By Tiziana Barghini

(Reuters) - Susanna Mancini cherishes a photo of herself at 27: a smiling face behind a pair of dark sunglasses. On it, she scrawled to her future husband: "Too bad you can't see my eyes. I am so proud of my tough yuppie stare!"

Her professional pride propelled her early career as a lawyer. She was successful and well paid for it. She kept working when her first child was born and was promoted to a more senior position in Citibank after her second child arrived.

But her career eventually succumbed to something Mancini never expected would end her rise at the bank - her husband's even bigger success. She quit in 2005 when her six-digit income was overtaken by his seven-digit one.

"At that point, it was clear that my wage had become family pocket money. There was a real opportunity to do other things that did not require being chained to a desk," said Mancini, now 50.

She is far from alone, according to a new study from the Federal Reserve, due to be published shortly.

It shows that between 1993 and 2006, there was a decline in the workforce of 0.1 percent a year on average in the number of college-educated women, with similarly educated spouses.

That contrasts with growth of 2.4 percent a year between 1976 and 1992.

The result: the labor force in 2008 had 1.64 million fewer such women than if the growth rate had kept up its earlier trend, slightly more than 1 percent of the total workforce in that year.

SKILLED EXODUS MAY HURT GROWTH

Stefania Albanesi, a senior economist at the Federal Reserve Bank of New York and one of the study's authors, said the loss may hurt economic growth at a time when the nation can ill afford to have highly skilled workers on the sidelines.

While the overall jobless rate remains high, the United States faces skill shortages in some areas and the unemployment rate for college graduates is just above 4 percent.

Albanesi links the decline in the number of well-educated, married women entering the labor force to a sharp rise in salaries for top earners in the United States, and in particular, for men.

In 1975, college graduates of both sexes were making 43 percent more than non-college graduates. By 2008, the figure had risen to 92 percent for men and to 70 percent for women.

"In the last 20 years, wages for highly educated males increased so much that they dwarfed the family's second income, usually the one of their wives," said Albanesi, who co-authored the study with Columbia University graduate student Maria Prados.

"The result was that sometimes married women exited the labor force mid-career, exactly around the time their husbands are promoted to more senior roles. They stopped getting income they didn't need and so they left the labor force forever."

In a previous study, Albanesi estimated that the rise of all women participating in the labor market boosted gross domestic product by 42% percent between 1920 and 1990.

Once the 2007-2009 recession hit, the female retreat from the workforce halted for a couple of years: Women and men alike returned to the workforce when their spouses lost jobs or when their incomes fell, and also to make up for a loss in the value of housing and stocks.

But as the economy stabilized in the past two years, there have been signs that the retreat has resumed, Albanesi said. Of all working-age women, 58.6 percent were either working or looking for a job in 2010, down from 59.2 percent in 2009. The Bureau of Labor Statistics expected the rate to fall further by 2020.

According to Albanesi, it's not the tug of looking after young children that makes most educated women give up their career.

"These women usually give up their jobs when their children are school-age and not babies any more," Albanesi said.

Studies by the University of Chicago Booth School of Business and Harvard support that view.

Albanesi plans further research to quantify how much the decline in educated women in the workforce is affecting the potential growth rate of the economy.

NOT JUST FOR A FEW

Only a few households can afford to give up a good second income.

But the trend is not limited to top earners. It has been detected among households earning around $80,000 per year.

Julie Divita worked 18 months as an entry-level marketing assistant for a company that makes Hawaiian shirts before leaving to have a child.

"I was planning to go back to work, but ironically, on the first day of my maternity leave, my husband got a raise that was the equivalent to my salary. This was 25 years ago, and I have been a 'stay at home' ever since," Divita said.

She is married to a partner in a property development firm in the San Francisco Bay Area and spends much of her time fund-raising for local schools as a volunteer.

Some of the rarer stay-at-home husbands have similar stories.

"He was laid off three years ago. He has been looking for a job, but he's probably not been so motivated about seeking one," said a woman with a senior position on Wall Street, who spoke on condition of anonymity.

She said the quality of life for her family, including their daughters, ages 14 and 12, has greatly improved, though explaining why the male is not the breadwinner can still be socially awkward.

"Stay-at-home wives are a status symbol for men. The opposite is not true."