Giant panda "Hua Mei" giving birth to a cub at the Wolong Giant Panda Protection and Research Center in southwest China's Sichuan Province. "Hua Mei" gave birth to twins Wednesday night, which weighed 157 grams and 130 grams respectively.

The American-born female giant panda Hua Mei gave birth to twin panda cubs Wednesday, the China Wolong Giant Panda Protection and Research Center announced Thursday in Chengdu.

The panda cubs weigh respectively 157 grams and 130 grams. Currently, both the mother and baby pandas are healthy and sound, said Huang Yan, a deputy chief engineer at the center.

Hua Mei showed the sign of delivery at Wednesday noon. It took six hours before she smoothly delivered the first cub. In less than an hour, she gave birth to another panda baby. Though tired, the mother panda is normal.

Considering that Hua Mei lacks experience in raising baby pandas as a mother for the first time in her life, scientists at the Wolong center took away a male panda cub for artificial upbringing.

Hua Mei, meaning "China-America," was the cub of Bai Yun and Shi Shi, a panda couple leased by China to the San Diego Zoo, California, U.S. in 1996 as part of a 12-year research cooperationprogram between the two nations.

The five-year-old Hua Mei is the first overseas-born panda. Upon returning to China last February, Hua Mei underwent a month-long observation. When she became accustomed to the new environment, Hua Mei mated with another panda, Ling Ling, and was found pregnant on May 2.

Giant panda "Hua Mei" licks her newly-born baby at the Wolong Giant Panda Protection and Research Center in southwest China's Sichuan Province Sept. 1, 2004.

A female panda normally becomes sexually mature at four to fiveyears old. They only get pregnant once a year, giving birth to oneor two cubs at a time. Panda gestation lasts 83 to 181 days. As pandas mate each other only in three or four days between March and May each year, they have a relatively low fertility rate.

Pandas are among the world's most endangered wildlife. Statistics from the State Forestry Administration released this June show the number of pandas in the wild in China has risen by more than 40 percent from 1,110 in the 1980s to 1,590 nowadays, while a total of 161 are in captive breeding programs worldwide.

However, while the panda population has increased, the animal'sexistence is menaced by loss of habitat and a low rate of reproduction. Also, groups of pandas live far from each other, making breeding even more difficult.

The Wolong center, founded in 1963, is the largest panda reserve in China. It has an area of 200,000 hectares and is world-renowned as the home for pandas.