Veterinarians at the Smithsonian's zoo said last week's urinary progestin test indicates it might yet be a month before Mei Xiang gives birth to a cub or comes to the end of a false pregnancy, which is common in giant pandas.

Zoo scientists artificially inseminated Mei Xiang with semen from the zoo's male giant panda Tian Tian in March and, since then, have conducted weekly hormonal analyses on daily urine samples from Mei Xiang. Zoo veterinarians are also conducting weekly ultrasounds on Mei Xiang to monitor any changes in her reproductive tract and look for evidence of a fetus. So far, they have not seen evidence of one, although panda fetuses don't start developing until the last weeks of a gestation period.

This is the sixth year the National Zoo has tried to breed the giant pandas. Mei Xiang had pseudopregnancies in 2002, 2003, 2004 and 2007. She gave birth to a cub in 2005 and did not reproduce in 2006.