More than 1 in 10 women of child-bearing age have had major depressive symptoms in the previous year, representing about 1.2 million U.S. women, but more than half were not diagnosed and about the same percentage received no treatment, new research shows.

Major depression affects up to 16 percent of U.S. women, aged 18-44 years, and pregnant women have a higher rate of undiagnosed symptoms than those who are not expecting, according the study, published in Journal of Women's Health.

For the study, researchers from the Centers for Disease Control and Prevention tracked depression diagnoses and treatment among pregnant and non-pregnant from 2005 to 2009.

In addition to finding pregnant women were less likely to diagnosed and treated for depression, researchers found disparities based on age, race, ethnicity and insurancde status.

"As health care providers, we simply must do a better job at diagnosing depression and referring women for mental health treatment," said Dr. Susan G. Kornstein, the journal's editor in chief, in an editorial accompanying the study. 'Reproductive health care visits provide an opportune time to address this."