Panda pregnancy still a mystery
The UK's female giant panda is keeping zoo keepers guessing over her possible pregnancy.
If Tian Tian is to give birth, it may happen two weeks later than previously thought, experts at Edinburgh Zoo have said.
Keepers are monitoring the panda 24 hours a day and suggested on August 26 that she could produce a cub within the fortnight.
In an update, the zoo said: "In terms of Tian Tian's possible pregnancy, we're not out of the game yet although she's keeping us on our toes. Her hormones are following an atypical pattern, with lots of rises and dips, which make timings much harder to predict.
"We are continually analysing hormone and protein samples and, based on the latest results, our external experts now believe Tian Tian may have experienced her secondary progesterone spike two weeks later than the results previously available suggested.
"Predicting pregnancy in giant pandas isn't straightforward and we're all rapidly learning that Tian Tian is a panda whose behaviour and physiology appears to be more complicated than most."
Experts are not certain at this stage if Tian Tian is pregnant but hormone tests are said to show positive signs and she is being closely watched for signs of labour such as restless behaviour and bleating.
The birth itself could last only a matter of minutes due to the small size of newborn cubs which weigh approximately 100 grams.
Tian Tian and her male companion Yang Guang arrived at Edinburgh Zoo from China in December 2011.
Zoo bosses had hoped the pair, the first giant pandas in the UK for 17 years, 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 in April using semen from Yang Guang and Bao.
Bao, a ''genetically important'' panda who died at Berlin Zoo last year.
If a cub is born a blood test is expected to be carried out by conservation geneticists and confirmed by the laboratory at the Scottish zoo.
Any cub that is born at Edinburgh Zoo will be the property of China and would be expected to return to the country when it is two years old - the age they would naturally disperse in the wild.
Once in China it would join a conservation programme there, either for breeding or reintroduction into the wild.
In keeping with Chinese tradition, any cubs that are born would not be named until they are 100 days old and would only go on display on January 1 2014.
The zoo said that Yang Guang would not have contact with any cub as male pandas play no part in their upbringing in the wild.