Public Science Insights: Tips for Prescribing Exercise to Pregnant Women

Posted Wed, Feb, 22,2017


Before beginning an exercise program during pregnancy, it's important to establish whether the future mother is having a low- or high-risk pregnancy. It is also key to evaluate physical activity levels prior to pregnancy. To evaluate risk level in relation to activity levels, it is very helpful for mothers to visit their healthcare provider and complete a PARmed-X for pregnancy health screening questionnaire. After visiting their health care provider and filling in the PARmed-X for pregnancy questionnaire, the kind of pregnancy and fitness level, whether active or sedentary prior to pregnancy, will be established. If the pregnancy is low-risk, exercise is recommended for the whole pregnancy. Even for women who were sedentary before pregnancy, doing exercise is also beneficial and possible.

Frequency, intensity, time, and type of exercise are the parameters to keep in mind during physical activity. These parameters are known as FITT prescription.

Frequency: If the woman was sedentary before pregnancy, exercising two days a week is a great starting point. After one month, it is suitable to increase to 3-4 days a week. On the other hand, if the woman was active before pregnancy, she should just stick to her regular exercise frequency while keeping the following intensity parameters in mind.

Intensity: Calculating exercise intensity can be challenging. An easy and feasible way to figure out whether the pregnant woman is exercising at correct intensity is to use the Borg's rating of perceived exertion (RPE) scale. This is a scale from 6-20 (6-light exercise, 20-extreme exercise). Women who were sedentary before pregnancy should exercise at a perceived exertion from 13 to 15 on the Borg's Scale, which translates to somewhat hard or challenging yet sustainable effort. For previously active women, exercise intensity should be between 14 and 16 on the scale. Another method for judging intensity would be to use target heart rate zones as listed in PARmed-X for pregnancy recommendations, which are available online. During the third trimester, if the future mother chooses to exercise on an almost daily basis, she should exercise 3 days maximum at moderate to high intensity and any additional days at a low to moderate intensity. Regardless of pre-pregnancy activity levels, future mothers must include rest periods of at least 24 hours. In the third trimester, too much high-intensity exercise can decrease oxygen delivery to the placenta.

Time: For previously sedentary women, it is advisable to begin with sessions that are 20-45 minutes long. They should progressively increase duration to 30-60 minutes over a period of 1-2 months. For women who were active prior to pregnancy, sessions of no more than 60 minutes are recommended. If they would like to train for longer, they must add frequent breaks and ensure that they are not maintaining high-intensity levels for longer than 20-minute intervals. It is important to remember that high-intensity exercise for extended periods should only be performed by previously active women. However, moderate exercise safely provides benefits for all women and their fetuses.

Type: Aerobic and resistance training are the best types of exercise to keep fit during pregnancy because they help to maintain good cardiovascular health and strong muscles.

There are different types of aerobic training, such as walking, swimming, elliptical usage, dancing (low impact), etc. If the future mom ran regularly before getting pregnant, she can continue to run during the second trimester, as long as she feels comfortable. The intensity always has to decrease on runs as pregnancy progresses. Only pregnant women who already know how to swim should choose this activity. This may seem obvious, but starting swimming lessons is not the best option during pregnancy. The recommended duration for aerobic training is 30-60 min, though it will depend on the pregnant woman's fitness level (see time and intensity sections).

Resistance training is also suitable during pregnancy. It can seem challenging and sometimes dangerous, but research widely supports resistance training during pregnancy as a safe and necessary type of exercise. When doing resistance training, focus on big muscle groups (quads, glutes, biceps, chest, etc.). It is best to do about 12 repetitions per set at a moderate load. Pregnant woman should feel that the last rep is challenging, but doable (i.e. no shaking). The recommended duration for doing resistance training is 15-45 min.

The ideal workout should integrate aerobic and resistance training. However, it is not necessary to do both types of training during the same session. Aerobic and strength training can be mixed and matched across workouts throughout the week.

Dr Roldán Reoyo is the author of the recently published paper The Influence of Prenatal Exercise on Offspring Health: A Review, available for download now in Clinical Medicine Insights: Women's Health.

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