It's that time of year again: the National Zoo's panda may—or may not be—pregnant.
The zoo announced today that Mei Xiang's urinary progesterone has spiked since mid-July, indicating that she may just give birth to another panda cub within the next 40 to 55 days.
Or not. Panda procreation is a surprisingly complex science, and many pandas experience pseudopregnancies, showing all signs of pregnancy but not actually producing a panda cub. Scientists can only be sure of a pregnancy when a panda cub emerges.
Mei Xiang was artificially inseminated twice in late March after natural breeding attempts with her on-again, off-again mate, Tian Tian, didn't pan out. Sperm from both Tian Tian and a male panda from San Diego, Gao Gao, was used.
The National Zoo's resident female panda gave birth to a cub in September 2012, but it died after only a week due to lung and liver damage. Before that, Mei Xiang produced Tai Shan—affectionately known as "Butterstick" after his size at birth—in 2005. She has also had five failed pregnancies.
Mei Xiang's enclosure will be closed to allow her to nest in peace, but the public can watch her on the zoo's panda cam.