Following artificial insemination in April, the zoo has been tracking Tian Tian’s hormone levels. The one to watch is progesterone. At around the time of ovulation, there is a small rise, with levels remaining roughly constant for several months. At this stage, the embryo is fertilized but is not developing. Then, some 60 to 100 days later, progesterone levels jump again from around 250 ng to 2500 ng (per gram of faeces) and the embryo begins to divide. In a press release, tantalizing entitled “Panda update: definitely maybe!”, Edinburgh Zoo told us that this second rise occurred on 15 July.
According to the latest study of pandas whose pregnancies went to term, a female will give birth, on average, 38.8 days later. There is a large variation though, with the swiftest female giving birth just 26 days after the jump in progesterone and the slowest female 55 days after. If Tian Tian were on the pacey side, she’d have dropped a month ago on 10 August. Even if she were more ponderous, she’d have given birth by now. She has not.
On Friday, Edinburgh Zoo’s chief executive issued a blog post that talked of “a flurry of new births” but made no mention – not even in passing – of Tian Tian’s pregnancy. Today, after much badgering, the zoo finally issued a brief update, saying that “we’re not out of the game." It goes on:
I’m a journalist not a panda biologist, but looking at the graphs of what progesterone does in a pregnant panda, it is somewhat baffling that the zoo could have mis-identified such a massive change in progesterone. They do say that “Tian Tian is a panda whose behaviour and physiology appears to be more complicated than most!”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.
I suppose it’s possible that she’s still pregnant. Or, more likely I’m afraid, she’s not.