National Zoo panda Mei Xiang may be pregnant.

“The keyword here is may,” zoo spokesman John Gibbons said. The panda has had two false pregnancies in 2003 and 2004, respectively.

If Mei Xiang is pregnant, she would deliver a baby sometime in July.

Giant pandas experience a delayed implantation of the egg, according to the zoo. They emit hormones from 50 to 130 days after conception. These hormones are emitted during ovulation regardless of conception, so it’s difficult to determine with certainty whether a panda is pregnant because her body will appear to be conceiving for 50 to 130 days.

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“Female pandas go into heat only one time a year,” Gibbons said. “They are only ovulating for 24 to 48 hours versus humans that ovulate once a month. There is a very small window of opportunity for pandas to breed.”

Tai Shan, Mei Xiang’s first cub, was born at the zoo on July 9, 2005, and has been a big draw at the zoo ever since. He has been fully weaned from his mother and lives in a separate enclosure at the zoo’s Asia Trail exhibit.

Giant pandas are an endangered species. The wild population is an estimated 1,300 to 1,500, Gibbons said, and they are facing devastating loss of habitat in China. Scientists also know little about how pandas breed in the wild.

Captive breeding also poses another challenge — inbreeding. Like humans, pandas need genetic diversity. American zoos have very few giant pandas — eight compared with China’s 200. Compounding the problem, Gibbons said, is that in “captivity in the United States we have very few animals that are compatible either genetically or logistically.”

The Associated Press contributed to this story.