A study led by Andrew J Cherlin from the Johns Hopkins University in US is the first to trace how the income gap, a large-scale societal trend, affects individual personal choices about starting a family.
The greater the income inequality in an area, the less likely young men and women are to marry before having a first child, according to the study.
"Does income inequality affect a young adult's decision about getting married and starting a family?" asked Cherlin.
"They don't foresee ever having the kinds of well-paying careers that could support a marriage and a family. But they are unwilling to forgo having children," Cherlin said.
"So with good jobs in limited supply and successful marriage looking unlikely, young women and men without college degrees may go ahead and have a child without marrying first," he said.
Researchers found that areas with high levels of income inequality have a shortage of jobs available in the middle of the job market.
Without access to this sort of work, young men can not make an adequate living. They do not see themselves as good marriage material, and their partners agree.
Couples like this might live together and have a child, but they are reluctant to make the long-term commitment to marriage, according to Cherlin.
The team studied 9,000 young people of the generation known as millennials, from 1997 when they were 12 to 16 years old, until 2011, when they were 26 to 31.
Most of the first children born outside of marriage were to women and men who did not graduate from college.
The researchers then matched that information about birth and marriage with census data on income and employment.
They found that childless unmarried men and women who lived in counties with greater household income inequality and fewer middle market jobs available were less likely to marry before having a child.
The research appears in the journal American Sociological Review.
