But with only 27 women holding the chief executive post, the departures of even a few will quickly thin the ranks. Those 27 included Ms. Rosenfeld from Mondelez and Debra Crew, the chief executive of Reynolds American, which is no longer a stand-alone company after being acquired last month by British American Tobacco.

Women continue to make inroads as directors on corporate boards, a critical step toward landing more women in top spots, since those boards select the chief executive. Even so, there are 610 companies in the Russell 3000 — a broad index that seeks to be a benchmark of the United States stock market — that have no women on their boards, according to the research firm Equilar.

“All of this just underscores how tenuous progress for women in the C.E.O. job really is,” said Brande Stellings, a senior vice president at Catalyst, a nonprofit group that pushes for the advancement of women in business. “It’s pretty sad to see we’re struggling to tread water at having women represent 5 percent of C.E.O.s.”

Researchers at Utah State University concluded in a report last year that women were more likely than men to be promoted to the top job of a troubled company. And then, the researchers found, the women “often lacked the support or authority” to make the kind of changes the company needed, leading to shorter tenures.

Female chief executives in their first year on the job were also 34 percent more likely to be targeted by an activist investor agitating for a change in strategy, a separate study by an Arizona State University researcher found. In looking at all chief executive appointments from 2003 to 2013, the researcher found that one in four women had led companies that had landed in the cross hairs of such investors.