Exercise During Pregnancy

Whether prescribing exercise to teenage children, the elderly, cardiac rehabilitation patients or expectant mothers, exercise is warranted if the benefits outweigh the potential risks. Fitness instructors should therefore be aware of the potential benefits and risks of exercise during pregnancy.

Given the scope of this manual it is not appropriate for us to examine in detail the physiological events associated with pregnancy, as a result, this section will be confined largely to the exercise prescription guidelines which should be followed during that time.

During pregnancy it is wise not to start a new exercise program without medical approval and supervision. The most common advice to those who are not accustomed to regular exercise is that they should wait until after the birth to start a training program. Similarly it is not wise to increase the intensity of an existing exercise program during pregnancy.

Instructors should take particular care to ensure that expectant mothers avoid thermoregulatory stress. During exercise a greater proportion of the cardiac output is distributed to the working muscles and the subcutaneous vessels leaving less for the foetus. Furthermore, the fetal temperature rises along with the mothers core temperature. Should the mother become dehydrated as a result of prolonged and intense exercise the fetal blood flow may be further compromised so expectant mothers should be encouraged to drink regularly and to dress appropriately.

For the reasons outlined above, pregnant women should also avoid excessive durations of continuous activity. Some authorities have suggested that multi-peak or interval classes may be more appropriate than constant intensity classes. The American College of Obstetricians and Gynecologists recommends, as a rough guide, that pregnant women's heart rates should not exceed 140 beats per minute. Obviously such a guideline does not take into account variations in fitness levels but it suggests that the anaerobic threshold is an appropriate maximum exercise intensity.

In the later stages of pregnancy some mothers will be more comfortable performing weight-supported activities. However, weight-bearing activity is not contra-indicated unless it causes discomfort or injury.

Because of hormonal changes (the release of the hormones relaxin and estrogen) which occur during the later half of pregnancy, it is important to minimize the use of ballistic movements, especially those performed through an extreme range of motion. Relaxin and estrogen act to loosen the connective tissues (ligaments) of the pelvis in order that the baby can move through the birth canal with less resistance. However, these hormones also affect joints other than those in the pelvis, resulting in an increased risk of joint injuries in the later stages of pregnancy.

The womb is situated in front of the inferior vena cava, which is the largest vein in the body. Therefore, whilst lying on her back the pregnant woman may partially reduce the venous return to the heart. In order to minimize the risk of fainting or dizziness the mother should avoid lying in the supine position for more than two to three minutes.

The linea alba, the connective tissue which connects the two halves of the rectus abdominus, sometimes splits or separates during pregnancy. Whilst this condition is not painful it should be avoided if possible. Some authorities suggest that women should perform abdominal exercises with their hands placed over the stomach. It is hard to imagine how this would prevent splitting but it may increase the mothers awareness of any problems should they arise.

The most obvious benefit of exercising during pregnancy is the maintenance of fitness and body composition.

Whilst it is important not to make generalizations in this area some authorities suggest that labor is often shorter and less complicated for women who are physically active throughout pregnancy. This observation may, however, be complicated by the fact that only healthy women already engaged in fitness programs are encouraged to exercise during pregnancy.

Who should not exercise during pregnancy?

Whilst individual cases require the consideration of the personal physician some general guidelines can be given.
Women who should not exercise during pregnancy include;

a. Those with a history of three or more spontaneous miscarriages.
b. Those with a history of premature labor.
c. Those with heart disease or pregnancy induced hypertension.
d. Those whose pregnancies exhibit complications such as fetal growth retardation or placenta praevia.

source: Fit and Pregnant: The Pregnant Woman's Guide To Exercise by Joan Marie Butler