Royal baby: How long is second labour and when is Prince George's sibling expected to arrive?

The Duchess of Cambridge was admitted to St Mary's Hospital's Lindo Wing early this morning

Outside the Lindo Wing where the Duchess of Cambridge is due to give birth (AP)

The Duchess of Cambridge has gone into labour, arriving at St Marys Hospital early this morning – but how long are we going to endure the seemingly endless media updates this time round?

While exact details surrounding the 33-year-old's second labour remain scarce, given that it is the Duchess of Cambridge’s second baby we can expect a faster birth.

How long can we expect to wait?

Second births are traditionally shorter so the signs are positive that the fourth in line may be presented to the world later today.

The average second labour last five hours, and is unlikely to push past 12 hours, according to BabyCentre.co.uk. The couple’s first child, Prince George, was born at 4.24pm on 22 July 2013 after a 10 hour labour.

The Duchess was admitted to the Lindo Wing (where Prince George, her husband Prince William and Prince Harry were a ll born) at around 6.30am. Best bets are for the child to appear sometime this afternoon.

A couple walk past the Lindo Wing at St.Mary's Hospital in north London, Britain, 29 April 2015 (EPA)

Why are second births quicker?

Second (and subsequent) labours tend to be faster because the cervix dilates quicker than in the previous birth.

Are they trickier than first births?

No. Given your body has already done this once, many women – but not all – find birth easier as the vaginal and pelvic floor muscles have already been stretched by birth.

Any predictions on the size of the baby?

There is evidence that second children tend to be larger babies than the first. Prince George was eight pounds six ounces when he was born, but second babies are (on average) only five ounces heavier.