There have been weeks of anticipation over the forthcoming birth of the Duke and Duchess of Cambridge's child. But here are 10 of the lesser-known facts about royal births.
1. Home secretaries used to attend royal births. The last time was in 1936 for the birth of the Queen's cousin, Princess Alexandra. The custom was ended in 1948 ahead of the birth of Prince Charles. At the time Home Office researchers could find no evidence for the belief that the home secretary's presence was anything to do with verification, according to a biography of the Queen written by Ben Pimlott.
Then Home Secretary Sir William Joynson-Hicks was present at the Queen's birth in 1926, despite the government being embroiled in a row with coal miners. He was reported to have conveyed the news by special messenger to the Lord Mayor of London.
2. The Archbishop of Canterbury also won't attend the birth, as was the custom in the past. One exception was in 1841 for the birth of Queen Victoria's first son Albert Edward in 1841 when the archbishop and two companions - Lord Wharncliffe, Lord President of the Council, and Lord Stanley, Secretary of the State for the Colonies - turned up late and missed the birth. The Times does not record whether heavy carriage traffic was to blame. The Bishop of London did make it.
3. There were reportedly 42 eminent public figures called in to verify the birth of King James II's son James Francis Edward in 1688 at St James's Palace, in what visiting Cambridge University scholar Prof Mary Fissell describes as "the first media circus surrounding a royal birth". People doubted that the King's wife Mary of Modena was genuinely pregnant and, once she went into labour, Fissell says, there were rumours spread by cheap broadsheets and in coffee houses that the baby who emerged had been smuggled into the bedchamber in a warming pan, or that it had been sneaked into the bed through a secret door in the bedhead.
That scandal put a permanent question mark against the baby's legitimacy, Fissell says, and he never became king. William of Orange and his wife Mary went on to seize the throne in 1688 in what came to be known as the Glorious Revolution.
4. The birth of Princess Margaret in 1930 caused some difficulty for then Home Secretary JR Clynes. He had remained in Scotland while he waited to witness the birth of the princess at Glamis Castle which ended up happening two weeks later than planned, says royal historian Hugo Vickers. When the baby was finally on its way, Clynes was already ready for bed, but on the news of the impending arrival had to scramble to the castle for the birth.
5. A surname will not necessarily be required, as the new baby will have the title HRH Prince or Princess and will be referred to in this way. However, if Catherine and William want to include a surname, there are three choices available - Mountbatten-Windsor, Wales or Cambridge. In 1917 George V adopted Windsor - after the castle of the same name - as the "surname" of his family, changing it from Saxe-Coburg and Gotha as a result of anti-German feeling during World War I. The Queen and Prince Phillip combined their surnames to make Mountbatten-Windsor - their direct descendants can use this name but it isn't binding. In his military role, William uses the name of his royal house - Wales - which is taken from his father. Similarly Cambridge, the title given to the couple when they married, could be used.
6. The news will come on an easel. It's custom for news of royal births and deaths to be attached to the railings of Buckingham Palace. In this case, it will be displayed on an ornate easel in the forecourt of the palace. The Queen, senior members of the royal family, and the Middleton family - if they are not at the hospital - will be told about the birth first. Then a royal aide will hurry from the hospital to the palace under police escort with a bulletin. The foolscap-sized note, bearing the Buckingham Palace letterhead and signed by key medical staff, will be the nation's first chance to find out if it is a boy or a girl. After the note is displayed, an announcement will be posted on Twitter and Facebook, and the media will be informed.
7. Prince William is following modern convention by taking paternity leave. He is expected to take the two weeks' paid leave offered by the Ministry of Defence. He will then return to his job as an RAF search and rescue pilot. Of course, statutory paternity leave has only been in force in the UK since 2003. Prince Phillip was playing squash when Charles was born.
8. Royal births are usually celebrated with a 41-gun salute by the King's Troop Royal Horse Artillery. The basic royal salute is 21 rounds, but because it will be conducted in Green Park, a royal park, an extra 20 rounds are fired. At the Tower of London, 62 rounds will be fired - the basic 21, 20 because the Tower is a Royal Palace and 21 for the "city of London". Union jacks will also be flown from all Government buildings, Royal Naval ships, and defence establishments.
9. The birth is in a hospital. While it might seem obvious that the Duke and Duchess of Cambridge's baby would be born in a hospital, Prince William was actually the first future king to arrive in such a way. Both he and his brother Prince Harry were born in the private Lindo Wing of St Mary's Hospital in Paddington, west London, where the duchess is giving birth. The baby will be delivered by Marcus Setchell, gynaecologist to the Royal Household. The Queen was born at a home belonging to her mother's parents at 17 Bruton Street in Mayfair, London. The current heir to the throne, Prince Charles, was born at Buckingham Palace, while his sister Anne was born at Clarence House.
The new parents are likely to present the newborn baby to the world via the press camped outside the hospital. The Queen showed off the royal babies on the balcony at Buckingham Palace in front of huge crowds.
10. The christening robe will be a replica of one that has been used since 1841. It is not yet known where the latest addition to the family will be christened, but Prince William - like his father the Prince of Wales - was christened by the Archbishop of Canterbury in the Music Room at Buckingham Palace. The robe was made for the christening of Queen Victoria's eldest daughter. Made of fine Honiton lace lined with white satin, it has subsequently been used for generations of Royal christenings. The current Queen wore it, her children all wore it and so have all but one of her grandchildren - including Princes William and Harry. In 2008, the Earl and Countess of Wessex's son wore a replica robe designed to preserve the original.