Why exercise during pregnancy?
Some women wish to exercise during pregnancy because they were doing regular exercise before they became pregnant and wish to continue. Other women who have not done regular exercise before, see pregnancy as a good time to start a regular exercise program.
EFFECTS ON THE MOTHER OF EXERCISE DURING PREGNANCY
When we exercise there is an increase in the amount of blood pumped around the body each minute, up to 3 times the resting level. During pregnancy there is an increase in the amount of blood pumped by the heart in the resting state, (about 1½ times the non-pregnant level) so there is a smaller margin left for an increase during exercise. This means that pregnant women should reduce the intensity of exercise to a level 25-30% lower than before pregnancy, limiting their peak heart rate to 140 beats per minute.
Pregnancy is associated with an increase in weight of 12-14kg and a very obvious change in body shape! There are also changes in posture, walk and joints. These changes result in greater difficulty with balance, more likelihood of joint pain and an increased risk of injury. Pregnant women should avoid sports which involve sudden movements an d changes of direction. A supportive sports bra may reduce breast discomfort during vigorous exercise.
Extra energy is required during pregnancy. The extra energy needs are met by an increase in food intake, a decrease in energy use, or both. The best measure of appropriate energy balance during pregnancy is adequate weight gain. It is important to time snacks to avoid a drop in blood glucose during and after exercise (have some fruit or a sandwich one hour before exercise).
There is extra heat generated during pregnancy from the baby and placenta and from extra work done by maternal organs. The extra heat must be eliminated by the mother by an increase in blood flow to the skin and by sweating. Exercise is also associated with increased heat production so exercise during pregnancy represents an even greater challenge to the mother’s temperature control.
EFFECTS ON THE FETUS OF EXERCISE DURING PREGNANCY
Maternal injury – fall and blows to the maternal abdomen
Especially after first trimester, there is a small risk that maternal injury will be associated with fetal distress or (rarely) death due to premature separation of the placenta or premature labour. Pregnant women should avoid sports where there is a significant risk of falls (such as horse riding, snow skiing, water skiing) or violent body contact (such as basketball and hockey).
Increase in maternal temperature
Exercise during pregnancy represents a challenge to the mother’s temperature control. An increase in body temperature early in pregnancy may cause a small increase in the risk of having a baby with a malformation. In order to avoid increasing maternal temperature above 38°C, women should limit periods of strenuous exercise to 15-20 minutes, avoid exercising in hot, humid conditions and maintain their level of hydration by drinking plenty of fluids. Maintaining a high fluid intake may be associated with the need to pass urine frequently. Pregnant women who are exercising in water should ensure that the water temperature does not exceed 28-30°C and should avoid hot spa pools and saunas. The most
important time for a woman to avoid hyperthermia is very early in pregnancy, when she may not realize she is pregnant, so women who MAY be pregnant or who are trying to become pregnant should also follow these guidelines.
Recent research has shown that women who continue frequent strenuous exercise sessions into late pregnancy have babies with reduced birthweight. The reduced birthweight may be due to early delivery, reduced fetal growth, or both.
Pregnant women should not exercise maximally (they should reduce exercise intensity by 25-30%) and should always follow exercise with a cool-down period.
It is recommended that women restrict their sessions of strenuous exercise to no more than 4 times weekly.
AFTER THE BIRTH
During the first three months after birth, women are advised to observe the exercise guidelines for pregnancy. Swimming should be avoided until any bleeding has stopped (usually about four weeks after delivery). Women who do strenuous exercise while breastfeeding should ensure that they have adequate rest, fluids and food intake.