What caused Kate to go into labour?

A general view of the press pen outside the Lindo Wing of St Mary's hospital in London. Image: Yui Mok, PA Wire

Whether it was the full moon, an electrical storm or just conventional 'Baby Mean Time', there are already numerous theories as to what caused the Duchess of Cambridge to go into labour.

Some believe Kate's labour was influenced by the lunar cycle and the arrival of a full moon.

The suggestion is that the moon's gravitational pull affects the amniotic fluid in the same way it affects the water in the sea and rivers.

Maternity wards are said to be busier during a full moon, although there is debate in the medical world about whether the moon does encourage women to go into labour.

Mervi Jokinen, of the Royal College of Midwives, said midwives often talk of how the full moon makes for a busy spate of deliveries.

"It's always sort of been an old wives tale saying that the full moon brings women into labour. Midwives usually do say 'I'm on call. It's a full moon. I'll be busy tonight'," she said.

"There was a study about 20 years ago at a hospital near the River Thames which is a tidal river and it showed that on the full moon they did have more births.

"The idea is that because the baby is surrounded by water, the time of the full moon and the high tide causes the waters to break.

"But there's not enough scientific evidence to show it's proven."

Birth doula Zara de Candole, of Doula UK, said: "As a doula (birth coach) who has supported many women in labour, there does seem to be some link between labour kick starting and a full moon."

There are also suggestions electrical storms and a drop in barometric pressure can bring on labour.

Western central London - near where William and Kate's Kensington Palace apartment is based - experienced isolated heavy rain, thunder and lightning strikes at 6am this morning - just at Kate was admitted to the Lindo wing of St Mary's Hospital in Paddington.

Chris Burton, a forecaster with MeteoGroup, the weather division of the Press Association, said: "The storm affected western central London. There were lightning strikes at around 6am and very localised, intense heavy rain and thunder.

"We've had high pressure with the sunshine but now there's low pressure and it's hot and humid which can cause thunder storms."

Mervi Jokinen said she had not seen a connection between labour and electrical storms.

"We are full of electrolytes but I don't know. it's not something we've discussed as a midwific community. I can't vouch for that," she said.

She added that babies also arrived to their own agenda and their own time scale and put in an appearance when they are ready.

"Nature has its own way of preparing for labour. Before the baby comes, the body need to do some preparations and that's very important," she said.

Pat Wood, who was a midwife for 20 years and has been a doula for two years, said an electrical storm can act as the "tipping point" in sending women into labour.

"It's not going to put everybody into labour but I think it's one of those tipping points for some women," she said.

"There's a pressure around the baby in the uterus. There's change from a high atmosphere to a suddenly low one when a storm comes and the difference in that pressure is what the uterus is trying to equal so your waters can break.

"I very much doubt there's official figures - it's more anecdotal. It's only a tipping point but if it's your 'maybe,- maybe not day' it might be the final straw that does it."