Americans are on panda watch after the National Zoo announced that they detected a fetus during an ultrasound of giant panda Mei Xiang.

Based on the size (about four centimeters or 1.6 inches), veterinarians estimate Mei Xiang could give birth early next week, or possibly in early September.

There is a also substantial possibility that Mei Xiang could resorb or miscarry a fetus, the Zoo warned. Scientists do not fully understand why some mammals resorb fetuses.

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The zoo reported that Mei Xiang is spending more time in her den, sleeping more, licking her body more and cradling objects — behaviors consistent with pregnancy or pseudopregnancy.

Scientists from the Smithsonian’s National Zoo and Conservation Biology Instituteartificially inseminated Mei Xiang April 26 and 27, using semen collected from a giant panda named Hui Hui, who lives at the China Conservation and Research Center for the Giant Panda in Wolong, China. Hui Hui was determined to be one of the best genetic matches for Mei Xiang.

This photo of Mei Xiang was taken on June 9, 2005, exactly one month before she gave birth to her first cub, Tai Shan. (Photo by National Zoo)

But scientists also artificial inseminated her with fresh semen collected from the Zoo’s male giant panda, Tian Tian.

If a cub is born, DNA analysis will determine who the father is.

The zoo’s panda habitat will close completely until further notice to provide quiet for Mei Xiang. She will continue to be visible on the panda cams. Friends of the National Zoo volunteers who operate the panda cam and zoo staff will a 24-hour watch.

Mei Xiang has given birth to two surviving cubs, both through artificial inseminations: Tai Shan and Bao Bao. Tai Shan was born July 9, 2005, and he now lives in China. Bao Bao was born Aug. 23, 2013. She will live at the Zoo until she turns 4; at that time, she will also go to live in China and, eventually, enter the giant panda breeding program.

The Zoo will continue to provide daily updates on Mei Xiang through its SmithsonianZoo Instagram account using #PandaStory, and the Giant Panda e-newsletter.

In other panda news, a giant panda gave birth to a cub at the National Zoo of Malaysia in Kuala Lumpur, Prime Minister Najib Razak announced on Twitter on Tuesday.

The panda’s mother Liang Liang and father Xing Xing arrived in Malaysia last year on a 10-year loan for the 40th anniversary of the establishment of diplomatic relations between China and Malaysia.

The gender of the cub has yet to be determined as Liang Liang has kept it hidden in a corner, China Daily reported.