Call it the Juno effect, the Jolie effect or the Jamie Lynn Spears effect. Whatever you call it, it’s “in” to be a mom. The average number of births per woman reached the magical 2.1 population replacement rate in 2006 for the first time since 1971. The trend has continued. According to newly released U.S. Census Bureau data, more babies were born in 2007 than even during the height of the baby boom — 4.32 million babies in 2007, more than the 4.30 million babies born in 1957.

There’s no question that being pregnant and having a baby looks cooler than ever. First there’s the celebrities reproducing faster than one can read about it in the supermarket tabloids. Then there’s the movies and TV shows. Ellen Page as Juno was spunky, hip and totally emulatable by teens in Gloucester, Massachusetts — and who knows where else? An NBC Reality Show, The Baby Borrowers, is reportedly intended to reveal the sleepless reality of parenthood, but would it be interesting at all if there were no interest in the topic? Knocked Up was a hit romantic comedy.

So who is driving the trend? Is it the Millennial teens and young adults or Gen Xers who delayed having babies to establish careers? The 2007 numbers of births by age of mother are hard to find. However, there are indications that it is the younger women driving the trend. The percent of births to women 15-29 has remained steady at 62 percent from 2001-2005, and there is no reason to believe that proportion has changed in favor of older mothers. Further, according to a report by the Center for Disease Control and Prevention, the birth rate for the youngest teens, ages 10-14, declined; the birth rate for older teens, ages 18 through 19 (73 per 1,000) is more than three times higher than the rate for teens aged 15-17 (22 per 1,000). The biggest jump was among unmarried women aged 25 through 29, among whom there was a 10 percent increase between 2005 and 2006.

The current baby-mania may have its roots in Millennial attitudes. Many no longer feel constrained by a timetable that calls for establishing a career, then a family. Millennials believe they can do what they want, and if a baby is what they want right now, why not go for it? As the products of one of the most successful generations of parents, they have good parenting role models. And as one of the wealthiest cohorts, they may feel they are financial as well as psychologically prepared. Who knows, they may be right? A plethora of babies may be just the latest clue that Millennials are not like Gen Xers.