The newest panda at the National Zoo left the world scarcely a week after entering it, forever nameless.

Zookeepers rushed to retrieve the panda cub Sunday morning after mother panda Mei Xiang keened in distress. CPR and other life-saving measures were attempted, but proved unsuccessful.

Preliminary results from the necropsy of the baby panda don’t as yet point to a clear cause of death. The cub seems to be a female, weighing less than four ounces. She bore no signs of external or internal trauma, so she was not inadvertently crushed by her mother. Milk residue in the cub’s gastrointestinal tract confirmed that she was nursing.

Thus far, the only abnormalities found by the veterinarians are some odd fluid in the cub’s abdomen and a slightly abnormal liver.

“They don’t know yet whether either of those things is significant, and they’re still investigating,” the zoo said in a statement Monday.

Mei Xiang, meanwhile, seems to be bearing up as best she can – eating and drinking a little. Keepers did notice that, after the cub’s death, she was cradling an object, according to the zoo.

“We will learn from this tragedy and hope we will gain a better understanding of giant panda reproduction and cub health as a result,” the zoo said.

Panda cub deaths in captivity are, sadly, not unusual. Just this past July, a baby giant panda born in a Tokyo zoo died after likely choking on breast milk while nursing.

Mei Xiang’s ability to conceive after being artificially inseminated in April was not pegged as likely – experts gave her about a 10 percent chance of becoming pregnant. The latest tragedy caps off a long streak of false starts for Washington’s panda mother -- Mei Xiang showed signs of pregnancy five times since 2007, but they all turned out to be false alarms.

The deceased cub was her second with the male Tian Tian. The panda couple's first offspring, a male named Tai Shan, was born in 2005 and currently resides at a panda breeding facility in China.