My Facebook timeline goes through cycles of life milestones –from college graduations to engagements to weddings and now to pregnancy announcements and newborns.

Older Millennials are starting to have families while the tail-end of our generation is just packing up to head to college this fall. We are about to become the biggest generation –beating out our Baby Boomer parents as we grow to 75.3 million next year to compared 74.9 million. And we do things differently from them and the ages at which we’re starting families can be added to that list.

Birth rates for women in their twenties saw a 15-percent decrease from 2007 to 2012, according to a new report by the Urban Institute. This decrease contributed to falling birthrates of women overall after more than 30 years of relative stability.

Big contributors to the steeply declining number of women ages 20-29 aren’t having babies are the Recession of 2007-2009 and the “painfully slow recovery,” according to a new report. While it’s common for the birthrate to decline after a downturn in the economy, it has never been this big a decline.

Also, the recession reduced immigration and recent immigrants tend to have higher birth rates than U.S. natives or less recent immigrants. And birthrates among young Hispanic women fell dramatically – 26 percent. That was followed by a 14 percent decrease among African-American women in that age group and an 11 percent fall for white women.

The report finds:

A dramatic decline in birth rates among unmarried women is the most important factor in the overall reduction in childbearing among African Americans and Hispanics. Among non-Hispanic whites, most of the fertility decline can be attributed to a decline in the share of women married. With the exception of young Hispanics, birth rates for married women did not decline much and even rose for some groups. It remains to be seen whether the Millennial women who eschewed childbearing during the recession years will compensate by exhibiting higher birth rates in their thirties or if this generation will have fewer children than their older counterparts.

There may also be historic changes in the ages for when young women decide to have kids

CNBC reports:

Also, women in their twenties who aren't having kids now could start having kids in their thirties, [Nan Marie Astone, one of the authors of the report], said. That in itself would represent a dramatic demographic change.

Until the 1980s, for as long as records were kept, the highest fertility rates worldwide were among women ages 20 to 24, Astone said.

That shifted in the United States and Europe sometime in the 1980s, when women ages 25 to 29 became the most fertile, she said.

"For demographers, a small group of nerdy people, that was pretty momentous," she said.

"It was associated with women going to school for longer, or going into professional occupations," both of which led women to delay having children, Astone said.

If the birth rates among millennial women rebound by the time they reach their thirties, Astone said, the most fertile age group may become women age 30 to 34 for the first time in human history.

"That would be a big deal," she said.

What’s interesting about these findings are the implications that they have on other sectors, including the public sector.

The authors note that housing and home buying will be affected as homes are generally bought in the expectation of having a family. Perhaps, that explains some of the allure of renting in urban areas among my generation. As we know, the housing industry drives a lot of consumer spending and has rippling impacts across many industries.

Local and state governments as well as the federal Education Department may face noticeable declines in student enrollment until Millennial women start having kids. What happens to the school systems that built new schools and expanded programs to accommodate a big generation? What about the added dollars that go into public education from Head Start programs through high school? And let’s not forget that billions of dollars go to college scholarships, Pell grants and student loans, budgets for public state colleges and universities, and other higher education spending.

In an ideal world, we should see public spending scale back, but that means cutting budgets, layoffs, and reducing the public education behemoth. That’s not a popular sentiment in Washington or across the country, but one that needs to be seriously considered.

If Millennials are just postponing childbearing for few years, then the blow may be muted but if we are opting not to have kids at all, the implications will be serious. Time will tell how this play out.