She gave birth to twins. This is the oldest panda to debut as a mother

On Thursday, a panda named Ying Ying gave birth to twins. The cubs were born one day before her mother's 19th birthday. If Ying Ying were a human, she would have turned 57. The male and female panda cubs are currently “in a very delicate stage and need time to stabilize,” caretakers at Ocean Park Hong Kong said in a statement. “Please wait patiently for a few months until they make their debut and can officially meet everyone!” the zoo said in a statement, adding that the cubs are in intensive care around the clock. A zoo official told the BBC that the female appears more fragile because she has a lower temperature, her squeals are quieter than her brother's and she is eating less.

The twins were in labor for five hours, during which Ying Ying lay on the floor, writhing and squirming, Ocean Park Hong Kong officials said.

Giant pandas (Ailuropoda melanoleuca) are pink at birth and fit in the palm of a human hand. These animals are known for having difficulty breeding in captivity. Fertilization is also very rare in the wild, because pandas lead a solitary lifestyle. Females are fertile only once a year, for 1-3 days.

Ying Ying and her male partner, Le Le, who is the father of the twins, were donated to the Hong Kong Zoo by the Chinese government in 2007.

There are about 1,800 wild pandas in the Sichuan Mountains in western China. About 600 of the animals are bred in captivity, some of which Beijing lends abroad. The number of pandas in the wild has been growing in recent years, and they are no longer considered an endangered species, but merely vulnerable.