It was the worst backache of Josephine Anglin's life. And the best surprise.

Hours after the Nanaimo, B.C., woman went into emergency in extreme pain last fall, doctors removed an eight pound, 14 ounce growth from her body: her name is Neveah.

"It was quite a shocker," says Anglin.

"It took me and my fiancé quite the adjustment to get used to it."

'Cryptic pregnancies'

Call it preg-norant bliss.

It may sound like a dream for women plagued by morning sickness and extreme water retention, but by some estimates as many as one in 2,500 mothers experience so-called "cryptic pregnancies."

Anglin says she can sympathize with the state of shock Ada Guan found herself in after delivering an unexpected baby on an Air Canada flight to Japan on the weekend, as she also gave birth without ever knowing she was pregnant.

Baby Chloe, who was born on an Air Canada flight to Japan, arrived as a complete surprise. (Facebook)

"It's amazing how you can go from working every single day and not knowing you're pregnant," Anglin says.

"And then all of a sudden, you're on maternity leave, you have a baby. It's quite a shift."

Vancouver obstetrician Dr. Shelley Ross says that in more than three decades of practice she can count on one hand the number of people who didn't know they were pregnant until shortly before giving birth.

"It's pretty rare," she says. "It's pretty hard to deny a large mass in the front of your abdomen."

Some women do have very irregular periods, and obesity can mask weight gain, but Ross says most patients tend to have an inkling something is up in the baby department.

The phenomenon of unexpected birth has caused debate among researchers.

Some studies attribute it to a denial of pregnancy, where women ignore the obvious signs of an impending baby for psychological reasons or shame.

But others point to case studies involving women who didn't stop menstruating and gained very little weight.

"I went full term with no idea that I was pregnant," says Anglin, who works at a hardware store.

"I was lifting up concrete bags and heavy stuff that you're not supposed to be lifting."

'A baby in the toilet!'

Totally unexpected births tend to make headlines, not least of all for the unusual places where they happen.

Vancouver's Rachel Suttie went into labour without the benefit of knowing she was pregnant while hiking the West Coast Trail in 2011.

Ada Guan and Wesley Branch welcomed their unexpected daughter Chloe to the world on an international flight. (CBC)

And Ottawa's Kendra Reid delivered a baby boy into a toilet in 2013; she thought she had eaten too much pizza.

"I just heard this enormous sploosh," she told CBC at the time.

"A baby in the toilet! What do you do?"

Anglin says she first learned she was pregnant from the doctors in emergency.

She called her mother, who didn't believe her at first, but then set about trying to make up for nine months' worth of lost baby preparation time. A friend got busy on social media.

"She put out on Facebook saying, 'I have a family friend who was pregnant, had no idea, she has nothing,'" she says.

"My whole living room was jam-packed full of baby stuff."

Oh baby! Now what?

Beyond the novelty factor, giving birth without any preparation for what comes after can be traumatic, which is why one U.S. woman started a support group for cryptic pregnancies.

Anglin says Guan and her husband should be prepared for skepticism and the negativity that inevitably follows media exposure.

"I did get a little bit of a downside," she says.

People sniped about her weight, her intelligence and her story.

"So it was really hard to read those comments and everything, but then I look at her baby and I'm in love. I wouldn't change it for the world."

Still, a bit more prep time might have been nice.