Tian Tian, the only female giant panda in the UK, is believed to be pregnant and could give birth as early as Friday (25 August).
Edinburgh Zoo it preparing itself to deliver the UK's first ever panda born in captivity, following several failed attempts.
Tian Tian arrived at Edinburgh Zoo in 2011 but has never been able to naturally get pregnant with Yang Guang, the male panda who joined her at the zoo following a deal with China that sees them rent the pair for around £600,00 a year.
Tian Tian was believed to be pregnant in 2013 following changes to her hormone levels and nesting behaviour but it later turned out to be a phantom pregnancy – surprisingly common in the panda world.
She has been artificially inseminated five times since last year after the zoo decided there was no prospect of Tian Tian and Yang Guang ever mating naturally.
An email, from 25 July by Iain Valentine, director of giant pandas at the Royal Zoological Society of Scotland (RZSS), to the Scottish Government and seen by the Scotsman, stated: "TT doing real well. As things are at the moment, she seems on track but I have shifted possible birth date to around 25th August. Will be able to be a bit more precise in a week's time.
"So she is about 30 days out now and pregnancy proper has now begun in what we think is a 37 day pregnancy. "
A spokesperson at Edinburgh Zoo said: "Giant panda breeding is a very complicated process but we believe that Tian Tian is pregnant.
"Although a specific date was suggested, like all babies, it's hard to predict precisely and the panda breeding season can last until late September.
"Tian Tian is being closely monitored by our expert team and we will be the first to share any news as soon as we can."