BALTIMORE -- Her Asics laced up and her water bottle at her side, Meredith Dobrosielski stepped onto the treadmill for a robust half-hour walk.
For the Towson, Md., runner, this wasn't just any trip to the gym. The session took place in a lab at Johns Hopkins Bayview Medical Center in Baltimore. And each step offered information on the impact of exercise on her fetus. Dobrosielski is about 8 months' pregnant.
Doctors expect the information collected to fill in some gaps in the data on how much pounding is OK for a developing baby. Eventually, they hope to be able to develop personalized workout schedules for women in different states of fitness.
"We do know that not only can exercise be done, it should be done," said Dr. Andrew J. Satin, professor and vice chairman of the department of gynecology and obstetrics for the Hopkins School of Medicine. "But the level of fitness should impact the individual's prescription."
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Not too long ago, doctors used to tell all women not to exercise when they became pregnant, but that advice has changed, said Satin and Dr. Linda Szymanski, a fellow in maternal fetal medicine helping conduct the research. But there still are little data about what is too much for the elite athlete verses the couch potato and those in between. Satin said much is based on "opinion and common sense."
They believe research is limited because doctors fear testing pregnant women. But nine months into the study, there have been no adverse reactions. Over time, the doctors plan to measure the impact on fetuses; partner with biomedical engineers to develop new ways to monitor the fetus, perhaps wirelessly during exercise; and collect long-term data on the pregnancy outcomes.
Enough but not too much
Doctors and groups such as the American College of Obstetricians and Gynecologists and the American Pregnancy Association give blanket advice to pregnant women: Get 30 minutes of exercise a day.
Potential benefits include improvement in general health and a decreased chance of gestational diabetes and hypertension, and easier labor, delivery and recovery.
But the advice is based on recommendations for pregnant people who aren't pregnant -- and it is filled with notes of caution for those who are just starting and those with certain conditions. The college suggests seeing a doctor first, starting slowly and stopping when there is pain or bleeding -- advice Satin doesn't dispute.
He added that doctors do know that driving up a heart rate and maintaining it there for too long can cut off blood flow to the fetus. Getting overheated and dehydrated are also problems. Joints also can become lax and balance may be off, so some exercises should be avoided, such as street biking late in pregnancy. Contact sports, horseback riding and downhill skiing also may cause injury from blows or falls.
But he and others say not everyone has gotten the message that exercise is beneficial.
It was a big change in 2008 when physical guidelines were published for Americans, including pregnant women, said James Pivarnik, who works with the sports medicine college and is professor of kinesiology and epidemiology and director of the Center for Physical Activity and Health at Michigan State University.
He said the guidelines do indicate "that the elite runner can continue doing what she is doing for a bit, provided her healthcare provider is in the loop, and that she has no warning signs or other issues." But he said "boutique" recommendations are hard with so many possible circumstances; he is now looking at how much weightlifting is good for pregnant women.
What to know
Szymanski said the incomplete data have only confused the message to pregnant women. Outdated information and myths perpetuated by the Internet still mean that many women who had been exercising -- up to a quarter by some accounts -- stop because they fear they will harm their babies, the doctors said.
Satin says that as long as jogging is comfortable, runners can keep doing it. Stationary bikes and running in a pool also are good exercises, Satin said. And walking is safe for nearly everyone. The fetuses are not "flipping and flopping," he said. In fact, the entire uterus is moving with the exercise motion, buoying the fetus.
Dobrosielski, who is about to have her second child, said she decided to participate in the study because she wanted to help other women. She's been running "forever" and played field hockey in high school and college. An ankle injury stopped her from running after four months, but every day she runs in a pool, does yoga, lifts weights or rides a stationary bike.
"It's a special population, and there's so little time for study," she said. "I felt comfortable exercising, and I knew when I needed to stop. I think it's important for all women to exercise and maybe this research will convince them to do that."