The BBC said presenter David Attenborough's narration was carefully worded so that it did not mislead audiences.
In the episode, seen by more than eight million people in Britain on November 23, the camera follows a female polar bear in the Arctic as Attenborough comments: "She starts to dig a shallow nest ... once the snow here is deep enough, she'll dig down to make a den. She'll then lie waiting for her cubs to be born as winter sets in."
He then says: "On these side slopes beneath the snow, new lives are beginning."
Footage of the newborn cubs filmed at the German zoo is then screened but Attenborough does not say in the program that the mother and cubs were in fact in a man-made den.
The veteran broadcaster defended the decision to film in the zoo.
He told ITV on Monday: "If you had tried to put a camera in the wild in a polar bear den, she would either have killed the cub or she would have killed the cameraman, one or the other."
He said explaining about the zoo during the show's commentary would have ruined the atmosphere, adding: "It's not falsehood and we don't keep it secret either."
The BBC said it had made it clear the footage was from a zoo in an interview with producer Kathryn Jeffs that was posted on the broadcaster's website a few weeks before the program aired.
In the video, Jeffs says there was no way to film a polar bear giving birth in the wild.
Check out the trailer for Frozen Planet:
- AAP