Polar Bear Knut - the sibling sequel?

Knut, the Berlin Zoo's well-known polar bear, may soon have as many as three little siblings before Christmas, the zoo's veterinarian said Friday.

Knut's mother, Tosca, and the zoo's two other female polar bears, Katjuscha and Nancy, may all be pregnant after mating earlier this year with Knut's father, Lars, and could give birth before the end of December, according to veterinarian Andre Schuele.

But polar bear pregnancies are hard to detect and to track. Tests like those humans use do not work, and polar bear embryos are so small the mothers do not grow big tummies.

The zoo is hopeful enough, however, to have built three special caves for the female polar bears to use to give birth.