Just a clarification to my comment.

If I remember correctly, I don't think the claim was teen pregnancy was the "primary driver of population growth" but one of the variables that has a large impact on fertility rates. Most people see the reduction in teen moms as a positive development.

I also think the reduction in unplanned pregnancy to be a net positive. So 20 somethings finishing school before starting a family is good, but it's also probably resposible for fewer large families. I believe polling shows most woman want more children than they actually end up having. I'm sure part of that explanation is that people are starting families later in life.