The Centers for Disease Control and Prevention and the American College of Sports Medicine (CDC and ACSM) have recommended 30 minutes or more of moderate intensity physical activity on most, and preferably all, days of the week for the general population.
But what if I’m pregnant?
In 2002, the American College of Obstetricians and Gynecologists (ACOG) published exercise guidelines for pregnancy. They suggested that despite the fact that pregnancy is associated with profound anatomical and physiological changes, in the absence of medical or obstetric contraindications, 30 minutes or more of moderate exercise a day on most, if not all, days of the week is also recommended for pregnant women. This will allow them to get the same associated health benefits from being physically active during pregnancy as before pregnancy. Exercise maintains fitness, strengthens muscles, and boosts circulation. It also prevents varicose veins and constipation, improves emotional well-being, and helps prevent excessive weight gain. However, these recommendations did not define ‘moderate intensity’ or the specific amount of weekly caloric expenditure from physical activity required for pregnant women to maximize the benefits of being physically active.
As a former dancer, I love the thrill of moving my body to the music I love. I got used to moving around, and I try to get some physical activity every day. Once I got pregnant I asked myself: How safe it is to keep my normal exercise routine? Will it be harmful for the baby? Should I make any modification?
Researchers in Denmark examined the relationship between physical exercise during pregnancy and the risk of preterm birth. Self-reported data on physical exercise during pregnancy were collected prospectively for 87,232 singleton pregnancies included in the Danish National Birth Cohort between 1996 and 2002. Results showed a reduced risk of preterm birth among the almost 40% of women who engaged in some kind of exercise during pregnancy in comparison with non-exercisers. The type of exercise did not affect the association, and the results were not altered when the degree of preterm birth was taken into account (Juhl et al., 2008). Another group of researchers conducted a prospective observational investigation at the Naval Medical Center, in San Diego, California. They evaluated the influence of exercise, by level of activity, on maternal and perinatal outcome in a large low-risk healthy obstetric population of working women. Based on their findings, exercise does not appear to affect antenatal, intrapartum, or postpartum complications, even after evaluating these women for confounding variables such as maternal age, race, gravidity, parity, maternal illness, height, pre-pregnancy weight, weight gain during the pregnancy, prior preterm delivery, smoking, and stress (Magann et al., 2002). These findings do not contradict current recommendations.
However, current ACOG guidelines are based on studies published before or during 2002. According to a recent review, healthy pregnant women can benefit from exercising at a moderate intensity for a longer duration than recommended in the current ACOG guidelines. Researchers found that increasing physical activity energy expenditure to a minimum of 16 metabolic equivalent task (MET) hours per week, or preferably 28 MET hours per week, and increasing exercise intensity to ≥60% of heart rate reserve during pregnancy, reduces the risk of gestational diabetes mellitus and perhaps hypertensive disorders of pregnancy, such as gestational hypertension and pre-eclampsia, compared with less vigorous exercise. To achieve the target expenditure of 28 MET hours per week, one could walk at 3.2 km (nearly 2 miles) per hour for 11.2 hours per week (2.5 METs, light intensity), or preferably exercise on a stationary bicycle for 4.7 hours per week (~6–7 METs, vigorous intensity). The more vigorous the exercise, the less total time of exercise is required per week, resulting in ≥60% reduction in total exercise time compared with light intensity exercise. They also found that light muscle strengthening performed over the second and third trimester of pregnancy has minimal effects on a newborn infant’s body size and overall health (Zavorsky & Longo, 2011).
Please consult with your doctor on how to safely exercise during pregnancy
It is not advisable to start a demanding regimen during pregnancy, though. Excessive or improper activity can be dangerous to the woman and the baby. Every pregnant woman should be carefully evaluated before recommendations on physical activity participation during pregnancy are made. We should also take into account that certain obstetric complications may develop in pregnant women regardless of the previous level of fitness, which could preclude them from continuing to exercise safely during pregnancy (Artal & O’Toole, 2003). All active pregnant women should be examined periodically to assess the effects of their exercise programs on the developing fetus, so that adjustments can be made if necessary. Work with your doctor to make sure you and your baby are not at risk for possible complications derived from your workout plan.
Next time: We'll share some information about safe exercises during pregnancy
2. Magann EF, Evans SF, Weitz B, Newnham J. Antepartum, intrapartum, and neonatal significance of exercise on healthy low-risk pregnant working women. Obstetr & Gynecol. 2002;99(3):466-472.
3. Zavorsky GS, Longo LD. Exercise Guidelines in Pregnancy. New Perspectives. Sports Med. 2011; 41 (5): 345-360.