The Duke and Duchess of Cambridge still don't know the sex of their baby.

Duchess Catherine, due in mid-July, is planning to give birth to their first child naturally at the private Lindo Wing of St. Mary's hospital in London, where both Prince William, who will turn 31 on Friday (21.06.13), and his brother Prince Harry, 28, were born.

Sources said the Duchess, 31, hopes to have her husband, her mother Carole Middleton and her sister Pippa Middleton by her side, but a Palace spokesperson reiterated today (19.06.13) that the couple do not know the sex of the baby, as they want it to be a surprise.

Prince William will be flown or driven to the hospital if he is away when the Duchess goes into labour.

A royal source told the MailOnline website: "He very much plans to be at the birth but between now and then will also be on and off duty in north Wales, meaning he might have to get there rather swiftly."

Once extended family, including Queen Elizabeth, have been notified, a traditional bulletin, signed by the royal medical team, will be posted on a wooden easel on the forecourt of Buckingham Palace to officially announce the baby's birth, shortly before an electronic announcement is made.

The palace spokesperson said: "We wanted to retain some of the theatre of the notice. It is quite important to us that this is done properly and with the degree of dignity that the event demands.

"This is the birth of a child who will be in line to the throne. It is a rare occasion and it is nice to be able to do it with some historical precedence.

"While it is a deeply personal and private event, the Duke and Duchess of Cambridge realise this is a time of national celebration and that there will be vast interest in the baby. They realise many people will want to share in their happiness."

The palace has other "contingencies" in place in case the Duchess happens to be elsewhere when she goes into labour.

The spokesman said that there is "still some discussion" about where the family will be based amid reports she will move in with her parents in Berkshire for six weeks once the Duke returns to work as their new apartment at Kensington Palace is still being renovated.