Women were assessed in the weeks and months after birth
The risk of new mothers developing postnatal depression is cut if health visitors are trained to spot signs and offer psychological help, a study says.
Health visitors were trained to spot symptoms of depression six to eight weeks after birth.
Women who were then given psychological support by health visitors, rather than the usual process of being referred on to a GP, fared better.
Huddersfield and Sheffield University researchers looked at 4,000 women.
At the six or eight-week check, 600 women were found to have signs of postnatal depression.
A third were offered the usual care of a GP referral, while the rest were offered eight sessions of cognitive behavioural therapy, which aims to change behavioural responses, or person-centred therapy where the patient is encouraged to discuss their feelings about their situation.
Both forms of psychological support led to a reduction in depressive symptoms when compared with women in a control group who received the usual level of care.
A third of women who had been given therapy still had symptoms of depression six months after their baby's birth, compared with just under half of those in the control group.
The difference in outcomes remained when women were assessed again at 12 months.
Writing in the BMJ, the researchers led by Dr Jane Morrell, said: "Training health visitors to assess women, identify symptoms of postnatal depression, and deliver psychologically informed sessions was clinically effective at six and 12 months postnatally compared with usual care."
In a second study published in the journal, University of Toronto researchers examined the effectiveness of telephone support to prevent postnatal depression.
Seven hundred women who tests showed were at high risk of developing the condition either received telephone support from volunteer mothers who had experienced postnatal depression themselves, or could seek help from health professionals themselves if they felt it necessary.
Those who were supported were around half as likely to develop postnatal depression 12 weeks after birth.
Around 13% of women are thought to experience postnatal depression following the birth of a child but it is often undiagnosed and untreated.
Antidepressants have been shown to be an effective treatment, but many women are reluctant to take the drugs, especially when they are breastfeeding.
Writing in the BMJ, Dr Cindy-Lee Dennis, who led the study, said their work and that of the UK team provided more evidence that postnatal depression could be effectively treated, and possibly even prevented.
But she said the condition was still undiagnosed and untreated in many women.
"Only by overcoming the barriers to treatment, providing comprehensive screening programmes, and ensuring the delivery of appropriate and timely care will we effectively prevent and treat postnatal depression."