I think it's dangerous to extrapolate from one incident and see this as a harbinger of "real culture change." I looked up teen pregnancy rates in the US, and it seems that they've been declining sharply: "Teenage birth rates fell one-third from the 1991 peak (61.8 per 1,000) through 2004 (41.1) (Table 2 [on p. 3]), and continued to decline through 2005 (by 35 percent to 40.5) (11)."

So I agree that all we really see is that "a fad for childbirth seems to have seized a number of teen-age girls in one place in the USA."