The findings show the need for doctors to closely monitor women with postpartum depression, said the researchers, from the University of Leuven, in Belgium. Parental depression can harm a child's long-term development, they said.
The study also underscores the importance of ongoing support during early childhood and beyond, the researchers said.
"Clinicians need to be aware of mothers' previous episodes of
depression and possible contextual factors heightening vulnerability for a
chronic course of depression," the researchers said in a news release from
the Harvard Review of Psychiatry.
For the report, the authors examined studies on postpartum depression conducted between 1985 and 2012. The analysis revealed that 30% to 50% of women with postpartum depression developed long-term depression.
Some of the studies suggested that younger mothers, those with lower incomes and minority women were at increased risk of long-term depression. But the review authors said there was more consistent evidence for other risk factors, including a poor relationship with a partner, a history of depression or sexual abuse in the mother, high levels of parental stress, and certain personality traits.
Colic or other illnesses in the infant did not appear to affect the risk of chronic depression, the researchers said.
Can harm children's development
They also said postpartum depression can harm a child's development and the early relationship between mother and child.
"Knowledge about prolonged changes in the mental health of mothers with [postpartum depression] may not only improve our understanding of the course of [the disorder], but also inform prevention and intervention strategies," the researchers said in the news release.