Constance Hammen, Ph.D., and Patricia A. Brennan, Ph.D., investigated the relationships among the timing, severity and duration of a mother's depression and depression in children with use of data on 816 women and their 15-year-old children in an Australian community. Measurements of maternal depression severity and duration and dates of occurrence allowed the researchers to analyze how the relative severity, timing, and duration of maternal depression affected development of depressive and nondepressive disorders by the teenage years in their children.

The researchers found that children who were diagnosed with depression at age 15 years or less were twice as likely (20 percent versus 10 percent) to have mothers who were depressed. Nondepressive disorders in youth were also more common among children of depressed women (22 percent versus 15 percent), with anxiety disorders especially closely associated with maternal depression.

After controlling for demographic factors, severity of maternal depression contributed more to children's risk for depression than did the timing of the depression. Children exposed to 1 to 2 months of maternal depression or to more than 12 months of mild maternal depression had elevated risk for depression. Timing of exposure to maternal depression did not predict children’s risk.

"Overall, the study gives a more precise answer to the question of children's risk for disorders due to maternal depression. It underscores concern about the deleterious effects of significant maternal depression---whether even brief major depressions or subsyndromal but enduring depression---and the need to increase our efforts to reach parents who are reluctant to seek treatment," wrote the authors.

They added, "At the same time, it may reassure those who have been worried that mild but brief periods of depression are harmful. The findings encourage further efforts to shed light on the risk of mechanisms and processes by which parental depression affects children."