Along with the recession, the drop may have something to do also with recognition, as the teen rate rose in 2006 and 2007, of problems with Ab-only ed — and moves in a number of states away from that.
Likewise, all the additional people who had babies in 2007 (that rise occurred in all age brackets except those 45+ and those 14 and under) were busy in 2008 — taking care of those kids. Demand in the baby realm is not infinite.
On the other hand, recession-based decisions against a baby today among folks who would have otherwise felt ready, will lead to further increases in births to older moms (and dads) down the line. Lots of ripple effects to all these social dynamics.