These seem to be the two main reasons for the decline in the U.S., according to the article.<p>- A public policy demographer says despite more women in their late 30s having children, "it's not making up for fertility declines among younger women. What's coming to appear is that a lot of these babies are just going to be forgone entirely. They're not going to be born."<p>- There's also a decline in teen pregancies, and the article quotes a population center director who attributes that to more effective contraception. "The United States has always had much higher rates of teen and unplanned pregnancies than other countries. This is a success story... that people are able to avoid having births early on, when they themselves would say, 'This is not the right time for me.'"