Research evidence shows that symptoms of postpartum depression decrease over time -- but depression remains a long-term problem for 30 to 50 percent of affected women, according to a report in the January Harvard Review of Psychiatry. The journal is published by Lippincott Williams & Wilkins, a part of Wolters Kluwer Health.

"Families with mothers suffering from postpartum depression need the engagement of clinicians who are sensitive to the signs of the depression potentially becoming chronic," according to the research review by Nicole Vliegen, Sara Casalin, and Patrick Luyten at the University of Leuven, Belgium. Because parental depression can adversely affect children's long-term development, the findings also highlight the need for ongoing support during early childhood and beyond.

Differing Reports on the Course of Postpartum Depression

Dr Vliegen and coauthors performed a critical review of the research on postpartum depression from 1985 to 2012. They focused on the course of postpartum depression during follow-up -- including factors that may contribute to a higher risk of developing chronic depression.

In all follow-up studies of women with postnatal depression, scores for depressive symptoms decreased over time. However, the scores did not always fall below clinical cutoff points for depression. In community-based studies, 30 percent of mothers diagnosed with postpartum depression were still depressed up to three years after delivery.

In clinical samples -- that is, patients receiving medical care -- about 50 percent of women remained depressed throughout and beyond the first postnatal year. For all studies combined, the median rate of persistent depression was 38 percent.

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Several studies sought to identify subgroups of patients with different outcomes; all reported a subgroup of women with persistent depression. Most studies also identified a subgroup of women who had acute major depression during the first three months, but who no longer had elevated symptoms at six months or beyond.

Some Factors Linked to Higher Risk of Chronic Depression

Other studies found a "decreasing depression" subgroup, whose symptoms improved but never resolved completely. Some reports suggested that chronic postpartum depression may represent a continuation of pre-existing depression or other mood symptoms.

Some research suggested that younger mothers, those with lower income, and minority women were at higher risk of chronic postpartum depression. There was more consistent evidence for other "contextual" risk factors, including lower quality of the partner relationship, a history of depression or sexual abuse in the mother, higher parental stress, and personality factors. Colic or other illnesses in the infant did not seem to affect the risk of chronic depression.

Previous studies have reported that maternal depression can adversely affect child development, including cognitive and verbal abilities and school readiness. "Because PPD has significant consequences for the baby, for the depressed mother, and for the early relationship between mother and child, knowledge about prolonged changes in the mental health of mothers with PPD may not only improve our understanding of the course of PPD, but also inform prevention and intervention strategies," the researchers write.

Dr Vliegen and colleagues note some important gaps in the research -- including a lack of data on how treatment for postpartum depression affects long-term outcomes. They make recommendations for further research, including larger studies using a standard definition of postpartum depression and consistent follow-up.

Meanwhile, the authors believe their findings have important implications for healthcare providers caring for women affected by postpartum depression. They write, "Clinicians need to be aware of mothers' previous episodes of depression and possible contextual factors heightening vulnerability for a chronic course of depression."