Being pregnant can sometimes feel like traversing a minefield of advice: You want to do the right thing for your baby and yourself, but conflicting input from physicians, relatives, friends and even total strangers makes it difficult to know exactly what is helpful and what is potentially harmful.
A group of researchers want women to know that when it comes to exercise, there is a strong consensus of benefit for both the mother and developing fetus.
"Within reason, with adequate cautions, it's important for [everyone] to get over this fear," says Alejandro Lucia, a professor of exercise physiology at the European University of Madrid, an author of the viewpoint published Tuesday in JAMA, the journal of the American Medical Association.
According to the American College of Obstetricians and Gynecologists, which updated its recommendations in 2015, women without major medical or obstetric complications should get at least 20 to 30 minutes of moderate-intensity aerobic exercise - enough to get you moving, while still being able to carry on a conversation - on most days of the week. A study published last fall suggests that most women weren't meeting that recommendation, even when active transport, like walking 10 minutes to the store, was included.
For a long time, the belief was that if you weren't already exercising regularly, pregnancy wasn't a good time to start, Lucia says. No longer. Now the evidence suggests that it's actually a good time to begin adding physical activity - it can provide health benefits, and pregnancy may be a time when women are particularly open to positive behavior change. Obviously, though, if you're new to exercise, take it slowly - you can work up to that 20 or 30 minutes.
The authors say physical activity can prevent excessive weight gain, which can complicate the pregnancy and contribute to obesity. A review of existing research published in 2015 by the Cochrane Library found "high-quality evidence" that exercise during pregnancy can help prevent gaining too much weight, and may possibly lower the likelihood of a cesarean section, breathing problems in newborns, maternal hypertension and a baby that is significantly bigger than average. And of course, exercise promotes general cardiovascular and muscular health.
Even many women with chronic high blood pressure, gestational diabetes or who are overweight or obese should be encouraged to exercise, the researchers say.
But there are women who need to be careful with exercise or avoid it. According to the ACOG guidelines, women should avoid aerobic exercise if they have significant heart disease, persistent bleeding in the second or third trimester, severe anemia and risk of premature labor, among other conditions. And certain symptoms, such as contractions or dizziness during exercise, should be checked out ASAP.
The bottom line is that women need to make a plan with their physician, taking into account their exercise history, their health, and the risk of pregnancy complications, says James Pivarnik, a professor of kinesiology and epidemiology at Michigan State University. He wasn't an author of the viewpoint but has conducted research on exercise and pregnancy.
So how much is too much? Moderation is the goal. The worry is that too-intense exercise might lead to dehydration and divert blood flow to the muscles instead of the placenta. So the viewpoint recommends avoiding exercise that makes your heart pump at 90 percent or more of its maximum beats per minute.
It also recommends against long distance running, more from caution than extensive evidence, and against frequent heavy weight lifting, because it may involve what's called the Valsalva maneuver. (That's what you do when you close your mouth, pinch your nose and try to expel air, like you do when you're popping your ears.) ACOG also recommends against contact sports, hot yoga, and exercises done in the supine position, i.e. lying face up, starting in the second trimester.
The upper limits of exercise in trained, elite athletes while pregnant aren't known, Pivarnik notes, nor is the optimal amount in any individual women. After all, there are anecdotal reports of women who complete running races while pregnant and have perfectly healthy babies.
Among the general population and pregnant women specifically, people will respond differently to an exercise program. "But we know if you do the kind of things they're talking about here, the odds are your risk will be lower," he says.
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