A Chinese panda at the Memphis Zoo is definitely pregnant, officials there said.
Ya Ya, a giant panda, was artificially inseminated in January after she and a male companion failed at mating. Since then, the zoo has closely monitored her as the potential due date drew near for the 6-year-old panda.
"I'm excited, but I'm also cautious because we have a long way to go before the birth," said Chuck Brady, the zoo's president.
Ya Ya is expected to give birth in the next 30 to 45 days, and the zoo will do weekly ultrasounds to monitor the health and growth of the fetus, zoo spokeswoman Julie Dodson said.
Zoo staff members now monitor Ya Ya 24 hours a day. She is in her maternity den and has access to a day room where zoo visitors can see her.
As the due date approaches, Ya Ya will likely settle into a tree in her maternity den that is a replica of where a giant panda would give birth in the wild, zoo officials say.
Panda pregnancies cannot be confirmed until shortly before the delivery date. Gestation lasts about 133 days.
An ultrasound showed that Ya Ya's fetus recently began growing, The Commercial Appeal newspaper reported.
Zoo officials have been watching Ya Ya this month for behavioral changes such as pacing, agitation and becoming more secluded.
"This is a critical stage, and we'll have to monitor Ya Ya carefully," Brady said.
Ya Ya and a male panda, 8-year-old Le Le, are on loan from China. Ya Ya and the cub will be off exhibit for about three months, zoo officials say.
Pandas are notoriously poor breeders - one reason their species is endangered - and females have only three days a year in which they can conceive.
Only three other U.S. zoos - those in San Diego, Washington and Atlanta - have giant pandas. The most recent panda cub born in the U.S. was Mei Lan in Atlanta last September.