One in three first-time mothers suffers symptoms of depression linked to their baby's birth while pregnant and/or during the first four years of the child's life, according to research.

And more women are depressed when their child turns four than at any time before that, according to the study, which challenges the notion that mothers' birth-related mental struggles usually happen at or after the baby's arrival.

The findings have led to calls for all women giving birth in the UK to have their mental health monitored until their child turns five to ensure that more of those experiencing difficulties are identified.

The results are based on research in Australia, but experts believe that about the same number of women in the UK experience bouts of mental ill-health associated with becoming a mother.

In all 1,507 women from six hospitals in Melbourne, Australia, told researchers from the Murdoch children's research institute and royal children's hospital in Parkville, Victoria, about their experience of episodes of poor mental health at regular intervals until their child turned four.

The authors found that almost one in three first-time mothers reported "depressive symptoms on at least one occasion from early pregnancy to four years postpartum [and that] the prevalence of depressive symptoms was highest at four years postpartum". The women's depressive symptoms are often short-lived episodes and do not mean that the women were diagnosed with postnatal depression. Studies in both the UK and internationally have estimated that between 10% and 15% of new mothers suffer from that clinical condition.

The researchers also found that four years after the child's birth 14.5% display depressive symptoms, of whom 40% had not previously reported feeling very low. At that time, women with only one child were much more likely (22.9%) than those with two or more offspring (11.3%) to be depressed.

Dr Jim Bolton, a member of the Royal College of Psychiatrists and a consultant psychiatrist at a London hospital, said that one in three women giving birth in the UK were likely to become depressed at some point during those first four years. "If a similar study was done here, I wouldn't be surprised if the results were similar. Usually the sorts of mothers who are at greater risk of depression are younger mothers who feel they can't cope and mothers living in situations of adversity or deprivation or partner violence," he said.

"These findings are about depressive symptoms, which can be very short-lived, not a formal diagnosis of illness or postnatal depression. This study isn't saying that one in three women gets that," stressed Bolton, who treats mental health problems in pregnancy and after birth among new mothers in his hospital's women's health unit.

The authors recommend that the UK overhauls its monitoring of maternal mental health, which focuses on pregnancy and the early years after birth, because more than half the women who experience depression after becoming a parent are not identified by GPs, midwives or health visitors.

More women could have postnatal depression than the usual estimate of 10%-15% partly because women may mistake the signs of it – which include being more irritable than usual or unusually tearful, inability to enjoy being a parent or worrying unduly about the baby's health – as being things undergone by all new mothers.

Health professionals do not always spot it or ask the right questions to identify it, though are far more aware of it than ever, Bolton added.

One leading psychiatrist said that the one in three women who had depressive symptoms was between two and five times higher than the estimated number of people in the general population who would experience serious low mood in their lifetime, but was higher than the number of women who experienced the most severe forms of depression. Between 5%-10% of people generally suffer major/serious depression during their lifetime.The study, published in BJOG: An international journal of obstetrics and gynaecology, is the first to follow a sizeable number of new mothers for as long as four years after birth. Elizabeth Duff, senior policy adviser at the parenting charity the NCT, said: "This study has included mothers for four years after birth, so suggests that perinatal mental health needs to be monitored for a longer period. Given the devastating effects of postnatal depression, health professionals should give equal consideration to the mental and physical health of parents with young children."

A Department of Health spokeswoman said it welcomed any new research that would lead to women receiving better help with maternal depression.

"We want to do everything we can to make sure women and families get as much support as possible throughout pregnancy and beyond. That's why, earlier this month, we announced that expert training in mental health will be rolled out for doctors and midwives to identify and help women who are at risk of depression or other mental health issues," she said.

Numbers of midwives and health visitors have been growing under the coalition, while specialist mental health doctors and midwives will help improve earlier diagnosis of such problems, she added. However, the Royal College of Midwives said that even more midwives were needed to ensure mothers received the best possible care of their psychological welfare.