Marissa Mayer in 2008. Yahoo! announced July 16, 2012 it had named her chief executive, making her among the most prominent women in technology and corporate America. (OLIVER LANG/AFP/GETTY IMAGES)

The decision to hire Mayer — Google’s first female engineer, who reportedly had been running about a quarter of the company — sends a great message to women (and about Yahoo, which could use some good PR.) It may even have a trickle-down effect, at a minimum inside Mayer’s new shop.

How big a deal is this? According to TechCrunch, this is a first for a CEO of a publicly-traded Fortune 500 company. And here’s how much things have changed in the 16 years ago since my twins were born: Not long after I went back to the office — initially working three days a week, though that quickly crept up to four and then five — one of my female colleagues informed me that she and others in the office felt I should no longer be “allowed” to write for Page One; that wouldn’t be fair to reporters without children, she said, who had not gotten to take any leave — and who were expected to work 7 days a week.

“She the People” writer Diana Reese remembers those days, too — and recalls interviewing for a job in journalism when she was single and four months pregnant in 1991: “I was skinny then and not showing much, so I safety-pinned my suit skirt closed, made sure my jacket hid my little baby bump, and lied through my teeth. Everyone I knew cautioned me not to say a word about being pregnant. The general consensus was that they would never even interview me if they knew.”

The Post’s Nikita Stewart says she, too, hid the fact that she was pregnant when she interviewed for a reporting job at The Star-Ledger 13 years ago, revealing it only after they’d made her a firm offer “because I feared they would never give me a chance” otherwise.

She got the job, showed up right after her maternity leave from her prior employer — “that was also a trick” — and has been kicking journalistic derriere ever since. But we shouldn’t have to pull “tricks” to have kids and also support them doing work we’re good at.

Marissa Mayer poses at Google's Mountain View, California headquarters, in this February 24, 2009 photo. (NOAH BERGER/REUTERS)

How “having it all’’ ever became the impossible dream I’m not sure, but if all of our work/life challenges were behind us, Anne-Marie Slaughter’s recent Atlantic cover piece, “Why Women Still Can’t Have It All,’’ would not have become the best-read story in the magazine’s history. Slaughter, the former director of policy planning for the State Department, left after two years to spend more time with her teenagers and return to her old teaching job at Princeton — hardly a nothing post.

Monday night on The Colbert Report, Slaughter stipulated that in even trying to have — maybe not it all, but important bits of it — it makes a big darn difference if you’re wealthy and have hot- and cold-running nannies. (You bet it does, and in what area of life is that not true?)

Obviously, it’s because Mayer is so highly regarded — as my Post colleague Roxanne Roberts said, Yahoo needed her a lot more than she needed them — that she can get a deal like this, one that makes a moot point of the glass ceiling and knocks out the wall where the nursery adjoining her office will be.

A pregnant friend of mine worries that Mayer’s stated intention to take only a few weeks off after giving birth — and even then, she’ll be working from home — might suggest that women who take a real maternity leave are slackers.

But if she can turn around Yahoo while breastfeeding, she will have pulled off what a succession of CEOs before her couldn’t manage — and if she doesn’t, I dare to hope they won’t blame it on her baby.