Following a final ultrasound and hormone analysis, staff at the Smithsonian’s National Zoo confirmed late yesterday (Tuesday, April 27) that female giant panda Mei Xiang (may-SHONG) is not pregnant but was experiencing a pseudo, or false, pregnancy during the past several months.

Image right: National Zoo staff perform an ultrasound examination on giant panda Mei Xiang.

National Zoo scientists, veterinarians, keepers and volunteers from the Friends of the National Zoo were keeping a close eye on Mei Xiang, monitoring her hormone levels and behavior, as well as conducting weekly ultrasound exams in an attempt to determine if she was pregnant. On April 22, Mei Xiang’s progestagen concentrations had declined sufficiently to start the 24-hour watch. On reaching normal baseline levels, this decline ends in either the birth of a cub or the end of a pseudopregnancy. Based on current hormone analyses, and not having seen a fetus during the ultrasound exams, Zoo researchers have determined that Mei Xiang experienced a pseudopregnancy.

Image left: Mei Xiang (Meghan Murphy photos)

Female giant pandas almost always undergo a pseudopregnancy when they ovulate but fail to conceive. During a pseudopregnancy, hormonal changes and behaviors are identical to those of a true pregnancy, making it very difficult to determine if a giant panda is actually pregnant or not. This is the fifth time Mei Xiang has had a pseudopregnancy. Giant pandas ovulate only once a year. Mei Xiang gave birth in 2005 to Tai Shan, who was sent to Wolong’s Beifengxia Base in Ya’an, Sichuan, China, in February to join its breeding program.

National Zoo staff expect Mei Xiang to return to normal, hormonally and behaviorally, in the coming days, which includes an increase in appetite and activity level. The Fujifilm Giant Panda Habitat will reopen today at 10 a.m. It had been closed to provide Mei Xiang with a quiet environment in the event that she did give birth.

Giant pandas are endangered; scientists estimate there are around 1,600 remaining in the wild.

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Photo: Staff from the National Zoological Park perform an artifical insemination on the giant panda Mei Xiang, anesthetized and laying on her back at lower center. (Photo by Mehgan Murphy)

Both pandas were anesthetized, allowing the scientists to collect semen from Tian Tian and insert it directly into Mei Xiang’s uterus. Timing was critical because female giant pandas ovulate only once a year. A short period of two to three days around ovulation is the only time she is able to conceive. Gestation typically lasts from 90 to 185 days. This range is due to a reproductive phenomenon known as “delayed implantation,” or the delay from the point of conception to the point of implantation in the uterine wall.

“We will begin monitoring Mei Xiang’s behavior, conducting regular ultrasound examinations and analyzing certain hormone levels in the coming months to help us determine if she is indeed pregnant,” said Suzan Murray, chief veterinarian at the National Zoo. “This can be challenging, however, because pandas can also experience a pseudopregnancy.” Female giant pandas undergo pseudopregnancies when they ovulate but fail to conceive.  During a pseudopregnancy, hormonal changes and behaviors are identical to a true pregnancy.

Photo: Mei Xiang (Photo by Ann Batdorf)

Both 11-year-old Mei Xiang and 12-year-old Tian Tian were born at the China Research and Conservation Center for the Giant Panda in Wolong, China. They came to the National Zoo in December 2000. Mei Xiang has had several pseudopregnancies since, but successfully gave birth to a male cub, Tai Shan (tie-SHON), on July 9, 2005.

The reproductive success of Mei Xiang and Tian Tian at the National Zoo is only a small part of the contributions to giant panda conservation being made by the Smithsonian. Scientists from the Institution have been working diligently in China since 1996, assisting Chinese colleagues in improving reproductive and health success of giant pandas in Chinese breeding centers and working in the field to help save the species in nature.

Photo: Tian Tian (Photo by Jessie Cohen)

There are an estimated 1,600 giant pandas remaining in a few mountain ranges in central China, in Sichuan, Shaanxi, and Gansu provinces. They once lived in lowland areas, but farming, forest clearing, and other development now restrict giant pandas to the mountains. The species is listed as “endangered” by the International Union for Conservation of Nature and Natural Resources. —Johnny Gibbons

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1. National Zoo’s giant panda Mei Xiang is not pregnant
2. Baby Boom of Endangered Species at Smithsonian’s National Zoo’s Conservation and Research Center
3. Women in Science: Working with giant pandas at the National Zoo

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