Three weeks after Chelsea Elker gave birth to her second baby, she was overwhelmed by a thought that also felt something like an urge: What if she smothered him?

Elker, who was peacefully nursing at the time, had never experienced anything like that when her eldest was born, and was horrified.

From that night on, however, the disturbing thoughts kept coming.

As she buckled her newborn into his car seat, Elker worried: “What if I touch him inappropriately?” As she washed dishes she’d think: “What if I stabbed him?” Elker reassured herself that of course she would never hurt her baby, only to immediately question why, then, she’d even entertain such ideas in the first place.

“It’s hard to explain,” Elker, now 29 and a mother of three, told HuffPost. “I felt like, ‘If I’m thinking it, it obviously means I want to do these things.’”

In the last decade, awareness about postpartum depression has exploded as research has revealed it affects anywhere between 10 and 20 percent of moms. Likewise, knowledge about postpartum anxiety — which could affect up to 17 percent of new moms, according to some estimates — has also begun to spread among women and health care providers. Mothers struggling with anxiety and depression now at least have some kind of name and explanation for the things they are feeling.

For the smaller subset of mothers who have postpartum obsessive compulsive disorder, that kind of broad — or even broadening — recognition of their circumstances simply does not exist. “OCD” has become a watered-down term, an acronym thrown around in conversations about that friend who’s just a bit too fastidious or who is especially germaphobic.

But for mothers tormented by the condition, it signifies something much darker — a cycle of fears and behaviors that grabs hold of them and threatens to upend their sense of who they are in one of the most grueling, vulnerable moments of their lives. And many find it impossible to open up, gripped by fears that someone will take their baby away.

“It became 100 percent of my day and 100 percent of my nights,” Elker said. “I could be having a conversation with you and inside I’m thinking 1,000 different, terrible things.”

Inescapable ‘Intrusive Thoughts’

In many ways, OCD — perinatal or otherwise — is simple to identify. Its signature symptoms are intrusive thoughts and fears (i.e. “obsessions”) and often rituals (“compulsions”) aimed at making those thoughts disappear.

Under the DSM-5 — the most recent version of the “bible” of psychiatry — OCD was given its own chapter and moved out from under the broader umbrella of anxiety disorders. There is no diagnostic distinction between OCD that begins during the postpartum period and at other times in a person’s life, though women who have experienced anxiety and OCD in the past are at higher risk of dealing with it again postpartum.

In new moms with OCD, however, the intrusive thoughts that are a hallmark of the disorder tend to center around one thing: their babies. Suddenly, a woman who longed for motherhood may be utterly convinced that something or someone — perhaps even herself — is going to hurt her child in ways she’d never considered before, either deliberately or through carelessness.

“I had a patient who presented at five or six weeks postpartum with her fourth baby, and she had a precipitous onset belief that she couldn’t be near knives,” Dr. Catherine Birndorf, co-founder of The Motherhood Center of New York, a clinic that specializes in perinatal mood disorders, told HuffPost. “She couldn’t be in the kitchen. She had visions of taking a knife and cutting her infant’s throat — and she was absolutely freaked out by these intrusive, violent images. That’s super common in perinatal OCD.”

Moms who experience those thoughts are almost immediately overcome by shame and horror, which is the primary way experts distinguish between OCD and postpartum psychosis, a rare, severe psychiatric emergency in which new moms can absolutely pose a threat to themselves and their babies.

“OCD is what we call ‘egodystonic’ in so much as it is upsetting and exhausting to have the thoughts and do the actions you do to try and make yourself feel better,” Birndorf explained. In postpartum psychosis, delusions and hallucinations take over.

Loretta Notareschi, 40, gave birth to her daughter in 2013 and had her first intrusive thoughts — about throwing her down the spiral staircase in her home— while she and her baby were recovering in the hospital. It wasn’t a hallucination or a desire, but it gripped her imagination nonetheless. She told a nurse who reassured her that she was probably just exhausted, but before she was discharged she had to meet with a social worker.

“I was triggered by all kinds of things, especially the spiral staircase or knives,” Notareschi told HuffPost. “Bathtubs. Being in the car. I would think, ‘What if I hurt her with that?’ Or, ‘What if I hurt myself with that?’”

Over time, she began to develop what she thought of as coping mechanisms, though later she learned they were simply the hallmark compulsions of her illness.

“To the OCD mind, they seem like brilliant ways to deal with your anxiety,” Notareschi said, laughing ruefully. “I decided in the first couple of days after my daughter was born that every time I had a scary thought I would have to repeat to myself a certain phrase, which was ‘Baby face, hairbrush, duckie.’ In my mind, it was going to neutralize the thought or magically make it OK.”

An Adaptive Behavior … Gone Wrong?

Interestingly, research suggests that some elements of postpartum OCD may be adaptive. A 2013 study of roughly 400 women found that 11 percent of new moms were experiencing some obsessive-compulsive symptoms two weeks after giving birth. Six months later, nearly half of those women still had symptoms, while another 5 percent of moms had developed symptoms at that point.

That study asked if women were having any symptoms of OCD, not if they met the criteria for an actual diagnosis. But it raises the possibility that the prevalence of the disorder is much higher than the 2 percent that is often cited — and raises tricky questions about what’s normal (and what is not) in the minds of new mothers faced with the daunting task of keeping a helpless newborn alive.

“One of the most common obsessions is fear about germs, and some of the most common compulsions are checking behaviors and washing behaviors,” Dr. Dana Gossett, a professor of obstetrics and gynecology at the University of San Francisco California and the author of that 2013 study, told HuffPost.

“It’s not crazy to think that if a woman has a newborn, she might want the house to be clean and for people’s hands to be clean,” she continued. “It’s not unreasonable that she would want to check on her baby frequently to make sure he or she is OK. What happens in OCD is that is carried to a point where it is no longer logical or productive.”

And when those thoughts become intrusive and frightening, mothers become understandably fearful to come forward to share what they’re going through — and to be counted.

“We know depression is common. It’s well studied and there’s a lot less stigma now than there was 15 years ago around articulating feelings of sadness,” Gossett said. “Whereas if a mom says, ‘I’m terrified I’m going to burn down the house’ or ‘I’m terrified I’m going to shake my baby to death,’ there’s so much more shame and fear.”

And it is not unreasonable for women to worry that their babies could be taken from them, she added.

“One of the challenges about OCD is that it is less broadly known, so even OBs and pediatricians who are good about screening for depression are going to be less familiar and less comfortable with these diagnoses — and how to make that distinction between psychosis — so women get the help they need,” Gossett said. Postpartum Support International, an advocacy and education group, says that postpartum OCD is the most misunderstood and most commonly misdiagnosed of the perinatal mood disorders.

That is what makes postpartum OCD so heartbreaking. Like so many other mental health issues that crop up during the tumultuous postpartum period, experts say it is highly treatable with some combination of therapy, support, medication and time. But in a culture that demands moms cherish every exhausting moment of raising young children, admitting to frightening obsessions can feel impossible.

“I didn’t want to tell anyone, because all the media tells you with stories about women who hurt their babies is that if you think a thought, you want to act on it,” said Elker, who took more than a year to recover from postpartum OCD through a combination of intensive therapy and medication and has written extensively about her experience.

“But I didn’t want to hurt them,” she said. “I was so fiercely trying to protect them that I drove myself insane.”