Carla O'Reilly had always wanted to be the perfect mother. At 26, O'Reilly was in a good marriage and was at home caring for her newborn son in a small Alberta town.

But while all her friends seemed to be adjusting well to their lives as new mothers five years ago, O'Reilly was living behind "a mask" and secretly battling unwanted, intrusive thoughts about hurting her baby.

Describing a world where common household objects triggered flashes or "movies" of violent acts toward her son, O'Reilly suffered in silence for eight months before checking in to the mental health ward of Calgary's Foothills Hospital for specialized treatment of perinatal obsessive-compulsive disorder.

"Some people have OCD about cleaning," O'Reilly said in an interview. "Mine wasn't like that.

"My obsessions were knives, plastic bags, stairs, bathing, bleach — just any of those types of things that could cause harm. I would see flickers of the movies playing in my head ... The kitchen was a very unfriendly place for me."

While most people have heard about postpartum depression, perinatal obsessive-compulsive disorder — or perinatal OCD — is rarely talked about, even though a 2006 scientific review found as high as four per cent of mothers suffered from it.

The disorder is characterized by repetitive unwanted thoughts, images and impulses the mother recognizes as abnormal, but has no intention of acting upon.

It can begin in pregnancy or after birth and can strike those who've never been diagnosed with a mental illness before.

Diagnosis hard because women don't talk about it

Part of the reason perinatal OCD often flies under the radar is because women are reluctant to talk about the problem, said psychiatrist Marie-Josée Poulin.

"One of the major things I'm telling [health-care workers] ... is that they should forget the stigmas and taboos and also understand that a woman having this disorder won't speak up easily by herself," said Poulin, a professor in the psychiatry department at the faculty of medicine at Laval University in Quebec City.

She is also director of the perinatal psychiatry unit at Quebec City's Centre hospitalier Robert-Giffard, which caters exclusively to women during pregnancy and up to two years after they give birth.

The good news, according to Poulin, is that women tend to respond very well to a combination of medication and counselling and are highly motivated to get better for the sake of their children.

Mom channels despair into advocacy

For O'Reilly, the journey from a very dark place in which she contemplated suicide has evolved into a role as an advocate.

In November she and two other mothers published The Smiling Mask, a book that chronicles their experiences with perinatal mental illness. She also helped set up a postpartum support group in Moose Jaw, Sask., where she now lives.

Her son is now five years old and O'Reilly is no longer battling OCD on a daily basis, although she still has the occasional intrusive thought.

"It's a delicate balance," she said. "But now I know it's just a thought."

The turning point in her own recovery was meeting other women who'd been through the same experience. Now she and her two co-authors are on a mission to educate the public about lesser-known disorders like OCD.

They also want more to be done during pregnancy to screen for women who are at higher risk.

"We've been trying and trying and trying to get the word out there and it's coming slowly," O'Reilly said.

"We just really want women to know you don't have to be ashamed and that's the whole thing with the mask.

"You've got to take off the mask."