What signal is Marissa Mayer giving to Yahoo employees?

Editor's note: Stephanie Coontz teaches family studies at Evergreen State College in Olympia, Washington, and co-chairs the Council on Contemporary Families. Her most recent book is "A Strange Stirring: The Feminine Mystique and American Women at the Dawn of the 1960s."

(CNN) -- The news that Yahoo knowingly chose a pregnant woman as its new CEO has rightly been heralded by working women and their allies as another hole in the glass ceiling. Marissa Mayer, until now a top executive at Google, reports that when she told Yahoo's board of directors that she and her husband are expecting their first child in October, no one expressed any second thoughts about hiring her. The lack of reaction "showed their evolved thinking," she said.

But Mayer's next sentence immediately squashed any illusions that her presence at Yahoo foreshadows any change in corporate America's 24/7 work culture. "My maternity leave," she told reporters, "will be a few weeks long, and I'll work throughout it."

Mayer's assurance that having a child will require so little adjustment in her work schedule has led many women to worry that she is naive about the physical and emotional price she will pay for taking so little time to recuperate and bond with her new baby. Others express concern that her child will suffer for her decision.

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Stephanie Coontz

These worries are mostly groundless. The real problem with Mayer's pledge to take only a few weeks off and work right through it has little to do with her own welfare or her child's. It is the message this sends to her employees about the expected work culture at Yahoo.

Mayer will probably do just fine returning to work so early. Top executives have much more flexibility than the lower-level employees they rely on to be at the office bright and early, set things up for the day, reschedule appointments when necessary, run errands and deliver needed papers if they are working off-site. They can also afford to hire live-in nannies so that they never need to scramble to cover gaps or breakdowns in child care coverage. Mayer's husband, a tech investor, has similar flexibility.

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Mayer's son is also likely to turn out fine, assuming that she and her husband are even moderately competent parents. On average, while very short maternity leaves do increase the risk of insecure attachment between mother and child, most mothers bond successfully, even with short leaves. Psychologists Philip and Carolyn Cowan, authors of "When Partners Become Parents" and leading experts in what makes for effective child outcomes, note that kids of working mothers do well when women are happy with their jobs, have good child care arrangements, and fathers actively participate in making these work-family choices.

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In fact, a major predictor of whether a woman will be warm and responsive to her child, avoiding the bouts of depression that are one of the most serious threats to effective parenting, is whether she is happy about the work choices she makes. A woman with Mayer's work ethic would probably be a less effective parent if she felt compelled to stay home when she wanted to work.

But Mayer's insistence that she will get back to work so quickly sets a bad precedent for Yahoo's lower-level employees, mothers and fathers, who do not have the job flexibility and cannot afford the extensive social support and backup systems that Mayer and her husband will be able to construct.

Ellen Galinsky, president of the Families and Work Institute, argues that the personal work-life choices of top leaders in a workplace are as important as their formal work-life programs and policies in shaping expectations about what is and is not acceptable. Leaders who take little time off for family create a work culture that inhibits lower-level employees from asking for any work-family rearrangements they may need.

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It's great that corporate leaders no longer assume a high-powered female employee will lose her brain, drive and work commitment when she gets pregnant. And I admire Mayer for feeling free to set a high priority upon her work commitments without succumbing to the guilt that weighs down so many working moms. But it might be better for the rest of us working parents, who don't have the same resources and support systems, if she would take a longer leave and maintain a dignified silence about just how many work hours she puts in during it.

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The opinions expressed in this commentary are solely those of Stephanie Coontz.