New mums have been warned about the dangers of post-natal depression for years, but new research suggests they are just as susceptible to another mental illness: Obsessive Compulsive Disorder.
A Northwestern University study found that 11 per cent of new mothers develop OCD, as many as those affected by post-natal depression.
Researchers from the Chicago university's medical science team surveyed women at two and six weeks post-partum and found that they were five times more likely to experience OCD symptoms than the general population.
What starts as natural worries about the baby's health and safety can quickly spiral out of control, leaving the mother unable to live a normal life.
"A compulsion is a response to those obsessive thoughts, a ritualistic behaviour that temporary allays the anxiety but can't rationally prevent the obsession from occurring," study author Dr Emily Miller said.
The most common obsessive thoughts were worries about dirt or germs, followed by compulsions to check that no "mistakes" had been made (many mothers reported checking and rechecking baby monitors are working and sterilising already clean bottles over and over again).
Other women described "intrusive thoughts" that they would unintentionally harm their baby.
"That can be emotionally painful," Dr Miller said. "You don't intend to harm the baby, but you're fearful that you will."
The researchers also noted that around 70 per cent of women who reported OCD symptoms also reported symptoms of post-natal depression.
They said this crossover suggests the existence of a larger postpartum mental illness that needs its own classification and research.
"There is some debate as to whether postpartum depression is simply a major depressive episode that happens after birth or its own disease with its own features," Dr Miller said.
"Our study supports the idea that it may be its own disease with more of the anxiety and obsessive-compulsive symptoms than would be typical for a major depressive episode."
This is the first large-scale study of OCD symptoms in new mothers. A total of 461 women participated in the survey at two weeks and of those, 329 participated in the follow-up six month survey.
The research is published in the April issue of The Journal of Reproductive Medicine.