Bookmakers Coral marked an upsurge in Royal baby bets on Tuesday morning by projecting the latest odds on the baby's gender onto Buckingham Palace and tweeting a picture to the official British monarchy account.
A baby girl is odds on at 1/2 but the odds on a boy have been slashed to 6/4 from 15/8.
Coral spokeswoman Nicola McGeady said: "Speculation over the sex of the royal baby has been rife over the last couple of months and as the due date approaches, opinions are changing.
"A few months ago Kate hinted at a girl and punters queued up to back a female heir, but since a spokesperson for the royal family announced that they don't know the sex, it's become a level playing field and plenty of punters have backed a boy."
The bookies is offering odds on baby names including Alexandra, Charlotte, Diana, Elizabeth, Victoria, George, Louis and Phillip, and is taking bets of the baby's date of birth, weight and even hair colour.