Giant Panda Cubs
Mei Xiang gave birth to twins Saturday. Pamela Baker-Masson, Smithsonian's National Zoo

Less than a week after the panda team at the Smithsonian's National Zoo detected a developing fetus in Mei Xiang, the giant panda gave birth to two cubs at the park in Washington, D.C. Mei Xiang was artificially inseminated April 26-27 and began experiencing signs of pregnancy or pseudopregnancy July 20.

The birth of two cubs was surprising, but the team was prepared for such an occasion. It was the third time twin giant panda cubs were born in the United States. While the two cubs are being cared for, you can check in on their well-being via the Panda Cam.

The first panda cub was born at 5:35 p.m. EDT Saturday and the second was born at 10:07 p.m. EDT. Both weighed less than a pound at birth, but appeared to be healthy.

The panda team initially planned to alternate having one cub spend time with Mei Xiang while the team bottle-fed the other and kept it in an incubator, but the team ran into difficulties over the weekend in keeping to the swapping schedule. The team was able to swap cubs Monday morning.

"The primary goal for the panda team is for both cubs to have the benefit of nursing and spending time with their mother," zoo officials explained in a post Sunday.

Twins are not uncommon for pandas and occur in around 50 percent of pregnancies, the National Zoo said. Two donors were used for Mei Xiang's pregnancy. Future tests will determine whether the father was Hui Hui, a giant panda living at the China Conservation and Research Center for the Giant Panda, or Tian Tian, of the National Zoo.

Mei Xiang has given birth to two other pandas. Tai Shan, born July 9, 2005, is currently in China, while Bao Bao turned 2 years old Sunday.

The panda team will continue to monitor the health of the new cubs, who won't open their eyes until they are 6 to 8 weeks old. The twins will develop black patches in a week and black hair when they turn 2 weeks, the Washington Post reported. By the third week, the cubs may begin to crawl and by 3 months will begin walking and growing teeth.