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San Diego Zoo says giant panda expecting her fourth cub

A giant panda at the San Diego Zoo is pregnant again and expecting her fourth cub sometime in August.

The zoo said Tuesday that 16-year-old Bai Yun was put on "24-hour birth watch" after officials detected a fetus and fetal heartbeat through ultrasound images July 18. Additional tests confirmed the pregnancy was going normally.

Her first baby, Hua Mei, which was born in August 1999, has given birth to three sets of twins since moving to China in 2004, including a pair in July.

Mei Sheng, a male panda born in August 2003, will leave the San Diego Zoo in October to join China's breeding program. Bai Yun's third cub, Su Lin, was born in August 2005.

Bai Yun, which translates as White Cloud, appears to have been impregnated seven or eight weeks ago by Gao Gao, the father of her two youngest cubs, the zoo said.