The Duke and Duchess of Cambridge's baby is due in July, St James's Palace confirmed.
It was announced that Kate and William were expecting their first child in early December.
The announcement was made less than 12 weeks into the pregnancy after Kate was admitted to the King Edward VII Hospital in central London suffering with Hyperemesis Gravidarum - a severe form of morning sickness.
Kate condition is continuing to improve following the stay in hospital, a spokesman for the couple said.
Kate was last seen in public last Friday when she visited the National Portrait Gallery in London with William for the unveiling of her first official portrait.
She looked well and smiled during the brief appearance, with some commentators spotting the start of a slight baby bump.