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Scientists at the National Zoo say their female giant panda's hormones are rising, which indicates she may be pregnant or -- if history offers an example -- experiencing a false pregnancy.
Mei Xiang was artificially inseminated twice on March 30 after failing to breed naturally with the zoo's male panda Tian Tian.
Tian Tian has been said to have a flawing breeding technique.
A Chinese panda expert performed the inseminations with zoo scientists, using previously frozen semen from both Tian Tian and Gao Gao, a panda at the San Diego Zoo.
The zoo says its panda team is monitoring Mei Xiang closely and conducting ultrasounds to look for a possible fetus. The pregnancy or pseudopregnancy should end in 40 to 55 days -- which means, if there's a cub, it could be born in the range of Sept. 4-19.
Recently, Mei Xiang has begun nest building. The zoo says that's consistent with her rising hormones.
Mei Xiang has been inseminated annually but has given birth to two cubs.
A female cub, born last September, lived only a week. Her birth was a surprise; she had not shown up on any ultrasounds. An autopsy determined she may have been born prematurely.
Mei Xiang's only surviving cub, Tai Shan, was born in 2005 and now lives in China.