Edinburgh Zoo panda Tian Tian 'has lost her baby' say devastated keepers Zookeepers believe Tian Tian was successfully inseminated but lost foetus Carers had been kept guessing since artificial insemination in April Experts noted signs the fertilisation had been successful in August The zoo today has said it is believed she is no longer pregnant Britain's only female giant panda is no longer pregnant after losing her cub, zookeepers have confirmed. Experts at Edinburgh Zoo believe she was successfully inseminated but lost the foetus at late term. Tian Tian had been keeping her carers at the zoo guessing over her possible pregnancy since she was artificially inseminated in April. Tian Tian, Britain's only female giant panda, is believed to have lost her cub Experts noted signs in August that the artifical insemination in April had been successful and a panda cub had been expected for last month In August, experts noted signs that she had been successfully fertilised and it was hoped a panda cub would be born by September. However, the zoo today said her hormonal and behavioural signs suggested she was no longer pregnant. 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 - she passed a mucus plug around mid-September and began producing colostrum. She also experienced a prolonged secondary-rise in progesterone. The panda's carers at Edinburgh Zoo had been kept guessing whether Tian Tian was pregnant after she was artificially inseminated in April 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, whose name means Sweetie, and male panda Yang Guang, or 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. Tian Tian was artificially inseminated using semen from Yang Guang (pictured) and another panda As recently as last week experts said evidence suggested that a cub would be delivered 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. Pandas find it difficult to conceive because females become fertile just once a year for 36 hours between mid-April and May. Attempts at getting a pair to mate, meanwhile, can often prove fruitless. Even where they are successful, fertilized eggs remain suspended within the panda until an unknown trigger causes it to implant. It is then difficult to determine whether they are pregnant because they do not develop a 'baby bump'. The bears also commonly have phantom pregnancies - Tian Tian had one last year. Mr West added: 'Such a loss has always been in our minds as a very real possibility, as it occurs in giant pandas as well as many other animals, including humans. 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. Speaking at the zoo today, director of the panda project Iain Valentine said: 'What we can say is that when we look at all the data she did conceive, she did get pregnant, and what we're trying to do now is pinpoint where she may have lost her pregnancy. That is quite tricky to do with the information we have got. Why does this happen? We don't truly understand, but what we do know is this is a species which lives on the edge of a balance between nutritional intake and reproducing. Yang Guang (left), the male panda, looks through the fence of his enclosure at Tian Tian as they make their first appearance in Edinburgh on December 12, 2011 'If things aren't quite right this can be a reason why they absorb the young and cancel the pregnancy. We are determined to learn from this experience and if we can improve then we will do. The panda enclosure will remain closed until the end of the week. 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'. 'What we can say is that when we look at all the data she did conceive, she did get pregnant, and what we're trying to do now is pinpoint where she may have lost her pregnancy' Ian Valentine, director of the panda project 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 well-being 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. August 24, 2003: Tian Tian born and reared at Ya'an reserve in Chengdu, China. Yang Guang born 10 days earlier. December 4, 2011: Pandas arrive in Scotland on Boeing 777F flight dubbed 'panda express'. December 16: Hundreds of visitors queue to see pandas on display at Edinburgh Zoo for first time. January 12, 2012: Yang Guang found to be suffering from colic and is temporarily removed from public view. Tian Tian later suffers from same ailment. 'Panda express': The freight aircraft transporting giant pandas Tian Tian and Yang Guang pictured shortly after landing at Edinburgh Airport February 1: Zoo says visitor numbers up 200 per cent thanks to pandas. Around 70,000 people have seen Tian Tian and Yang Guang since their arrival. April 3: Pandas brought together for first time in 'love tunnel' as Tian Tian judged ready to mate. April 5: Zoo says 'sparks flew' between the pandas but they fail to mate. December 2: Just before the pandas' first anniversary at the zoo, keepers say they have had more than 500,000 visitors including Nicole Kidman and the Princess Royal. February 28, 2013: Surveillance cameras ('panda cams') placed in enclosure to monitor the animals as mating season approaches. Tian Tian (left) and Yang Guang (right) were brought together for the first time in the 'love tunnel' in April 2012 April 21: Zoo announces that Tian Tian was artificially inseminated after she displays behaviour not 'conducive to mating' July 15: Rise in Tian Tian's progesterone levels detected. August 9: Keepers say Tian Tian showing signs that she is expecting cub. August 26: Zoo announces that Tian Tian has been placed on 24-hour surveillance after latest hormone tests reveal she could be pregnant. October 15: Zoo announces Tian Tian is no longer believed to be pregnant having lost her cub.