San Diego Zoo officials say their prized giant panda is pregnant again.
Seventeen-year-old Bai Yun already is a mother of four.
Officials say ultrasound tests this week showed a panda fetus and there may be a twin.
Zoo veterinarian Meg Sutherland-Smith says Bai Yun is due next month. Her offspring will weigh just 4 ounces. Bai Yun and the cub will remain in a den for four to five months.
The father is zoo panda Gao Gao. The two mated in April.
Two of Bai Yun's cubs are at the zoo and two are in a breeding program in China.