I did my dissertation at uni on teenage pregnancy, I compared health stuff, income and loads of other measures of deprivation. And basically, my conclusion was this:
If the place is a shithole, there will be more pregnant teenagers.
My personal opinion is that GENERALLY, the better off you are, the more intelligent you are, therefore you have more in your life to look forward to than just having a baby. Many of these young girls feel like they have nothing to look forward to except leaving school and getting a shit job... so having a baby is the next logical step.
I think it's extremely sad.
I concur with your thoughts. If you have a shit/lonely life then you are more likely to want to bring someone else into the World almost as a fix to your own problems.