"We found that mothers who were highly depressed didn't invest emotionally or in providing learning materials to support their child, such as toys and books, as much as mothers who were not depressed. This, in turn, impacted the child's IQ at ages 1, 5, 10 and 16," Patricia East, PhD, research scientist with the Department of Pediatrics at UC San Diego School of Medicine and one of the lead authors on the study said in a statement.
"The consistency and longevity of these results speak to the enduring effect that depression has on a mother's parenting and her child's development," she added.
Researchers found that signs of depression in mom when the child is 1 is associated with lower scores on cognitive function tests for the child at age 16.
The authors found the relationship in reverse to be true, as well -- lower development scores early in the child’s life promoted less engagement from mom and that only increased signs of maternal depression as the child entered into adolescence.
This connected relationship between early maternal depression and early development delay in children appeared to increase the problems further by damaging the mother-child support relationship.
The study data suggests approximately 20 percent of mothers who are severely depressed when their children turns age 1 remain depressed for a long time, East said.
Pediatricians need to be on the alert to both developmental delays in children and maternal depression, the study authors noted, because the broader research has shown how prevalent maternal depression can be and how much it can affect the children.
"Although seemingly small, differences in IQ from 7.78 to 7.30 are highly meaningful in terms of children's verbal skills and vocabulary," says East. "Our study results show the long term consequences that a child can experience due to chronic maternal depression."
However, the authors recognize these families in Chile “may not be representative of mothers or children of other cultural backgrounds or nationalities.”
All the families studied were from a similar cultural background, socioeconomic status and had a similar level of education, which an be a limitation, but the authors argue also helped control for outside factors influencing the results of the study.
This study also observed, but did not test the impact of fathers or the presence of other siblings, and those may also have a large impact on both maternal depression and childhood development.
These findings reinforce already established theories in the child development literature, but the unique feature of this study is tracking the effects from infancy through adolescence.
The authors also called for enrichment programs to help children with early delay reach their full potential.
David J. Kim, MD is a final year Emergency Medicine resident at the University of California, Los Angeles, working with the ABC News Medical Unit in New York.