extinction. We will carry on and are confident we will succeed."
Edinburgh-based charity OneKind is opposed to breeding wild animals in captivity and criticised the zoo for the lengths it has gone to to intervene "in what should be a natural process".
Chief executive John Brady said: "Edinburgh Zoo has gone through a rigorous and extensive process in a bid to bring a panda cub to Scotland and one needs to ask whether or not this was in the panda's best interests.
"There are questions around the morals of the zoo's breeding programme which must be asked in light of the developments with Tian Tian and her pregnancy which she endured under an intense media and public spotlight."
Mr Brady added: "The entire process of trying to bring a new life into the world in such unnatural conditions is fundamentally wrong.
"While we are extremely saddened by the possibility of a miscarriage and concerned for the wellbeing of the panda at this time, we need to think about the life a panda cub would have had at the zoo, being unable to forage, feed and roam free as nature intended.
"We sincerely hope the zoo will take this into consideration as it carries out its review into its breeding programme."
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