Scientists at the National Zoo in Washington, D.C. have detected rising hormone levels in the zoo's female giant panda, indicating that she could be pregnant.

The rising levels mean Mei Xiang (may-SHONG) could either give birth in 40 to 50 days or come to the end of a false pregnancy. She was artificially inseminated in January.

Reproductive biologist Janine Brown says zookeepers remain "hopeful, but cautious" that Mei Xiang is pregnant. Brown says the panda's hormone levels and behavior sometimes indicate she is pregnant when she's not.

Veterinarians are conducting weekly ultrasounds to look for a fetus. So far they haven't seen any indication of one, but it's still too early. Panda fetuses don't start developing until the last weeks of a gestation period.