William, grandson of Queen Elizabeth and second-in-line to the throne, announced last month that Kate was expecting a second baby to join Prince George who was born in July last year, but no date for the birth was disclosed at the time.
The statement from William's office also confirmed that Kate is still suffering from Hyperemesis Gravidarum, acute morning sickness which causes severe nausea and vomiting and requires supplementary hydration and nutrients.
The condition has caused her to cancel a number of official engagements. REUTERS