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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  • Tai Shan takes a short plunge off the edge of a faux rock during his debut to the press November 29, 2005 at the National Zoo. Tai Shan was sent to China in February, 2010.

  • Mei Xiang and Tai Shan, who was born at 3:41 a.m. July 9, 2005, weighing only a few ounces at birth. This photo was taken in December, 2005.

  • Giant Panda cub Tai Shan cuddles with his mother, Mei Xiang, while they eat melon balls in the morning at the National Zoo's Giant Panda Habitat on August 30, 2006.

  • Giant Panda Tian Tian plays with a box on January 20, 2011 at the National Zoo. The snack is made with apples and pears frozen in apple juice.

  • Giant Panda Mei Xiang eats a breakfast of bamboo at the National Zoo's Giant Panda Habitat on August 30, 2006.

  • Giant Panda Tian Tian enjoys a fruitcicle at the National Zoo on January 20, 2011.

  • The 4th Birthday Of Giant Panda

    Giant panda Tian Tian eats bamboo at the National Zoo on July 9, 2009.

  • Tai Shan officially celebrated his fourth birthday with singing, guests and a massive, three-tiered "veggie-sicle" cake. The frozen masterpiece was made over the course of two weeks by Zoo commissary staff by freezing a combination of water, beets and beet juice while enhancing it with bamboo and fruit. Tai quickly took to the frozen treat, licking at the ice, spotting his furry face with the melting beet juice.

  • Panda cub Tai Shan is examined, weighed and measured on September 19, 2005.

  • The National Zoo's Chief Veterinarian Dr. Suzan Murray, Curator of Primates and Giant Pandas Lisa Stevens and animal keeper Nicole Meese conducted a health exam on Tai Shan when he was a cub in 2005.

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.

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