Twin pandas have been born at the Smithsonian National Zoo in Washington D.C., and they appear to be healthy.

The zoo’s adult female Mei Xiang gave birth to the twins, the newest additions to the giant panda family at the zoo, according to an ABC News report.

They were born hours apart on Saturday. Although they appear healthy so far, their chances of survival won’t be known until they start walking.

The second-born cub weight 132.4 grams, and the other weighed just 86.3 grams. However, it appeared to be fine.

Veterinarians at the zoo are cautiously optimistic of success. Pandas give birth to twins 50 percent of the time, and its’ the third time a giant panda in the United States has given birth to twins.