"All of her hormonal and behavioural signs now indicate that she had conceived and carried a foetus until late term, but then lost it," Ediburgh Zoo said in a statement about the panda named Tian Tian.
Royal Zoological Society of Scotland chief executive officer Chris West 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."
Tian Tian also experienced a prolonged secondary rise in progesterone.
However, the veterinary team noticed a significant decline in the amount of colostrum being produced by her over the last few days even as Tian Tian returned to normal eating and behavioural patterns like a non-pregnant panda.