On the surface, maternity leave is simple: You have a baby, you take time off work to take care of yourself and your baby, and then you go back to work.But now a new breed of working mom is quickly redefining the concept.From Marissa Mayer, who assumed the helm as CEO of Yahoo while six months pregnant, and announced she’d only be taking “a few weeks of leave,” she’d “work through,” to moms who use the “downtime” to launch new businesses, they’ve certainly changed the new mommy landscape.The question is: By working through mat leave—or using that time to alternate between 4 a.m. breast-feeding sessions and hatching a business plan—are they helping or hurting women? And have we officially entered the age of the maternity leave overachiever?MORE FROM LEARNVEST: Does Work-Life Balance Exist?The New Way to ‘Have It All’?Dr. Jennifer Gardner, a pediatrician, used her maternity leave after the birth of her first child, William, to jumpstart an idea she had been sitting on for years: Healthy Kids Company, which educates families on the importance of nutrition.“Maternity leave was actually a great time to start working on it. I knew I was eventually going to return to full-time work as a pediatrician, but while my son was sleeping, I had the free hours necessary to build my website,” she says. ”Starting a company to educate families had always been a passion of mine, but prior to maternity leave, I didn’t really have the time to devote to my idea.”“My maternity leave was my security blanket,” agrees Bridget O’Brien, a former New York City school teacher who used her time away two years ago to found her own PR and event planning firm. “For years, I had been doing event planning free of charge for friends, nonprofits and charities. Working as a public school teacher in New York City is a noble job, but I hated the political aspect behind the scenes.”O’Brien talked the idea through with her husband—she knew she would be happier and that it would create a better environment for their daughter.  ”I would be able to work from home and set my own schedule,” she explains, so she used her mat leave to start amassing clients. After giving birth in January 2010, she officially launched her company in May of that year.MORE FROM LEARNVEST: How to Be a Successful Female EntrepreneurIn fact, O’Brien says that while running her own business can be stressful, she doesn’t resent her even busier schedule. “The day I gave birth to my second child two weeks ago, I was also doing PR for an event in New Jersey with Bravo and the Real Housewives,” she says. “Though I was in labor and handling work on my cell phone, it’s easier because it’s my own company. If I were doing this for someone else, I wouldn’t have been as passionate.”A Dangerous Trend for Moms, Babies … and Women as a Whole?Sure, some women are born overachievers, you might argue—and good for them. But in the wake of Mayer’s announcement, many wondered whether her decision to forgo a traditional maternity leave would put other working women at risk.In the online magazine Slate, one writer opined: “Mayer needs time to emotionally and physically recover … [it’s] nuts to forget that there is a BABY involved here.”Others queried whether her decision would set a bad example for other women looking to juggle motherhood and a career: Namely, would HR departments and bosses then expect more new moms to follow suit—by literally suiting up again mere weeks after giving birth?And why did Mayer—and other ladies who choose to launch when they have an ambitious new project to tackle at home—feel the need?“For some women, working through pregnancy or using the same set of skills used on the job while on leave may be an effort to maintain normalcy,” says Jonathan Alpert, psychotherapist and author of “Be Fearless: Change Your Life in 28 Days.”The brain is craving certainty, says Alpert, so if overachieving is your norm, it may actually be hard to slow down—even with a newborn to contend with. “While working hard may not be advisable from a physical perspective,” he explains, “it may be a positive coping mechanism that helps the mother deal with the uncertainty associated with a baby.”In other words, staying in work mode may allow frazzled new moms—used to a demanding work routine—to maintain some sense of their former selves.Who Creates the Need to Overachieve?Another weighty question: Is our inability to be home with our babies—without refashioning ourselves as CEOs while they nap—something innate in modern-day women, or a response to outside pressure?“Women get stuck in a cycle of fear where they can’t see all the other things that are important in life,” says Shari Goldsmith, a life coach and mental health therapist. “It’s often difficult to be a woman in a workplace, and some fears related to falling behind may be valid.”But there’s also a difference between a natural-born entrepreneur who just happens to have a newborn and someone who’s having a hard time transitioning from her 24/7 attachment to her Blackberry.  Or worrying that being away for that amount of time could cause her to fall behind on the job.“The reality is that women notice and respond to those subtle societal pressures to be better, stronger and smarter, and they make choices accordingly,” says mom of two Samantha Krigsvold. “As a professional woman, breadwinner and mother of two young children, my choice to take an abbreviated maternity leave was absolutely tied to an underlying pressure to prove I could handle it all.”The experts agree: “Women hear over and over again the message that they’re supposed to be able to manage it all—a career and a family. When it comes to taking maternity leave, there are very real fears of being seen as uncompetitive or dispensable,” says Ford Myers, a career coach and author of “Get the Job You Want, Even When No One’s Hiring.”But Isn’t Just Having a Baby Enough?Then again, for many women, wanting to go back to work at all, let alone double down on it during their downtime, just doesn’t compute.Any woman who says she wants to go back to work full-time as soon as possible after giving birth is not being honest with herself,” argues Krigsvold.And what of the need to physically recover? While celebrity magazines trumpeting A-listers’ ability to “lose the baby weight” in record time may be contributing to the rise of the bionic new mom, the fact is birth—whether by a natural delivery or a surgical procedure like a C-section—takes a toll.“I believe every mother deserves proper recovery time, and only the mother can determine what the ‘right’ amount of time is for her,” says Charissa Duncan Mathews, a LearnVest reader based in Tulsa, Oklahoma.MORE FROM LEARNVEST: Meet An Entrepreneur Mom Whose Inventions Paid OffThe bottom line is that there’s no one-size-fits-all policy that suits all new moms. But, says one expert, using your maternity leave as a litmus test can be a good exercise to figure out what you want your new life to look like.How to Make Maternity Leave Work for YouIf you’re the type who’s been sitting on a big business idea, but caught up (for years) in your day-to-day, a whole new routine could be just what it takes to wake up your get-up-and-go.Maternity leave can also provide valuable insight into how your company will respond to your new role as a working mom: “What I tell my clients is that if their employer isn’t going to be understanding early that you need to take maternity leave for your own sake and for the wellbeing of your child, they’re not going to be understanding later on, when it comes to doctors’ appointments, school meetings and more,” says Myers. “So if you do end up losing this job as a result of having taken maternity leave … it probably wouldn’t have ended up working later on, either.”In other words, whatever your perfect version of maternity leave, try to embrace the time you have: “The best advice I ever got was to sit and watch my baby’s eyelashes grow,” says Ainslie Simmonds, LearnVest’s Chief Marketing and Product Officer, and a mother of three. “Because so much changes from day-to-day, it’s just a good way to stay focused, but it can be hard when you’re Type A. I said to the friend who told me that, ‘But I need to be doing something productive!’”“You are,” she replied. “There’s nothing more important than watching a baby grow.”