Another Pregnant Pause for Panda Fans

The Panda Watch is on again at the National Zoo.

Zoo officials said yesterday that a recent hormone spike detected in the urine of giant panda Mei Xiang may be a sign that she is pregnant again.

Or not.

Mei Xiang was artificially inseminated in March with semen from the zoo's male panda, Tian Tian, a procedure that in 2005 led to the birth of Tai Shan.

The rise in progestin is a good sign, zoo officials said, and may indicate that a fertilized egg is implanting itself in her uterus.

But it is also impossible to interpret with any certainty.

Female pandas often have "pseudo-pregnancies" in which their short breeding period is followed by physical, hormonal and behavioral changes that mimic the real thing.

Panda fetuses are small and develop quickly in the weeks before birth, making a pregnancy difficult to confirm. In the days before Tai Shan's birth, zoo officials still were not certain that Mei Xiang was pregnant because she had stopped submitting to ultrasounds.

Given Mei Xiang's string of pseudo-pregnancies -- in 2002, 2003, 2004 and 2007 (the zoo did not inseminate her in 2006) -- the track record is not good. She has been having weekly ultrasounds since the insemination, and so far there is no evidence of a fetus, the zoo said in a news release.

Physical evidence would not necessarily be expected at this point, and zoo officials say it will be mid- to late July before the mystery is resolved.

By then, Mei Xiang would have given birth -- in time for an Olympic debut.