Last week, Yahoo’s new chief executive, Marissa Mayer, gave birth to a baby boy. When she was hired in July, late in her second trimester, bloggers and newspaper columnists celebrated the breaking of another pane in the glass ceiling. Pregnant women, it seemed, could be hired for top jobs. Given the many breathless and celebratory “bump watches” in tabloids, it might seem that the stigma around working while pregnant has finally lifted. The birth of Ms. Mayer’s son came only a week after the host of the Emmys, Jimmy Kimmel, introduced the actress Claire Danes with the line, “Our next presenter has a baby in her.” Ms. Danes traversed the stage in a bright yellow dress that emphasized her fertile form.