A new report from the Urban Institute finds millennial women are having fewer babies than previous generations.

A new study shows that millennial women are having fewer babies. (Wavebreakmedia Ltd, ThinkStock)

No one is exactly sure why this is happening, or how it may play out in the future.

Between 2007 and 2012 the birth rate among women fell 15 percent," said Nan Astone, a senior fellow at the Urban Institute and one of the authors of the report.

Astone said women typically have fewer babies when they're not married

"So for non-Hispanic white women that seemed to be the main thing that was going on," she said. "They just didn't get married as much as Generation X did and the generations before them."

Astone also said that in the past, most recessions have been accompanied by phenomena like this, although this is much more extreme than what we've seen before.

"Usually when there's a recession, the fertility of women in their 20s is lowered a little bit, but typically a few years after that what you notice is birth rates among women in their early 30s go up. They kind of compensate for it. We're not sure if that will happen or not," Astone said.

Dr. Deborah Carr, a sociology professor at Rutgers University said the pattern presents several implications but they're not necessarily bad.

"One reason why this may be happening is because more younger women in their 20s are still in school. They want to be established in their careers before they go about having children, and that actually bodes well for mother and child," she said.

Carr also said "having parents that are slightly older and more established is linked with all kinds of positive child outcomes, everything to their health to their mental health, their performance in school, as well as low rates of crime and criminality."

However, if a growing number of women are deciding to not have kids at all, she stressed that could have major negative ramifications.

"It would mean that we wouldn't have enough workers to fill our workforce, we wouldn't have consumers to generate profits for major corporations and perhaps most importantly at the personal level those who don't have children or have very few children may not have somebody to care for them in old age," she said.

According to Carr, it's still too soon to tell whether the pattern will continue, or if millennials will begin having kids when they're in their 30s.