Mei Xiang at the National Zoo. (National Zoo)

Part of the National Zoo’s indoor panda exhibit has been closed to public view because the female giant panda Mei Xiang is showing some behaviors consistent with pregnancy or “pseudo-pregnancy,” zoo officials said Tuesday.

For example, she is becoming very sensitive to noise, acting restless and moving around.

“Normally, when she dens, she is mostly sleeping or resting,” said Jennifer Zoon, a spokeswoman for the National Zoo. “If there is noise around her, she’s looking around and moving.”

If she is pregnant, zoo officials said, she could give birth within 30 to 50 days. Her hormones began to rise in late July — a possible sign that she is carrying a cub.

Mei Xiang has already given birth to two cubs — Tai Shan and Bao Bao in 2005 and 2013, respectively. The father of both is Tian Tian.

National Zoo officials say panda Mei Xiang is showing signs that she could give birth to another cub, but warn that she could also be experiencing the end of pseudopregnancy. (WUSA9)

In April, Mei Xiang was artificially inseminated with frozen sperm from a panda in China. It was the first time frozen panda semen had made such a long journey to the zoo for breeding, according to zoo officials. The semen sample belonged to Hui Hui — a 9-year-old panda who lives at the China Research and Conservation Center for the Giant Panda in Wolong, Sichuan Province.

Mei Xiang’s first ultrasound in June didn’t show much and that’s what zookeepers expected. She’s had a few other ultrasounds but in the last few weeks, she has refused to participate in an ultrasound — even with the lure of honey water, a panda favorite.

Zoo officials said Mei Xiang is showing other signs of possibly being pregnant. She is nest building and spending “more time in her den, sleeping more and eating less.”

The zoo’s public relations team has tracked the panda’s pregnancy using the hashtag #PandaStory on social media.

Unlike in humans, where the egg is fertilized and the fetus starts to grow and can be measured, pregnancy isn’t so obvious in a panda, zoo officials said.

A female panda has what’s known as “delayed implantation.” She can have a fertilized egg, which can float in her uterus for weeks before it attaches to the wall of her uterus, according to zoo officials.

And there’s another complicating factor — a mama panda’s hormones and behavior can change in a way that’s the same as if she were pregnant, even when she’s not. That is known as a “pseudo-pregnancy.”

Zoo officials said one reason they do the ultrasounds is to check on the panda’s health and to get her comfortable with having them done because they will become more frequent in her possible pregnancy.

Ultrasounds are the only way to confirm — definitively — if she is pregnant. If she’s pregnant, the fetus starts to develop only a few weeks before birth. The gestation period for a female giant panda is between three and six months.

Viewers can still watch Mei Xiang on the panda cams. And visitors can still see her when she goes to her outdoor exhibit area. Visitors to the zoo can still see other pandas, including Tian Tian and Bao Bao, in their indoor and outdoor exhibit areas.