XI'AN, June 28 -- Eleven-year-old giant panda, Yangyang, has given birth to twin cubs at a breeding center in northwest China's Shaanxi Province this week.

The twins -- a male and female -- were born on Wednesday and weighing 162 grams and 88 grams and are the third and fourth offspring of Yangyang, who had twins in 2009. A worker of the center said giant pandas had twins about 30 percent of the time.

The cubs are being kept in incubators, and are in a stable condition under 24 hour care.

"The mother can only look after one cub, so we only brings one baby at a time to the mom for nursing," said the worker.

Yangyang has been artificially inseminated twice since March. She is fed 20 kilograms of bamboo a day to ensure a plentiful milk supply for her babies.

The giant panda lives mainly in the mountains of China's southwestern province of Sichuan and northwestern provinces Shaanxi and Gansu. They are threatened by habitat loss and a very low birthrate. Only about 1,600 still exist in the wild, and some 300 live in captivity around the world.

Pandas are known for being sexually inactive and cubs are usually born between July and September.