A record number of babies were born in the U.S. in 2007, according to early federal data released Wednesday that some demographers say could signal an impending baby "boomlet."

The 4,315,000 births in 2007, reported as "provisional" data by the National Center for Health Statistics, gives just a glimpse of what's ahead in the nursery.

"I can't tell you anything about who's having these babies, but it is an early look and there is an increase," says federal demographer Stephanie Ventura. "It's a milestone."

She says details about the moms won't be available until the fall, because all the agency has now is birth certificate data from state health departments.

The last time the number was this high was in 1957, in the middle of the baby boom years; some 78 million Americans were born between 1946 and 1964. Demographers have been monitoring gradual increases in recent years; data for 2006, which won't be finalized until September, show a 3 percent increase over 2005. That's the largest single-year increase since 1989.

"I suspect this is the beginning of a new kind of baby boom, although it's going to be nowhere near the baby boom of the 1950s or '60s," says demographer Arthur Nelson of the University of Utah in Salt Lake City. "It will be sort of a boomlet."

To be considered a real boom, demographers say, the percentage increases would have to be much larger than the single-digit increases we're seeing now.

The last time there was talk of a boomlet was during the 1980s and '90s. Those babies were sometimes known as "Echo Boomers" and today are called "Millennials" or "Generation Y."

Nelson attributes the 2007 numbers to a "perfect storm" of factors: more immigrants having children, professional women who delayed childbearing until their 40s, and larger numbers of women in their 20s and 30s in the population, keeping the fertility rate high. The average number of births per woman was 2.1 in 2006, the highest since 1971.

"We have three different phenomena around birth happening at the same time," he says.

But family demographer Ronald Rindfuss, of the University of North Carolina-Chapel Hill, says there is a bigger question looming than who's having kids.

"From the perspective of schools that have to educate these children, this is a real increase in the number of births and something they're going to have to deal with," he says. But it won't be "the kind of shock that we saw at the beginning of the baby boom. In 1952 and '53, in many parts of the country, schools had to run double sessions. This is a gradual increase."