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Live camera monitoring expectant panda

Giant panda, Bai Yun, expecting cub

Bai Yun, seen in 2005, when she was pregnant with twins.

SAN DIEGO, California – The San Diego Zoo is on baby watch.

Bai Yun, a 20-year-old giant panda, is expecting a cub.

Thursday, an ultrasound showed a panda fetus and detected a heartbeat.

Zookeepers, veterinarians, nutritionists and scientists are among those keep a round-the-clock watch for the panda's delivery. Because of her age, Bai Yun's pregnancy is considered high-risk. She will be one of the oldest giant pandas known to give birth.

The zoo has set up a live web cam to allow others to watch Bai Yun's progress.

A press release from the zoo said: "Following signs of estrus in March 2012, Bai Yun was paired with Gao Gao, a 20-year-old, rescued, wild-born giant panda. This pair has produced four cubs while they have lived at the San Diego Zoo.

A panda's fertilized egg remains suspended until a trigger in the environment indicates it is time to implant. The trigger is still unknown to scientists. Giant pandas routinely delay the implantation of the fetus as long as four months. The team estimates implantation occurred in Bai Yun six to seven weeks ago. After implantation the fertilized egg begins to develop. Impending birth is predicted on the basis of behavioral, hormonal and anatomical changes documented by scientists at the San Diego Zoo's Institute for Conservation Research."