Atlanta Zoo officials said on Friday that twin giant panda cubs, the first to be born and survive in the United States, have both turned out to be female.

The zoo, which initially had identified both cubs as male after they were born in July, said DNA testing had now shown they are both female.

"Prior to the time they are at least 3 years old, there are no obvious external cues as to their sex," the zoo said in a statement.

Members of the public this fall helped choose the twins' names, Mei Lun and Mei Huan, which come from a Chinese idiom meaning "something indescribably beautiful and magnificent."

The DNA tests showed a third panda, 3-year-old Po also initially believed to be male, is female as well.

Po and the twin cubs were conceived through artificial insemination with the same set of parents.

Giant pandas are endangered and live only in a few mountain ranges in central China. An estimated 1,600 live in the wild and about 300 in captivity, mostly in China, zoo officials said.