Panda Pregnancy Watch: National Zoo Says Mei Xiang May Be Expecting Baby (PHOTOS)

WASHINGTON -- It's hard not to get our hopes up about this one.

The National Zoo sent out an announcement on Monday that its female giant panda, Mei Xiang, is pregnant or experiencing a pseudopregnancy -- she'll either give birth or end her false pregnancy in 40 to 50 days, the zoo says.

Mei Xiang is the mate to the zoo's male giant panda, Tian Tian. The two are parents to Tai Shan, who was born in 2005, and was -- to the heartbreak of many Washingtonians -- sent to live at a breeding facility in China in 2010.

This spring, when Mei Xiang and Tian Tian hadn't bred on their own, the zoo took matters in its own hands -- the panda was artificially inseminated twice in late April, both times using semen harvested from Tian Tian in 2005. The second insemination was live-tweeted.

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Giant Pandas

Mei Xiang has had five consecutive pseudopregnancies since 2007. Pseudopregnanies, or false pregnancies, mimic true pregnancies in terms of hormonal and behavioral changes and are nearly impossible to tell apart from actual pregnancies. (And due to delayed embryo implantation, it's hard to see panda fetuses by ultrasound until late in the pregnancy.)

Female giant pandas ovulate just once per year -- usually for a few days between March and April -- and almost always undergo a pseudopregnancy if they don't conceive.

One reason for optimism this time: The zoo reports that after several years of an early estrous cycle, Mei Xiang went into heat in April.

One reason for anxiety this time: If Mei Xiang and Tian Tian don't produce a new cub this year, one or both of the pandas may be sent back to China, replaced with animals who seem better-equipped to produce a baby.

Giant pandas are the rarest member of the bear family and are considered to be endangered, largely due to habitat loss. A decade-old survey found some 1,600 animals in the wild; another 300 to 400 giant pandas live in captivity. Let's hope this year that number goes up by at least one.