Economic pressures that trigger 20-somethings to delay marriage are harming Americans without college degrees, a new report finds.

In contrast, the marriage delay seems to benefit the college-educated, who tend to wait to have kids until after they've married. For those not college-educated, age at first childbirth is now lower than age at first marriage, a situation that can lead to family instability and increased economic struggles.

"Their kids are much more likely to experience family instability and single parenthood, which are linked to a number of economic, social and emotional problems for adults and for children," said W. Bradford Wilcox, one of the report's authors and the director of the National Marriage Project at the University of Virginia.

But solving the problem likely isn't as easy as exhorting young people to get to the altar. Real economic pressures are helping drive the marriage delay.

Marriage by the numbers

The new report, available online, is a joint effort of the National Marriage Project, the National Campaign to Prevent Teen and Unplanned Pregnancy and the Relate Institute. The Relate Institute is a nonprofit institute established by marriage researchers at Brigham Young University whose members create questionnaires designed to strengthen and assess premarital and marital relationships.

The report pulls together data from a number of long-term national studies on marriage and relationships. The results hold when taking into account demographic characteristics, such as race, ethnicity, education and family background; however, they are correlational. That means that marriage is linked to well-being, income and other measures of success, but it's not clear whether marriage itself boosts these outcomes. It's possible that some of the difference stems from the types of people who choose marriage versus the types of people who don't — the marriage-minded may be more well adjusted in general.

Either way, young Americans are increasingly delaying marriage. The median age of first marriage is now about 27 for women and 29 for men, up from about 21 for women and 24 for men in 1950, according to the U.S. Census Bureau. [See State List of Marriage Ages: from Alabama to Wyoming]

Story continues

Age at first childbirth originally tracked with marriage trends, the report's authors found, increasing as age of first marriage did. But that trend has not held. Around 1990, the median age of first birth in America "crossed over" with the median age of first marriage, meaning children are increasingly coming before weddings.

Today, 48 percent of all first births are to unmarried women. But not all unmarried women are equal. There is no crossover of birth and marriage among college-educated women; they're still marrying, on average, before having kids. Among women with high-school educations or only some college, however, 58 percent have their first child before their first marriage.

Why wait?

Economics is a major driver of these trends, the report's authors found. In the last 40 years, job opportunities for the high-school-educated have collapsed; increasingly, entry-level jobs require a college degree.

At the same time, both men and women feel the need for economic independence before marriage, so that they'll have an economic safety net in the event of divorce. [6 Scientific Tips for a Successful Marriage]

"Under these circumstances, it is no surprise that growing numbers of Middle Americans are postponing marriage to their late twenties or thirties, or foregoing marriage altogether, as they search for jobs that will provide them with a middle-class lifestyle," the authors write.

In many ways, delaying marriage does bolster economic power and earnings potential — but unequally. On average, a female college graduate married before age 20 earns $32,263 annually. If she waits until after 30 to marry, she can expect to earn an average of $50,415 a year.

In comparison, women without college degrees get only a minuscule boost. A woman with a high-school diploma or some college who marries before age 20 earns an average of $18,234 a year. If she marries after age 30, she can expect an average of $22,286 a year.

As non-college-educated men and women wait to marry, however, they still form relationships and families. The difference is, they substitute cohabitation for legal union. Half of 22- to 24-year-old women without a high-school degree live with a boyfriend, for example, as do 30 percent of those with a high-school diploma or some college.

With little hope of career advancement or fulfillment without a college degree, many women in this situation may turn to motherhood for meaning and satisfaction, the report found. In one survey, a third of women and men who said it was important to avoid pregnancy also said they'd be at least somewhat happy to have a child. Unintended pregnancies are also common in 20-somethings, with half of births in this age group unplanned.

Should marriage be fixed?

The trend of putting baby before marriage is troubling, Wilcox and his colleagues say, because cohabitations are more likely than marriages to break up. About 39 percent of 20- to 29-year-old women who are cohabiting when their first child is born will break up before that child reaches age 5, compared with only 13 percent for married women. Such family instability puts children at higher risk of psychological and academic problems. (Marriage is also linked to happiness for couples.)

Less-educated Americans are more likely to divorce than their more-educated counterparts, so it's true that some cohabitating couples would have split even with rings on their fingers, Wilcox said. But the numbers reveal that at every level of socioeconomic status, cohabiting is less stable than marriage.

"People who are getting married are more likely to go the distance than those who are just living together," he said.

What to do about the marriage and childbearing crossover is less clear. The researchers aren't suggesting that young people go out and get hitched at 24, regardless of circumstance. In fact, young Americans are taking marriage more seriously and deliberately than generations past, Wilcox said, which is in many ways a good thing.

"But they're not approaching parenthood with the same degree of deliberation," he said. "We think that young adults should be as deliberative about becoming parents as they are about becoming married. On average, it's best to sequence marriage first, parenthood second."

A cultural shift that sees mid-20s marriage as something to be encouraged rather than questioned could help encourage this change, the report's authors wrote. And national and state-level policies could even the marriage playing field for the non-college-educated, Wilcox said.

For example, the federal government could expand the child tax credit and extend it to payroll as well as income taxes, as payroll taxes are a larger chunk of low-income Americans' tax burden. That would put real money in the pockets of struggling families. Family-friendly work policies could help integrate family life into the 20s, preventing young adults from having to get all their financial "ducks in a row" before thinking of embarking on marriage and family. Vocational training programs could help those who don't want or can't afford a college degree find employment capable of providing for a family, Wilcox said.

"I think part of the story here is economic," he said. "We think it's important to renew the economic foundations of family life in Middle American and poor communities."

The Brookings Institution will hold a town hall on the report's findings at 9:30 a.m. EDT Wednesday (March 20) to discuss policy implications of the report.

Follow Stephanie Pappas @sipappas. Follow LiveScience on Twitter @livescience, Facebook or Google+. Original article on LiveScience.com.

Copyright 2013 LiveScience, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.