Past breeding efforts by the zoo have produced three surviving cubs — Tai Shan in 2005, Bao Bao in 2013, and Bei Bei in 2015.

giant panda Mei Xiang

Mei Xiang, a giant panda at the National Zoo in Washington, D.C., may give birth as early as this week.

Veterinarians at the Smithsonian's National Zoo announced on Friday that they detected what looks like a fetus during the giant panda's ultrasound earlier in the day, but are cautioning everyone to not get too excited.

"It is too early to determine if the tissue is a completely viable developing fetus as there is the potential that the fetus could be resorbed," the Smithsonian's National Zoo & Conservation Biology Institute said in a press release.

But if the fetal tissue does continue to develop, veterinarians at the zoo predict Mei Xiang could welcome a new panda cub or multiple cubs in the next few days.

Mei Xiang was artificially inseminated earlier this year in March using semen from the zoo's male giant panda, Tian Tian.

According to the National Zoo, the panda gestational period ranges from 90 to 180 days and the average panda pregnancy lasts 135 days. But panda pregnancies are tricky because the bears often go through pseudopregnancies, "where they do everything they would if they were pregnant," the zoo shared. "At the end of a pseudopregnancy, however, hormone levels return to baseline and females’ energy levels and behavior return to normal."

In late July, Mei Xiang exhibited behaviors consistent with pregnancy and she is now sleeping more, eating less, nest-building, and has been observed body licking. The zoo is cautiously optimistic this apparent pregnancy will result in at least one cub.

"In the middle of a pandemic, this is a joyful moment we can all get excited about," Don Neiffer, chief veterinarian at the Smithsonian’s National Zoo who conducted the ultrasound, said. "We are optimistic that very shortly she may give birth to a healthy cub or cubs."

He added, "We’re fortunate that Mei Xiang participated in the ultrasound allowing us to get sharp images and video. We’re watching her closely and welcome everyone to watch with us on the panda cams." Mei Xiang's ultrasound can be viewed on YouTube.

The 22-year-old panda's fetal tissue was first discovered last week, according to the zoo, who also warned that Mei Xiang could reabsorb the fetus or even have a miscarriage.

"Veterinarians first detected fetal tissue last week, and they have since noted developing skeletal structure and strong blood flow within Mei Xiang’s uterus," the press release said. "If the fetal tissue resorbs, her hormones will return to baseline levels and her behavior will return to normal."

Female pandas are only capable of conceiving a cub for 24 to 72 hours once a year, making the feat very difficult, but all the more exciting.

Past breeding efforts have produced three surviving cubs — Tai Shan in 2005, Bao Bao in 2013, and Bei Bei in 2015. All three pandas were sent to China upon turning four years old, as part of an agreement with the country to preserve the species. The zoo’s current cooperative breeding agreement expires in December 2020.

This story originally appeared on People.