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Michelle Mottola talks with an expectant mom in the Exercise and Pregnancy Lab at the University of Western Ontario October 28, 2011.GEOFF ROBINS

Amber Miller didn't come anywhere close to winning this year's Chicago Marathon, but she did become the most famous person to run the race. Or perhaps that should be infamous?

Ms. Miller, who lives in the Chicago area, made international headlines for delivering a baby shortly after finishing the race.

Some people reacted with shock and outrage on the Internet. Others were more curious: Is it even safe for a pregnant woman to run a marathon?

Yes, it is, doctors say, at least the way Ms. Miller did it. The 27-year-old new mom sought her doctor's permission and walked the second half of the race, finishing with a time of 6:25:50, minimizing excessive exertion.

Those same doctors will tell you the real cause for concern isn't pregnant women running marathons (not a huge population, after all). The real concern is pregnant woman not getting enough exercise, or sometimes none at all, which can put both women and their babies at risk for a host of problems, including gestational diabetes and pregnancy-induced hypertension.

"The old adages of 'You're pregnant, you should put your feet up' or 'You're pregnant and you can eat for two' is no longer valid, because we now know that's the worst thing you can do," says Michelle Mottola, director of the R. Samuel McLaughlin Foundation – Exercise and Pregnancy Lab at the University of Western Ontario.

It wasn't that long ago physicians were reluctant to prescribe exercise. The Society of Obstetricians and Gynecologists of Canada didn't establish guidelines encouraging pregnant women to exercise until 2003.

"We really didn't have any good evidence based on research studies on exercising women and pregnancy to be able to tell them exactly what was safe," says Gregory Davies, chair of maternal-fetal medicine at Queen's University and one of the principal authors of the SOGC guidelines.

Today, however, research is plentiful and its results – that exercise is not only safe but highly beneficial – need to be more widely promoted, especially when one-quarter of Canadian adults are obese, Dr. Davies says. "Diabetes in pregnancy and high-blood-pressure complications in pregnancy are two of the major problems that we are seeing more of these days."

Obesity doubles the risk for C-sections, doubles the risk for gestational diabetes, doubles the risk of preeclampsia (high blood pressure during pregnancy), doubles their risk of stillbirth. "Every woman should be exercising throughout their pregnancy to their ability," Dr. Davies says.

But there is no research on the potential dangers to pregnant women of more extreme forms of exercise, he says. Ethics committees, quite rightly, are reluctant to green-light experiments that may put a fetus at risk. "What we ask people to do in pregnancy is not to be training toward some excessive event but to be maintaining a healthy lifestyle," Dr. Davies says.

For some very fit women, however, scaling back workouts can prove difficult.

Liz McGurrin, 30, a trainer at StrengthBox, a Toronto gym, recalls doing "some really intense barbell training" when she was first pregnant: "It is possible to get caught up in, 'Yeah, I'm going to be a badass while I'm pregnant' ... and then maybe go past what's going to make you feel good for the rest of the day." It's essential, she says, that pregnant women listen to their bodies.

UWO's Dr. Mottola, who helped develop PARmed-X for Pregnancy – or Physical Activity Readiness Medical Examination, a 1996 guideline for health screening prior to taking part in prenatal fitness classes or exercises –hopes to revise the document as early as next year to tailor guidelines to different fitness levels.

"There are women who are very fit that the guidelines ... might not be strenuous enough for them," she says. (There are also very unfit women who would benefit from more specific guidelines.)

Till then, follow a few rules of thumb, says Karen Nordahl, a professor at the University of British Columbia's faculty of medicine and co-author of Fit to Deliver.

"If you were doing it before you got pregnant, you can do it during your pregnancy," she said. Pregnant women exercising should also be able to pass "the talk test," which requires you to be able to say two sentences without being short of breath.

Women should also use some common sense and avoid any forms of exercise that might cause them abdominal trauma. Snowboarding might be a great workout, but bailing won't be good for your belly, will it?

Sarah Green, a Toronto fitness instructor who has two boys, 3 and 1, kept up her exercise routine during both pregnancies. Hitting the gym in her last trimester didn't raise eyebrows, but people there did address the issue, if only half-jokingly.

"In my last month, a couple of trainers would say, 'No babies today. I'm not delivering a baby on the gym floor,'" Ms. Green says.

Ms. Green kept up her exercise regimen, although not as strenuously. But she wasn't about to experiment, especially when a trainer who didn't know she was pregnant suggested a few martial-arts sessions. "They say don't start anything new, and they definitely mean don't start a jiu jitsu class," she says.

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