If you are experience contraindications in your pregnancy (eg. persistent bleeding, placenta praevia, pre-eclampsia, pregnancy-induced hypertension and indicators of increased risk of premature labour), then you should be be working closely with your obstetrician and taking care of the development of your baby and physical activity may be limited. HOWEVER, if you are having a healthy pregnancy and have got the “green light” from your doctor to exercise, you certainly should be keeping active!
In the past, pregnant women were discouraged from exercise because of social and cultural biases and unfounded concerns about safety for the fetus, rather than based on scientific evidence. Today, we know that regular exercise during pregnancy can benefit for a woman’s fitness and psychologically well-being, and prevent excessive weight gain in pregnancy, just to name a few.
But just how do we exercise safely in pregnancy? First and foremost, it is important that you are aware of how your body is feeling on a given day. There is a lot of changes the body undergoes each day as pregnancy progress so you may feel great on one day, and horrible on another. Listening to your body and adjust your exercise program is the key to being consistently active throughout your pregnancy.
In a healthy pregnancy free of contraindications, a pregnant woman should aim to be physically active on most, preferably all days of the week. For previously sedentary women and those that are overweight or obese, we can start exercising 3 to 4 days per week on nonconsecutive days to provide a day for recovery between sessions to begin with.
Healthy pregnant women should aim to accumulate 150 to 300 minutes of moderate intensity physical activity each week. Currently, there is no evidence for an upper limit to exercise duration, but it may unwise to extend exercise duration beyond 60 minutes per session, unless the intensity is relatively light. For previously inactive women and those that are overweight or obese, can start with a shorter duration of exercise of 15-20 minutes before slowly building up to 30 minutes.
The precise intensity of exercise prescribed to the pregnant woman will depend on her baseline level of fitness and previous exercise routine. Previously inactive women should be assessed by their doctor prior to starting an exercise program. A woman accustomed to moderate intensity exercise pre-pregnancy can aim to maintain a similar level of intensity during pregnancy, paying attention to her comfort and tolerance levels as pregnancy progresses. There is currently no evidence-based safe upper limit for the intensity of exercise. Pregnant woman can exercise safely by being aware of how their bodies are feeling on a given day and adjusts her exercise based on changes in comfort and tolerance. Special attention should also be paid to ensuring adequate nutrition, hydration and avoidance of overheating.
How to gauge intensity during exercise? The intensity of exercise can be monitored based on the heart rate response to exercise and/or ratings of perceived exertion. Pregnancy-specific heart rate zones equivalent to 60-80% of maximal aerobic capacity have been recommended for normal-weight pregnant women. Previously sedentary women may aim for the lower end of these zones, while those accustomed to regular exercise may work at the upper end of these zones.
For previously inactive overweight or obese women with lower fitness levels, they may aim for heart rate zones of 102 – 124 bpm (for women 20-29 years) or 101 – 120 bpm (for 30-39 years).
A more practical way to monitor the intensity of exercise is the rating of perceived exertion which can be used in combination with heart rate, or alone. A rating of 12-14 on the 6-20 scale reflects exercise of a moderate intensity. For those women with a higher level of fitness that are accustomed to regular vigorous exercise, a rating of 15-16 (equating to “hard”) may be appropriate. Alternatively, the “talk test” is another simple gauge of exercise intensity. The intensity of exercise is considered ‘moderate’ if the woman can comfortably hold a conversation, or ‘vigorous’ if the woman needs to pause for breath during conversation.
In the absence of contraindications, pregnant women are encouraged to participate in both aerobic and strengthening exercises. Aerobic exercises such as walking, stationary cycling or swimming, involve continuous activities that use large muscle groups and elevate the heart and breathing rate. Strengthening exercise can be performed using light weights, body weight or elasticised resistance-bands. Aiming for two sessions of strengthening exercises per week, on nonconsecutive days, women are encouraged to perform strengthening exercises covering the main muscle groups of the body, doing 1 – 2 sets of 12 – 15 repetitions for each exercise. Movements should be controlled and performed with proper breathing technique (i.e. exhalation on exertion). Other sensible precautions include avoiding heavy weight-lifting and activities that involve straining, holding the breath, or that are isometric in nature. Exercises should not be performed lying flat on the back after the first trimester.