San Diego zoo officials announced on Monday that Bai Yun, a giant panda on loan from China, is expected to deliver twins sometime this month.

Because panda pregnancies can vary in length by as much as three months, zookeepers don't know exactly when the babies will be born -- or who their father is.

In March, Bai Yun mated naturally with her new partner, Gao Gao, zoo officials said. After Gao Gao lost interest in Bai Yun a day later, she was artificially inseminated with semen from her former mate, Shi Shi.

Shi Shi and Bai Yun are the parents of 3-year-old Hua Mei, the only surviving giant panda cub born in the United States.

An ultrasound done on Sunday showed that Bai Yun was carrying twins. The test marks the earliest a twin pregnancy has been documented, zoo spokeswoman Christina Simmons said.

Zookeepers hope to study Bai Yun's pregnancy to add to the limited knowledge about panda gestation, Simmons said.

Although it is not unusual for pandas to give birth to twins, the females are sometimes unable to care for more than one cub at a time, zoo officials said.

The second cub may be removed from Bai Yun's enclosure shortly after birth and bottle raised, although zookeepers are taking a "wait and see" attitude, Simmons said.

"If we had a situation where a baby was not being taken care of by the mom, we would step in," Simmons said.

(China Daily August 5, 2003)