Today's 20-something women are going child-free, at least for the time being. A new study has found that millennial women have the lowest birthrate of any previous generation in U.S. history — and the economy might be to blame.

According to the think tank Urban Institute, between 2007-2012, birth rates among American women in their 20s declined by 15 percent. In 2012, there were only 948 births per 1,000 women in their 20s, which is the fewest number of births of any generation of young women in this country.

The decline was consistent among all races, but it was most dramatic for Hispanic women, who saw a birth rate decline of 26 percent, followed by black women, at 14 percent, and an 11 percent decrease for white women.

At this point, it's a guessing game as to why women in their 20s are putting off having a baby, but experts say the economy is playing a role. Let's face it, babies are expensive. And today's millennials may still be living with their parents after emerging from college into a tough job market. Past recessions have noted a similar decline in birth rates. "Previous historical low points for 20-something fertility rates occurred in the early 1930s and late 1970s," the Urban Institute paper noted, and both of those eras coincided with an economic downturn.

The birth rate decline could also be attributed to a similar decline in marriage rates among millennials. According to a recent Pew survey, more than a quarter of never-married Americans in their 20s and early 30s have not tied the knot because they say they aren't financially prepared for marriage.

The big question now is whether or not millennial women will "catch up" on the rate of births, as some generations have done after stalling childbearing. If they don't, the lack of births may start to set off alarms. Generational imbalances affect everything from Social Security payouts to seats in a classroom. But for now, experts say, there's no reason to worry.

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