Women might not see equal pay for decades. (iStock)

After graduating from college, men and women earn almost the same amount -- and in some fields, even more -- during their first years in the workforce, according to new research from the Federal Reserve Bank of New York.

Too bad it doesn’t last.

Economists Jaison A. Abel and Richard Deitz found that women who have recently graduated from college make about 97 cents for every dollar their male counterparts take home -- a much narrower gap than the national average of 82 cents. In fact, for 29 of the 73 majors they analyzed, women actually outearned men. The traditional gender pay disparity was reversed in fields ranging from philosophy to aerospace engineering to social services.

But victory -- if you can call it that -- is fleeting. By the time men and women reach the middle of their careers, between the ages of 35 and 45, the gender pay gap is back and bigger than before. Mid-career college-educated women make just 85 cents for every dollar paid to their male coworkers. Even worse, those fields in which women outearned men? The tables have turned.

Women who majored in construction services, for example, enjoyed an 8 percent premium over men when they were fresh out of college. But within a few years, men’s wages outpace women’s by 24 percent.

So once again, women are stuck taking two steps forward and one step back. The reasons why are outside the scope of the research, though the authors suggest several theories.

If the gender pay disparity is an example of discrimination against female workers, perhaps it manifests more strongly later in a career. The pay gap could also be more about motherhood than gender. In the first years after graduating from college, most workers -- male or female -- are single and childless. But by mid-career, many of them have started families. And since most of the burden of childcare -- and all of the burden of childbirth -- falls on women, several studies have shown that working mothers’ wages and career prospects take a hit as a result.

"It’s not clear what’s driving these differences," Deitz said. "It’s something we wanted to start a conversation about.”