The birthday party will be private. Kate is thought to be with her husband William at their home in north Wales where the Duke works as an RAF Search and Rescue helicopter pilot. Or she might spend the day at her parents' house in Bucklebury, Berkshire.
The mother-to-be Kate, who is thought to be around 12 weeks pregnant, keeps a low profile of late. She was hospitalised in December with a form of acute morning sickness, called hyperemesis gravidarum, and is limiting her public engagements.
Kate was born at the Royal Berkshire Hospital in Reading, on January 9, 1982.
Prince William, 30, and the Duchess of Cambridge Kate are expecting their first child in June or July 2013.
Voice of Russia, Mirror, the Huffington Post