One in four pregnant women suffers from mental health problems and scientists say identifying issues early could be vital for a healthy pregnancy.
Although in line with the national average, research by scientists at King's College London further debunked the myth that pregnancy boosts physical and mental health.
Nationally an average of one in five women experience some form of mental health disorder during their lifetimes, while this jumps to one in four in young women.
Depression and anxiety were among the most common disorders among pregnant women but eating disorders and obsessive compulsive disorders both made up two per cent of cases.
The study, the first of its kind in the UK, aimed to identify how common disorders were during pregnancy and how midwives can best identify them to ensure a speedy referral to mental health services.
One of the study's authors, Louise Howard, professor of women's mental health at King's College, said they wanted to establish the prevalence of the range of disorders because there has been a tendency to focus on depression in the past.
"As mental disorders in general can affect women and their families, it was important to know just how common all the disorders were," prof Howard said.
"Our findings support the idea that pregnancy is not protective, which is what people used to think.
"There was a myth that pregnancy was a time of great blooming health and it was the postnatal period that was the one to be concerned about when people were thinking about mental disorders."
She emphasised that pregnancy was not necessarily a cause of a mental health problem but said it could provide medical professionals with a great opportunity to identify an issue.
It has been proven that mental illness during pregnancy is associated with adverse outcomes for women, the pregnancy itself and the child, so early identification could be key to mitigating the worst effects.
The research was funded by the National Institute of Health Research and focused on a sample of 545 pregnant women over the age of 16 attending a south-east London maternity clinic.
Australian readers seeking support and information about depression can contact Lifeline on 13 11 14.