In the weeks and months after childbirth, between 10 and 20 percent of all women suffer from postpartum depression, a mood disorder characterized by sadness, irritability, anxiety and exhaustion.

New research from the University of Rochester Medical Center finds that some women can develop new symptoms later in the postpartum year and sustain them over many months.

Linda Chaudron, assistant professor of psychiatry and lead author of the study, says approximately one-third of the women continued to have high level of postpartum symptoms across the postpartum year. More than a quarter, 26 percent, developed new symptoms. In other words, "they were not considered to have depression in the first three months post partum, but became depressed later on in the year."

Chaudron says the findings suggest that women develop symptoms at different times during the postpartum year and that more frequent screenings could better identify mothers at risk. She says recommended well-child visits could be a perfect venue for such tests. "There are well-child visits at 2 weeks, 2 months, 6 months, 9 months and 12 months post partum. And, all of those are opportunities to ask moms how they are doing and potentially screen them and intervene if they need help at that time point."

Chaudron says future studies on the natural course of postpartum depression must target some important questions: "Are the women who may become depressed in those first three months different in some way -- different than the women who become depressed later on in the post-partum year, and therefore do we need to identify women differently? Do we need to intervene differently? Can we help prevent it for some women who may become depressed later on rather than early on?"

The research on post-partum depression is published in the July/August issue of the journal Ambulatory Pediatrics.