According to a new study published in the journal Human Reproduction, depressed future moms are twice more likely than pregnant women who don’t suffer from depression to deliver preemies.

In the study, researchers followed 791 San Francisco-area women during their pregnancy. The two fifths of participants who were suffering from serious depression symptoms around the 10th week of pregnancy had twice the risk of having a preterm birth.

While heavy with child women with severe depression had twice the risk of giving birth to babies earlier than 37 completed weeks of pregnancy, mild depression triggered an even higher risk - 60 percent.

In view of the study’s results, researchers concluded that there is a strong association between the risk of delivering a baby before 37 weeks gestation and early-pregnancy depression. It is worth mentioning that expectant women in the study hadn’t taken antidepressant drugs, indicating that side effects from the medications couldn’t justify the direct link between the two.

Finding a cause of giving birth to babies earlier than 37 completed weeks of pregnancy, about which a small amount of data is known, makes the findings noteworthy, said study lead author Dr. De-Kun Li, M.D., Ph.D., a perinatal epidemiologist and senior research scientist at Kaiser Permanente's Division of Research in Oakland, Calif.

"Depression during pregnancy really has not been paid attention to," he said. "It has been definitely underdiagnosed, undertreated, and frequently dismissed and ignored."