Still, there was hope.
Laurie Thompson, one of the about half a dozen panda keepers at the zoo, said each of the keepers gave Mei Xiang a pep talk.
"I know you can do this. You need to prove them wrong. You need to have a baby this year," she said she told Mei Xiang, who she has worked with since 2000.
Thompson said she got a telephone call Sunday night from another keeper. "I think I hear a panda cub," the keeper said. A small group then got on their computers to watch the zoo's panda cam. Sure enough, there was the unmistakable bird-like screech of a cub.
For now, keepers said, Mei Xiang is doing well and responding to the cub's fussy grunt and high-pitched squeal. So far, there have only been fleeting glances of the cub and it's not clear what sex it is. But keepers will continue to watch the two on camera, the same view the public has online, and won't step in unless necessary.
Keepers will likely do their first exam in three to four weeks, and it will be several months before the public can see the cub in person.
Zoo director Dennis Kelly said officials expect the newborn will bring an additional 250,000 to 500,000 visitors to the zoo over the next year. That's on top of the 2 million visitors the zoo already receives annually.
Under an agreement with the Chinese government, zoo officials can keep the cub for four years before it has to go back to China, just as its older brother Tai Shan did in 2010.
Still, there's some danger for the cub, especially in the next two weeks. Pandas have accidentally crushed their small cubs. And the zoo's first panda couple, Ling-Ling and Hsing-Hsing, had five cubs, but none of them survived more than a few days.