The arrival of the overdue royal baby would coincide with the Duke and Duchess of Cambridge's wedding anniversary, if the prince or princess puts in an appearance today.
Unless Kate is admitted to hospital, the couple will celebrate their fourth anniversary privately in a low-key way at Kensington Palace as they eagerly await the birth of their second child.
The Duchess, who said the baby was expected to arrive mid-to-late April, has gone past her expected due date, just as she did with Prince George in 2013.
Fewer than one in 20 women give birth on their due date. On the NHS, induction is offered to women who go two weeks overdue, but Kate is having her baby at the private Lindo Wing.
Royal fans, who have been camped outside the Lindo wing, were treated to a special delivery of pastries from the Cambridges.
Well-wishers believe the royal baby could be a girl, after the parcels arrived wrapped in pink ribbon.