Catherine - better known to many as Kate Middleton - is not due to give birth until 25th April.
But police, palace, and hospital officials have already begun preparations outside the private Lindo Wing at St Mary’s Hospital, Paddington, in London.
Advanced parking notices have already been posted outside, stating that restrictions will soon come into effect.
And police are now beginning to erect barriers outside the hospital, as well as press pens for journalists, photographers and television crews.
This has been done to stop them from gathering directly outside the hospital wing, as they did at the birth of Prince George.
The new royal baby, rumoured to be a girl, will become fourth-in-line to the throne, relegating Prince Harry to fifth place.
Prince William, 32, and Kate Middleton, 33, have released a statement thanking people for their well wishes.
“They know that people are excited that Prince George will soon have a little brother or sister and it means a great deal to them that so many will be celebrating this important moment for their family,” a Kensington Palace spokesman said.
Not long to go now, everyone!
ROYALS IN RETROSPECT: A LOOK BACK AT PRINCE GEORGE'S FIRST YEAR IN PICTURES: