Prince William's wife, Kate, in hospital in labour

Bookmakers predict the baby will be a girl.

Prince William’s wife, Kate, has gone into labour and has been admitted in hospital for the birth of the couple’s first child, who will be third in line to the British throne, the prince’s office said on Monday.

After weeks of feverish media speculation over the arrival of the royal baby, Kate, 31, was taken early on Monday to the private wing of St Mary’s Hospital in Paddington, West London, where William was born in 1982.

“The duchess travelled by car from Kensington Palace to the Lindo Wing at St. Mary’s Hospital with the Duke of Cambridge,’’ Kensington Palace said in a statement.

“Things are progressing as normal. It wasn’t an emergency,’’ the statement said.

Royal sources said Kate had planned a natural birth with William, a Royal Air Force search and rescue helicopter pilot, to be at her side.

The sex of the baby, who will be third in line to the throne behind Grandfather, Prince Charles, and father, William, is unknown as the royal couple wants it to be a surprise.

Bookmakers have a girl as the firm favourite.

Newspapers have speculated that Kate’s sister, Pippa, and mother, Carole Middleton, might be present for the birth, while Queen Elizabeth will be among the first to be informed of the arrival.

The baby will be delivered by Marcus Setchell, the queen’s former gynaecologist.

Kate, who needed hospital treatment after suffering acute morning sickness in the early part of the pregnancy, made her last public appearance on June 15 at the “Trooping the Colour’’, a military ceremony to mark Queen Elizabeth’s official birthday.

The BBC reported she entered the hospital though a back door and avoided the crowd of media from around the world who have camped outside the hospital since July 1.

The Lindo Wing, where maternity rooms cost from $7,800 for a one-night stay, is where the late Princess Diana gave birth to William, 31, and his younger brother, Harry, who will drop a place in the line of succession after the arrival.

The birth will be announced in the traditional way, with an envelope containing notice of the baby’s details taken from the hospital to the queen’s London residence, Buckingham Palace, where the news will be posted on a board outside the main gates.

“It’s a lovely idea they are going to have an envelope rushed over to Buckingham Palace and the figure crossing the forecourt with the easel and putting up the announcement,’’ royal historian, Hugo Vickers, told Reuters.

“I think that’s absolutely great, it’s rather theatrical. I think we’ll all enjoy that hugely.’’

While the baby’s sex is not known, there has been much conjecture that the child will be a girl after the duchess accepted a teddy from a well-wisher in March saying: “Thank you, I’ll take this for my d.’’

Whether a boy or a girl, the baby is destined to one day be a monarch after Britain and other Commonwealth countries that have the queen as their monarch agreed to change the rules of royal succession so males no longer have precedence as heir.

Royal officials have confirmed the baby will be known as His or Her Highness Prince or Princess (name) of Cambridge.

Since William and Kate’s wedding, the April 2011 the couple has officially been known as the Duke and Duchess of Cambridge.

Bookmakers have Alexandra as the clear favourite for the baby’s name, followed by Charlotte and Diana, in honour of William’s mother who died in a Paris car crash in 1997.

George is the favourite boy’s name followed by James.

However, it might take some time for the name to emerge. The announcement of William’s name took more than a week.