Suzan Murray, the zoo's chief veterinarian, said the cub was not able to get enough oxygen, leading to liver necrosis, or death of liver cells. Murray also said the cub's lungs were underdeveloped and likely didn't provide enough oxygen to the liver.
The cub was born prematurely in September and was a surprise to keepers at the zoo. The cub, believed to be female, died just a week later. The mother and father, Mei Xiang and Tian Tian, are on loan from China until 2015.
Zoo officials will travel to China this month to discuss whether to swap out one or both pandas for the next breeding season. A decision should be made in November.