The Queen's granddaughter couldn't make it to hospital in time for the arrival of son Lucas.

Mike Tindall has spoken about the dramatic arrival of baby son Lucas on March 21, revealing that wife Zara (granddaughter of the Queen) gave birth to their third child on their bathroom floor.

"Arrived very quickly. Didn't make it to hospital. On the bathroom floor," he said on The Good, The Bad & The Rugb?y? podcast. "So yeah, it was running to the gym, get a mat, get into the bathroom, get the mat on the floor, towels down, brace, brace, brace."

A rapid labour is not uncommon mothers who've given birth before, says midwife and founder of hypnobirthing and pregnancy yoga company GlowMummy Sharon Salvage: "When it's your second or third baby, particularly when you've had a long labour the first time, your body has done it all before, and it can happen really quickly."

So, what do you need to know if you're a mum or partner expecting a baby - or you happen to be on hand when someone goes into labour? Here, midwives explain what you should do in the event of an unexpected arrival.

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Call an ambulance

"To be honest, most babies are born in really good condition if they're born that quickly, but you just don't know," Salvage says.

"The first thing to do is if you feel you can't make it to hospital, then you need to make sure you've phoned an ambulance and that someone's on their way to you, with a midwife as well."

Keep calm and listen to mum

"It's important for women to listen to what their body needs when giving birth. I find that instinct kicks in quickly and they often automatically kneel or get on all fours," says Lesley Gilchrist, registered midwife and co-founder of My Expert Midwife.

"A lot of women will naturally put their head a little bit lower than their bottoms, they're literally working against gravity, and it just slows down that process and helps you start to really calm yourself," Salvage says.

She recommends "breathing your baby out" slowly: "You don't need to start doing massive big pushes or anything like that, it's less likely that way that you'll get tears."

Get ready to catch the baby

"This can be anyone with a reliable pair of hands," says Gilchrist. Salvage adds that bathroom births are common, as mothers naturally seek out an enclosed space to feel safer: "Your partner might need to make sure they are able to support baby's head and body so they don't literally flop on the floor."

Skin-to-skin contact

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"Skin-to-skin contact with mum is the best place for babies to be as soon as they are born. This will help to regulate their breathing and keep them warm," Gilchrist says.

"If your baby isn't breathing, while you wait for assistance, I would recommend rubbing your baby with a cloth or towel to stimulate them. Most babies will breathe spontaneously within one minute of birth, however, it is always best to be prepared, just in case."

Then you should keep mum and baby warm by covering them with a warm towel, blanket or anything else you've got to hand.

Don't cut the cord

This is one part of labour that should definitely be left to the professionals.

Gilchrist says: "As long as the umbilical cord is left, the baby will receive oxygen into their blood to help them transition into the world. Never cut or tie the cord until a medical professional arrives."