Catherine is an art history graduate and the eldest child of Michael and Carole Middleton, self-made millionaires who run a party-supplies company.
Tabloid speculation about a pregnancy increased in September when Catherine substituted water for wine during a state dinner toast in Singapore.
The buzz reached a boil two weeks ago when Australia's New Idea magazine quoted close friend Jessica Hay saying her former schoolmate, Catherine, would soon announce "wonderful, happy news."
Life & Style magazine in the United States published its own "exclusive" with the same Hay quotes of a December announcement, which she said she had on "the highest authority."
A family history website did the math last summer and predicted Catherine would be with child by November, according to a Time.com report. Genesreunited.co.uk calculated that "the average period between a royal wedding taking place and the couple's child being born is 851 days." Based on that, it predicted a pregnancy in November and a birth on August 27, 2013.