LOS ANGELES, Oct. 25 (Xinhua) -- Women depressed during early pregnancy are more likely to have a pre-term delivery, the leading cause of infant mortality, a new U.S. study has shown.

    Researchers interviewed 791 women around their 10th week of pregnancy in San Francisco city and county and found that 41 percent reported "significant" symptoms of depression, while 22 percent reported "severe" depressive symptoms.

    The women with severe depressive symptoms had almost twice the risk of an early birth, defined as delivery at less than 37 weeks of gestation. Those with significant symptoms had a 60 percent risk of an early birth, according to the study conducted by scientists at Kaiser Permanente's research division in Oakland, California.

    Discovering a possible cause of pre-term delivery, about which little is known, makes the findings significant, said the study's lead author Dr. De-Kun Li, a perinatal epidemiologist and senior research scientist at the division.

    Scientists have been studying the causes of high rates of infant mortality in the United States, Li said, but, "we don't know what is going on. If we can find something as obvious as depression that can be treated during pregnancy, that is very, very significant."

    The findings have been published in the October issue of Human Reproduction, an Oxford University Press journal.

    Li hopes the study's findings will make "antenatal depression" as widely recognized as postpartum depression has been. Until now, depression during pregnancy has been "under-estimated and under-treated," he said, "not just by women, but also by their doctors."

    One reason for this lack of attention is that there is no strong evidence of a connection between the depression of pregnant women and harm to the foetus, Li said.

    The study also found that women who are more likely to report depressive symptoms tend to be younger than 25, unmarried, less educated, poorer, black, and have a history of pre-term delivery.