Oops.

Zoo Atlanta is going to have to rearrange its pronouns again.

Those twin panda boys, Mei Lun and Mei Huan, have turned out to be twin panda girls.

Deputy director Dwight Lawson and associate veterinarian Sam Rivera revealed the news at a press conference Friday morning.

It’s notoriously difficult to figure out the gender of giant pandas, and panda watchers remember that a similar mix-up happened with the twins’ older sibling Mei Lan, 7, who was thought to be a female until Mother Nature made the truth obvious at age 3. The genders of the twins were determined with blood tests, rather than physical examinations, which are difficult and unreliable.

“They are covered up in fur, and you really can’t look and they don’t want you to look,” Lawson said.

Oh, by the way, brother Po also happens to be female. Older brother Xi Lan is, at latest report, still a boy. “So most of our boys are now girls,” said Lawson, who confessed to a poor record when it comes to determining panda gender. “Our batting average is one out of five.”

Is this “The Crying Game” in reverse? There’s no crying for the conservators at the Chengdu Research Base of Giant Panda Breeding in the Sichuan province of China, who are rejoicing that there are more potential panda moms in Atlanta.

All the giant pandas at Zoo Atlanta are the property of the Chinese facility. Xi Lan, 5, and Po, 3, were scheduled to be transferred to China this fall, when veterinarians determined they weren’t quite heavy enough to make the trip in good health.

“We wanted them to be fat and sassy,” Lawson said. The zoo staff decided to postpone that trip until early next year. It was during the preparatory medical exams that Po was discovered to be a female. “We tried to confirm Po without anesthesia, but it is very difficult, and not safe for us,” Rivera said.

A blood test revealed the truth. Veterinarians also decided to test the twins at the same time, and were able to retrieve blood samples without any anesthesia.

Lawson said none of the pandas’ names will change, and neither will any other aspect of their care. But in the future, the zoo will probably use blood tests to determine the gender of its panda cubs, and will probably do so at an earlier age. At 16 and 15 pounds, Mei Huan and Mei Lun are gaining strength and wandering around on exhibit.

Exhibit space will be tight for a while, since pandas are solitary animals and the older siblings and dad Yang Yang are being kept in separate enclosures.

A five-year permit to keep Yang Yang and his bride Lun Lun at Zoo Atlanta elapses in 2014, and the zoo plans to negotiate to keep the pair another five years.