Tian Tian may have carried a fetus until late into a pregnancy, officials told The Guardian Tuesday.
Senior zoo officials said they were "incredibly disappointed" after biological and behavioral evidence indicated Tian Tian had lost her baby late in pregnancy, reabsorbing the fetus after signs she had been close to giving birth.
"We are all saddened by this turn of events after so many weeks of waiting," zoo head Chris West said. " 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."
Tian Tian was artificially inseminated 6 months ago after failing to mate naturally with her zoo partner Yang Guang.
Tian Tian has given birth before, bearing cubs in Beijing in 2009, while Yang Guang has successfully fathered cubs once, zoo officials said.
Plans are being made for next spring when an attempt will be made to encourage the pair to mate during Tian Tian's fertility windows, a narrow opportunity of time lasting only around 36 hours.
Captive panda often need three or four such attempts to successfully produce young, the zoo said.