Unfortunately, outdated guidelines are still being given out by many obstetric departments and gyms and can still be found on many popular web sites. The previous guidelines were very conservative and based mainly on theory rather than research. New guidelines, although still conservative, are based on new evidence and give women more choices about exercise.

In terms of frequency, The Centres for Disease Control and ACSM recommend the accumulation of moderate physical activity on most if not all days of the week. This moderate exercise would be equivalent to walking at about three to four miles per hour. Higher intensity workouts are considered safe three to four days per week but not recommended two days in a row. Women who exercised before pregnancy can continue throughout. Women who were totally inactive should wait until their second trimester to begin. Most authorities agree that consistency is most important. Women should begin with three times per week and work up to four to five times per week. Anything less than that is inconsistent and could potentially cause harm.

Exercise prescriptions for the pregnant woman should serve to improve cardiovascular and muscular status while also focusing on the specific postural challenges that occur during pregnancy. Just about any aerobic activity is appropriate if comfortable for the client. However, non-weight-bearing exercises are usually most comfortable, especially in later stages of pregnancy. Women who engage in non-weight-bearing activities are more likely to stick with their routines throughout pregnancy. Exercise that poses risk of falling (such as skiing or mountain biking) or trauma to the abdomen, such as in contact sports, is not appropriate due to possible injuries.

Strength training is an important part of a prenatal routine as it supports the woman's changing body. Because of limited research with this population, it is suggested to avoid high resistance and isometric lifting.

The biggest concern is avoiding Valsalva manoeuvre (forced exhalation) and creating internal pressure.

For years, we have limited the motions of pregnant exercisers due to fears about instability of joints and/or imbalance. The theory a woman is more likely to become injured because of ligamentous laxity in joints due to changes in relaxin and estrogens and changes in centre of gravity. Although this should be considered, there is no clear evidence showing higher musculoskeletal injuries. What this means is that most activities are probably safe if they feel comfortable. To be cautious, ballistic or extreme motions should be avoided. As far as stretching goes, it is not suggested to stretch past pre-pregnancy levels.

Many changes will take place in the pregnant woman's body that, if not addressed, will remain thereafter. The kyphotic-lordotic posture (increased curve in upper and lower back) so often seen with pregnancy may remain even after the baby is born if not cared for during and after pregnancy. It is important to strengthen the muscles that are weakened during pregnancy and stretch what is tightened. Follow strength and flexibility programs with these changes in mind.

Even though most workouts can be safe, not all positions are appropriate for the pregnant client. A primary concern is supine exercises (lying on the floor) after the first trimester. Because of the weight of the uterus and baby on the vena cava, there is potential for supine hypotensive syndrome, where the mum and baby are at risk of lack of oxygen and blood flow. Most recent studies show that some activity on the back is safe if done in few minute segments and if the Mum is asymptomatic (not light-headed, dizzy or short of breath). Besides the risk of supine hypotensive syndrome, some abdominal exercises such as traditional crunches could exacerbate a diastasis recti if present.

Some excellent forms of exercise that can be used in prenatal workouts include swimming, yoga, walking, stationary cycling and low impact aerobics classes.

There is perhaps most confusion about intensity for the pregnant client. For many years, ACOG recommended working out at heart rate of no more than 140 bpm. Many obstetric departments and gyms across the country continue to make this recommendation. However, in 2002, ACOG updated this guideline. It is now known that heart rate is a poor indicator of intensity for the pregnant client due to changes in blood volume and pressure. The American College of Sports Medicine recommends any activity that is equivalent to brisk walking.

The guideline of 60 to 70 percent of maximal heart rate or 50 to 60 percent of maximal oxygen uptake appears to be appropriate for most pregnant women who did not engage in regular exercise before pregnancy; the upper part of these ranges should be considered for those who wish to continue to maintain fitness during pregnancy. There is controversy about the threshold for exercise and foetal stress, so it is best to stay within these guidelines.

Most authorities agree that both the talk test and a rating of 3 to 5 on the Borg Scale of Perceived Exertion are appropriate measures of intensity.

The general consensus among experts is that sessions of 30 to 60 minutes of activity are appropriate for prenatal exercise. The two primary concerns in relation to long durations of exercise (over 45 minutes) are energy deficit and thermoregulation. It is of course important to take in necessary calories and nutrition to make up for whatever is expended during exercise. It is no longer appropriate to 'eat for two'

In fact, new recommendations are to eat to appetite. However, it is necessary to make sure you are taking in enough calories if you are exercising, particularly for long sessions. The second concern is in regards to internal temperature. Ideally, pregnant women should exercise in cool, controlled environments. Hydration is key.

The good news is that women who exercise regularly are better able to dissipate heat than women who don't exercise regularly. Most of the research that has been done on this topic is with animals and not humans. Because in truth, we don't know. It is better to be safe and keep mums cool during exercise, particularly during the first trimester.