Depression and Speech Delays

An article from CNN talks about research that is being done on whether the mom's depression could have an affect on a child's speech development: 

The babies in the control group, whose mothers did not have depression, performed as expected: They tended to succeed in language discrimination tasks at 6 months old and failed at 10 months old.

But the infants whose mothers had depression (but were not taking antidepressants) failed at 6 months and succeeded at 10 months. That means their critical period for language sensitivity was delayed.

Read the complete article: http://thechart.blogs.cnn.com/2012/10/08/does-moms-depression-affect-babys-language/?hpt=hp_bn12

I have two children with speech delays, and didn't have depression during either of their first years.  I find these studies interesting, but they also tend to put a lot of guilt on the moms to feel that they are to blame.  How do you feel about this article?