Feb. 4, 2011 -- A few weeks ago my 5-year-old daughter was at the kitchen table happily doing an art project, or so I thought. Suddenly she burst into uncontrollable sobs.

I was at my desk frantically trying to send out a work e-mail before dinner and from the sound of her despair I was sure she had stabbed herself with the safety scissors. As I wiped away the tears from her perfect little face, she calmed down enough to explain what was wrong. "Mommy, you were typing, typing, typing and I couldn't take it anymore!" She snapped angrily. "Why won't you draw pictures with me?"

She may as well as stabbed me in the gut with those safety scissors. Every working mother understands exactly what I'm talking about. I know that all mothers, whether they commute to an office every day or not, experience the guilt that comes from not being able to give their children everything they want or because they can't spend enough time with them, but for those of us who are perpetually torn between deadlines and school plays, moments like this are particularly full of self-reproach.

I sometimes believe that my daughter and I are engaged in a Pavlovian experiment of sorts where she was born with a button directly attached to my heart strings. She presses that button over and over again to elicit from me, feelings of love, joy, happiness, awe, pride – and yes, quite frequently, guilt. I do forgive her for pressing the guilt button so often. I don't always respond to it the way she wants because I know it isn't good for her to always get her way or for me to spend every waking minute with her. It's her birthright to press it and my responsibility to react accordingly.

What is harder for me to make peace with is the external blame and recrimination that seems to bombard working mothers on a daily basis. Just today a new study twisted the scissors in a little deeper. It reported a link between the length of maternal employment and childhood obesity. For each year a mother continues to work, University of Chicago investigators found, her child's body mass index (BMI) creeps up a small but statistically significant percentage.

"It amounts to about 1.5 to 2 pounds per year above average, depending on the child's age," Taryn W. Morrissey, Ph.D., one of the report's authors and an assistant professor with the department of public administration and policy at American University, told me. She noted that the difference doesn't make it more likely that a working mother's child will fall into overweight or obese BMI category than any other child, just more likely that the child will be nudged into the higher end of the normal range.

Morrissey seemed like a very smart woman but I didn't really want to talk to her. I was more interested in speaking in one of her co-authors who herself is a working mother. She was out of the country on business.

So with this irony, it was left to Morrissey to explain that the authors found no association between how much time a mother spends at the office and the amount of time her brood spends exercising or parked in front of the TV. Although they didn't find a relationship, they suspect the difference is down to harried, multitasking working mothers resorting more often to fast food and takeout rather than preparing meals at home. The correlation between maternal employment and BMI was strongest among higher income families.

Morrissey stressed that the results of the study are not intended to point of finger of blame at working mothers. Instead, they are supposed to help unravel the mysteries of why our children are getting fatter and fatter, offer health lifestyle suggestions to families, and to light a fire under policymakers to provide affordable, high quality childcare options. These are noble goals which I support.

Still, studies like this make my head hurt. Many working moms feel the same way. When I sent out a Twitter query on this topic, I received over 200 replies in under four hours The majority of women told me that they liked work, had to work, would work even if they didn't have to work, often felt some level of working mother's guilt and dislike studies such as this because they are annoying, counterproductive and don't provide them with any practical solutions.

Interestingly some working mothers told me they aren't guilted by experts, studies or even their kids. Their kryptonite is non-working mothers. "Some traditional stay-at-home moms can't relate to me at all. I am sure that I'm sometimes perceived as a lesser mother because I choose to work," said small business owner and mother of three, Corinne Gregory of Washington State. And Stamford, Conn., working mother of three, Kate Haueisen told me, "I work in a town where there are a lot of stay-at-home moms and I often feel distanced because of the constant comparisons. I'm not always obsessed with the same things, like getting my kid into a certain pre-school."

Personally, I've experienced the opposite. When my daughter was in preschool, our class parent sensed my distress over not being able to participate in planning school events as much as some of the other mothers. "I believe it's the job of the stay-at-home moms to support the working moms and their children," she said to me one day. "It's my pleasure to do a little more so you don't have to kill yourself."

Working mothers have taught me invaluable lessons too, like being the first one to sign up for any volunteer opportunities at school so you can pick the quickest, easiest thing on the list and that having a good hair cut allows you to go three days without showering. Without the support of other mothers of all varieties -- and an amazing husband -- there are some days I couldn't pull off the delicate dance of work and family.

No, it definitely seems that lately it's the science that isn't my friend. Another recent study found that if a mother waits at least nine months before returning to work it has no effect on her child's physical or mental development. I was back on the job three days after giving birth. At the time I was doing a high-paying ghost writing gig for a "celebrity personal trainer" and she had a meltdown when she found out I wasn't available. To this day, my daughter has never thrown a tantrum as snitty as this woman's.

And if it is about science, you could say that being a working mother is akin to the duality of light. You feel like both a wave and a particle, constantly shape shifting between the two existences without ever fully inhabiting either one. When you're at work, half your brain is at home; when you're home half your brain is at work. You sometimes feel like you can never quite remain in one state of matter long enough to finish everything -- or anything.

Despite all my guilt, somehow my daughter is thriving. She is smart, pretty, funny and as healthy as a string bean. She's learning how to read and write, she's a terrific artist – and how many 5-year-olds do you know who can do both a front and back handspring? Besides, I'm a second-generation overworking mother and my siblings and I seemed to be doing OK.

The other night as I was putting her to bed, my daughter told me that she wished I never had to work and that we could play together all day long. "I wish money would just come through the window Mommy," she said.

That's my dream too.

As for the rest of you moms out there, who or what pushes your guilt button? How do you feel about evidence that suggestions your employment affects the health of your children? Post your comments below.