Exercise and Pregnancy

Guidelines for Exercise During Pregnancy
The Physiology of Exercise & Pregnancy
Other Useful Links on Pregnancy
Warning Signs

Exercise and pregnancy?  I'm approached regularly by patients who are pregnant or trying to become pregnant, but are concerned that they'll have to curtail their gym or exercise program as they get larger. They ask me "Will exercises harm the baby?", "Can exercise possibly induce premature labor?", "Could I injury myself", "Which exercises should I do?"  Every woman and every pregnancy is completely different. It is therefore critical that you consult your obstetrician before embarking on an exercise program.

Exercise and pregnancy can coexist.
Studies have shown that exercising, besides giving the benefits of maintaining fitness, can also attenuate the symptoms of nausea, fatigue, and back pain. The American College of Obstetrics and Gynecology is now emphasizing the importance of exercise before, during and after pregnancy. Years ago doctors restricted the type of exercise that was safe; today the emphasis is on promoting exercise and pregnancy so long as certain precautions are followed. The exercise you do on the exercise ball can gently work the muscles that help support your back during pregnancy. Also advertised as the "birthing ball", the exercise ball is helpful for easing labor and delivery. Once the baby is born, you can get back into exercising easily using the ball again. The rationale of exercise and pregnancy includes relief of  low back pain, preparation for labor and delivery by increasing strength, endurance, and tolerance for the physical and mental stress.  Posture may be improved and postpartum recovery may be easier and faster.

exercise ball pregnancy warning CAUTION:  Prenatal and postnatal women must get clearance from their physicians before participating in an exercise program.  They must be screened for conditions that would limit their medical, cardiovascular, musculoskeletal, or pregnancy related complications.

Guidelines for Exercise During Pregnancy

The American College of Obstetricians and Gynecologists has the following recommendations regarding exercise and pregnancy - discontinuing exercise under the following circumstances:
  •      Risk factors for preterm labour
  •      Vaginal bleeding
  •      Premature rupture of membranes
  •      Incompetent cervix
  •      Intrauterine growth retardation
  •      Multiple gestation
Pregnant women are best to consult their physician for advice regarding exercise and pregnancy if they have conditions such as
  •     hypertension
  •     gestational diabetes
  •     heart or respiratory condition
  •     history of premature labor
  •     placenta previa
  •     preclampsia

Most experts suggest that you adhere to the guidelines suggested by the acronym FITT:
:    3 to 5 times per week

Intensity:       Moderate intensity
Time:             Maximum of 40 minutes per session
Type:             Low impact aerobic type exercise                            (swimming, walking, bicycling)

Months 1 to 3

If you are were active several months prior to the pregnancy you should remain active but adhere to the FITT guidelines. If you were inactive prior to your pregnancy, hold off exercising for the first three months. Your usual routine is safe. Listen to your body.  Nausea and fatigue may limit your endurance so shorten your routine, reduce its frequency, or change the time of day you exercise. During this period it is still safe to lie on your back. Take this opportunity to strengthen your abdominal musculature as this will weaken very quickly once your abdomen starts to expand. Women with strong abdominal muscles will return to their pre-pregnant figures faster after giving birth, and will suffer less back pain.

Months 4 to 9

Previously active women are able to increase their exercise intensity during the second trimester by 10-15% but within the target zone established by your health care professional. Previously inactive women may begin low impact aerobic activity such as walking, swimming, or cycling.

Changes occur in your body during pregnancy that can affect your ability to exercise while pregnant:

Ligaments: The hormones produced during pregnancy, especially the last trimester, cause the ligaments that support your joints to become more elastic. This causes your joints to lose stability and are therefore at risk for injury. You should avoid sudden bouncing, jerking, or high impact activities. Be careful when exercising if you notice loose or unstable joints.

Balance: As you gain weight, your centre of gravity changes and therefore your posture changes, putting strain on new muscles and ligaments. This can result in altered balance and increased risk of falls. Most exercise ball exercises require some degree of balance so be aware of this and adapt your movements accordingly.

Cardiac Output: Your heart needs to work harder at rest due to the increase in weight, and therefore works even harder when your muscles are demanding increased oxygen. Increases of up to 50% in cardiac output, 15 beats per minute in resting heart rate, and 45% increase in blood volume can occur by the third trimester. The body may divert blood flow from some parts of your body in order to meet the needs of the muscles. It is therefore important not to overdo it. Standing for long periods can reduce placental blood flow so keep changing positions.

Metabolic Rate
Both pregnancy and exercise increase your metabolic rate and therefore core body temperature. It is also know that core temperatures in excess of 102.60F are potentially teratogenic in the first three months. While adaptive changes that occur to the woman's body during pregnancy help dissipate this extra heat, it is still prudent to maintain adequate hydration and avoid exercising in hot or humid environments. To avoid compromising fetal growth, caloric intake should be adequate to offset the combined needs of pregnancy and exercise (typically an extra 300 calories a day).

Pregnancy and exercise both increase the bodies need for oxygen. Oxygen requirements during pregnancy are greater therefore limiting your ability to perform high intensity activities. You need to heed signs of fatigue and stop workouts short of exhaustion to reduce the potential risk of hypoglycemia. Sessions for recreational athletes are best limited to 45 minutes.
Increasing abdominal size: The weight of the growing fetus will compress the inferior vena cava and hence affect blood return to the heart possibly causing your blood pressure to drop when lying in the supine position. This can disrupt the oxygen supply to the fetus.It is obvious then to avoid the exercise ball exercises that require you to be in the supine position. Prone abdominal hollowing, and  pelvic tilts in standing can be used to activate the abdominal muscles.

 The increase in abdominal size puts extra strain on
 the supporting back muscles so avoid those more
 advanced exercises such as
  •                 push ups
  •                 double leg raises
  •                 full sit ups
  •                 jumping, hopping or skipping
  •                 quick dance moves

Supportive bras and back braces are now available to assist you with these changes as you exercise. Exercise and pregnancy can go hand in hand.

The Physiology of Exercise and Pregnancy

Because multiple organ systems are involved in creating the optimal environment for the fetus, the physiology of gestation is complex. The impact of exercise and pregnancy and its physiologic variables has been studied, but there is no agreement about some aspects of cardiopulmonary and metabolic response.  Studies involving human subjects have been inconsistent, partly because of differences in study design, exercise regimens, and the fitness level of the participants. Prospective, adequately controlled studies of humans are few, so animal models have been used to elucidate the interaction of exercise and pregnancy.

The energy cost of pregnancy is higher than that of the non pregnant state by an average of 300 k.calories per day, exercise also increases caloric expenditure. So pregnant women who exercise need to consume enough calories to meet these increased needs. Physically active pregnant women should eat enough to satisfy their appetite, preferable a diet rich in complex carbohydrates. Weight should be monitored to be sure that gains are steady and adequate.

Hyperthermia during pregnancy is a potential teratogenic risk to the fetus. Some experts are concerned that pregnant women who exercise may increase their body temperatures to dangerous levels. However, studies show that exercise does not cause the same level of increase in body temperature in pregnant women as it does in non-pregnant women. This may be because the work intensity achieved by pregnant women is not high enough to cause such a rise. Pregnant women also may be better able to cool themselves with changes in regional blood flow.

Women who choose to mix exercise and pregnancy must drink adequate fluids. They should drink up to a pint of liquid before exercising, and a cup of liquid every 20 minutes during exercise. Even if they are not thirsty after exercise, they should drink enough to replenish lost fluids( 1-2 litres of fluids per hour may be lost through sweating)

Pregnant  women also should be cautioned against exercising when the weather is hot and/or humid, or when they have a fever. In general, the higher the air temperature, the lower the humidity, the concern with exercise and pregnancy must be to avoid heat injury. For example, if the air temperature is above 80 degrees Fahrenheit, humidity should be no higher than 50%. Also, it's safer to exercise before 8 am and after 6 pm.

The weight of the growing fetus increases lumbar lordosis, moving the centre of gravity to the pelvis and causing a compensatory increase in cervical spine flexion. Balance may become precarious as movements are modified to accommodate these changes.

Pregnant women should be told that exercises involving sudden changes in body position carry a greater risk of falls. Sports with the potential for abdominal trauma, such as surfing, horseback riding, or trampoline exercise, should be avoided.

Ligaments relax as connective tissue softens in response to hormone changes early in pregnancy. This increased joint mobility may facilitate delivery of the baby, but it also may make women more vulnerable to sports induced injury during exercise and pregnancy. Softening of  connective tissue and increased lordosis is also related to the back pain that often occurs in pregnancy. Adequate warm up is important to avoid sprains. Pregnant women who do resistance exercise should use light weights so that joints are not excessively loaded.

Water retention in the third trimester may reduce mobility at the wrists and ankles and lead to carpal tunnel syndrome, causing sensory changes and muscle weakness. Activities involving strength and agility of the hands such as tennis and skiing may make pregnant women more injury prone during exercise and pregnancy.

Cardiac output increases by 30-50% during pregnancy, peaking in the second trimester. It is variable in the third trimester but decreases when the woman is in the seated or supine position because of decreased venous return. Both components of cardiac output -heart rate and stroke volume - increase. The stroke volume is greatly affected by an increase in heart size, with left ventricular volume enlarging considerably by term. The responses to exercise of both stroke volume and cardiac output are significantly increased during pregnancy. An increase in blood volume parallels the increase in cardiac output to some degree. The volume of plasma component of blood increases up to 50%, but red cell volume increases only up to 20%, resulting in the relative anemia of pregnancy, with hematocrit dropping from a normal of 40% to about 35%. This is similar to the pseudo anemia seen in endurance athletes and may be more significant in pregnant endurance athletes. Oxygen distribution to tissues is not affected by this drop in hematocrit as seen by the decreased arteriovenous oxygen difference.

The resting heart rate rises in the first weeks of pregnancy by about 7 beats per minute and plateaus after 32 weeks at a rate approximately 16 beats per minute faster than the prepregnancy rate. Studies of fetal growth and development show that increases or decreases in fetal heart rate during exercise are transient and produce no deleterious effects.

The mean arterial blood pressure of a pregnant woman drops reaching its lowest value at mid pregnancy and returning to near prepregnancy levels at term. Systolic blood pressure changes very little, so women have an increased pulse pressure and throbbing pulse. Peripheral resistance also decreases, allowing an increased cardiac output with a drop in blood pressure.

Cardiac output and blood pressure may vary with changes in body position. When a pregnant woman is in the spine position, the uterus rests on the vertebral column and can compress the inferior vena cava and abdominal aorta, causing a drop in cardiac output and resultant hypotension.

The decreased venous return raises the concern of whether certain positions assumed during exercise compromise blood flow to the fetus. Exercises performed when a woman in in the supine position are not recommended after the first trimester. Motionless standing can cause an even greater drop in cardiac output and should be avoided when possible. Blood to skeletal muscles and the fetus is in parallel circulation, and a potential problem is that blood may be shunted toward exercising muscles and away from the fetus. Animal studies show that although uterine blood flow transiently decreases during exercise and pregnancy, uterine oxygen extraction increases markedly during pregnancy, and fetal and placental oxygen levels are maintained.

 Hemoconcentration during exercise occurs to a greater degree in pregnancy than in the nonpregnant state, enhancing oxygen delivery. Basal oxygen consumption increases during pregnancy by about 40 ml/min, with the fetus, placenta, heart, and kidneys consuming the most oxygen. Pregnant women increase ventilation by breathing more deeply rather than more frequently. Although the diaphragm rises with the increasing size of the uterus, the total lung capacity and vital capacity change very little.  Tidal volume increases up to 40% as the woman breathes more deeply, and residual volume and expiratory reserve volume become smaller to compensate. This results in a smaller oxygen reserve in the lungs at the end of a quiet expiration, and less ability to withstand apnea. For this reason, scuba diving and sprinting are not recommended during pregnancy.

Pregnant women respond differently to physical exercise than do nonpregnant women. They also show greater variability in response to the physiologic challenge of exercise. The increase in body weight and reduced efficiency of oxygen utilization requires a greater oxygen cost for any given weight bearing exercise. The reasons for this greater oxygen cost are not entirely understood. Some studies indicate that women who exercise during pregnancy may have a training effect, increasing their aerobic capacity.

Many women experience a decline in exercise performance during pregnancy and are unable to maintain high levels of aerobic exercise. This decrease in exercise tolerance is due in part to a lower cardiopulmonary reserve, but factors such as fatigue, nausea and vomiting and changes in body configuration may also contribute. There is some indication that non weight-bearing exercises such as swimming and cycling are better tolerated by pregnant women.

Exercise during pregnancy maintains muscle tone, strength, and endurance and it may protect against back pain and other discomforts. Subjective benefits such as improved mood, energy level and self-image have been reported. Women who exercise regularly at a moderate intensity can maintain cardiorespiratory fitness during pregnancy and reduce the risk of postpartum obesity. Most evidence suggests that moderate exercise during normal pregnancy has no adverse or beneficial effects on maternal weight gain, length of gestation, length of labour, infant birth weight or APGAR scores. One must be wary when exercising while pregnant because there are flaws in the studies available about the effects of exercise on pregnancy and a lack of studies using human subjects.

All pregnant women need a medical and obstetric examination before they begin an exercise program. Contraindications to exercise and pregnancy should be ruled out, and women with conditions such as chronic hypertension or active thyroid, cardiac, vascular or pulmonary disease need a careful evaluation to determine if they are candidates for regular exercise.

Other Useful Links for information on Exercise during Pregnancy

For the American College of Obstetricians and Gynecologists' Educational Brochure on exercise and pregnancy click on the following link:

For Guidelines of the American College of Obstetricians and Gynecologists for exercise and pregnancy and the postpartum period click on the following link:
 British Medical Journal

The Exercise ball is sometimes referred to as the birth ball or birthing ball. For more information on the birth ball click on the following link:
Birth Ball

For sport specific guidelines for exercise and pregnancy click on the following link:
Sport Specific Guidelines for Exercise during Pregnancy

exercise during pregnancy