A new study shows that teenagers whose mothers were depressed during pregnancy are more likely to have psychiatric issues.

Researchers from the University of Bristol in the United Kingdom also found that post-partum depression was linked to children's mental state later in life, but perhaps for different reasons. Mothers who experience depression after giving birth has an effect on the child as well, Rebecca Pearson, one of the authors of the study, told Reuters. Stress hormones that cross through the placenta cause this passing-on of mental issues.

These findings stand in contrast to a hypothesis posited by some researchers who claim that depression is only significant if it continues past birth, changing the way a family raises a child.

"It should be treated during pregnancy, irrespective of if it continues during birth. It's as important during pregnancy," Pearson told Reuters, adding that it is important that mothers have therapy services available to them while they are carrying children.

These findings also add another issue to the mound of debates over the use of antidepressants during pregnancy, Reuters reported.

The researchers assembled data from an extensive study that started following English pregnant women who were due in 1991 and 1992 - the mothers were interviewed twice while pregnant and twice during their baby's first year concerning their state of mind. Around 12 percent of the women were labeled as depressed during pregnancy, while seven percent remained depressed after they'd given birth to their children.

Over the next 16 and 17 years, researchers administered surveys to the families. When the children had turned 18, about eight percent of the 4,500 kids surveyed gave reports that they'd experienced symptoms of depression. Teenagers were 47 percent more likely to be depressed if their mothers were depressed while pregnant, Reuters reported. Even after they'd given birth, the results were unchanged.

Still, the study doesn't ensure that teens will be depressed in later life if they've been exposed to depression while their mothers were pregnant.

Teens were more depressed more often if their mothers' depression continued the year after they were born. But when the writers of the study took a look at other factors of familial life, they realized that depression only lingered in families at an economic and educational disadvantage.

"Postpartum depression seems to have a negative impact on children's development because it affects how responsive mothers are to their babies," Laura Scaramella, who has studied maternal depression, but was not involved in this study, said. "It inhibits their ability to really attend to and respond to their baby."

The study was published in JAMA Psychiatry.