ADHD is now one of the most common pediatric neurodevelopmental disorders, affecting up to 7.2 percent of all children.
The condition raises the likelihood that the child will face difficulty at school and later in life. Also, some evidence suggests that ADHD increases mortality rates.
And worryingly, according to some reports, the incidence rate of ADHD is steadily rising. Although better detection rates certainly play a part in the increase, this cannot explain the size of growth.
Therefore, the race is on to understand what causes ADHD and, importantly, whether or not it can be prevented.
Maternal depression and ADHD
A group of researchers recently investigated the role of depression during pregnancy in ADHD risk. Although scientists have explored a range of potential causes of ADHD, maternal depression has received relatively little attention.
The sparse literature on this interaction has been inconclusive. However, the authors of the current study believe that this lack of clarity might be due to methodological flaws.
Such flaws include the fact that earlier studies only quantified depression at one or two points in time during pregnancy, rather than throughout. Also, the effects of depression after pregnancy were not taken into account.
Another potential issue in previous work is explained by the authors. "The studies failed to account for maternal pre-pregnancy obesity and common pregnancy disorders," they explain, "which in addition to increasing the child's ADHD risk, may often also accompany maternal depression."
The team designed a study to reopen the question and address the issues outlined above. So, in this experiment, depressive symptoms were measured biweekly from 12 weeks pregnant until delivery.
Children were followed until the age of 3–6. At this point, the scientists registered details about the mother's depressive symptoms following pregnancy. Data regarding pre-pregnancy obesity, hypertension disorders during pregnancy, and gestational diabetes were also collated.
Study sheds light on depression-ADHD link
In all, 1,779 Finnish mothers and their one child, born 2006–2010, were included in the study. Their assessment began at the 12th week of gestation, and the final assessment took place when the child was an average of 3.8 years old. The researchers' findings were recently published in the journal PLOS One.
Following analysis, the authors found that the proportion of "children with clinically significant ADHD symptoms were higher in the group of women who had consistently high depressive symptoms throughout pregnancy."
In short, ADHD was more commonly found in the offspring of depressed mothers, and their symptoms were significantly worse.
If the mother experienced depressive symptoms after birth, this added to the effects of depressive symptoms during pregnancy: there was a further increased risk of ADHD and more pronounced symptoms.
Contrary to expectations, maternal obesity and pregnancy disorders — such as maternal diabetes — did not influence ADHD outcomes in the offspring. Similarly, when depressive symptoms were split into trimesters, there were no time-specific effects. This was because, in general, those mothers who were depressed during pregnancy were depressed throughout.
What might cause this interaction?
The study's findings are clear cut, but as the authors write, "An obvious study limitation is that we are not able to specify the brain structural or functional nor biological or behavioral underlying mechanisms."
This will be the next step, and a number of potential mechanisms have already been proposed. For example, earlier studies showed that maternal depressive symptoms, salivary cortisol levels, or both might alter a baby's brain structure and the way that it is connected.
Depression during pregnancy has also been linked with an increase in placental glucocorticoid sensitivity, which could have a wide array of effects on fetal development.
It will take time to unravel how and why maternal depression is linked to ADHD, and it is likely to be a complex picture involving all of the processes above and more. However, for now, the current findings can still be clinically useful.
As the authors write in their conclusion, "[P]reventive interventions focusing on maternal depressive symptoms may benefit not only maternal but offspring well-being."