Exercise During Pregnancy
Debra Levinson
The recommendations for exercise in pregnancy have evolved with the recently increasing focus on fitness as an adjunct to health and well-being. Both benefits and risks have been hypothesized as resulting from exercise during pregnancy. The pregnant patient can stand to profit with appropriate consideration given to the stage of pregnancy, the prepregnant fitness quotient of the individual, and the current health status of the mother and fetus. However, some adverse perinatal outcomes have been associated with exercise; specifically, the diversion of blood away from the splanchnic bed to the skeletal muscles could deprive the fetus of oxygen and nutrients leading to intrauterine growth retardation or fetal distress (1).
In 2002, the American College of Obstetricians and Gynecologists (ACOG) issued new guidelines for exercise in pregnancy. In summary, the guidelines suggest that in noncomplicated pregnancies, women should continue with the general health recommendations of getting an accumulation of 30 minutes of moderate exercise a day for most or all days of the week. This allows the pregnant woman to continue to benefit from healthy levels of activity. Further, ACOG states participation in most activities is safe, but women should evaluate the risk of potential injuries that may result from contact or falling during any sport or activity. Most activities are safe, but those that pose a risk of abdominal trauma should be avoided. Similarly, scuba diving should be avoided because the baby’s immature circulatory system makes the fetus more susceptible to decompression sickness. Although ACOG feels there is inadequate research on strenuous exercise during pregnancy, athletes who continue to train at a moderate level during an uncomplicated pregnancy are considered safe. Nonstrenuous exercising while breast-feeding during the postpartum period has been shown to reduce postpartum depression. Because it is known that weight loss at a moderate pace does not reduce the milk supply, it is safe to resume exercise during the months of breast-feeding (2).
INITIAL CHANGES OF PREGNANCY
The initial hemodynamic change in pregnancy appears to be an increase in heart rate (3). This commences between 2 and 5 weeks and continues well into the third trimester. Elevation of stroke volume occurs slightly later than the heart rate and continues throughout the second trimester after an augmentation of venous return and a decrease of systemic vascular resistance and afterload. Myocardial contractility is likely to slightly increase.
Structural changes within the heart reflect the volume loading of pregnancy and include dilatation of the valve ring and increase in myocardial thickness. Plasma volume undergoes a 30% to 60% increase during pregnancy. There is also a 20% to 30% increase in red blood cell mass. The increase in blood volume occurs rapidly during the second trimester and lessens near term. During exercise, plasma is filtered out from the capillary bed as a result of increased capillary pressure from working muscles (4). Maximal oxygen uptake and the work rate at the onset of blood lactate accumulation are not significantly altered during the course of a normal pregnancy (4).
Oxygen consumption can increase during pregnancy as the result of an increased number of red blood cells, an increasing tissue mass, and an increase in metabolic rate. Maternal and fetal oxygen consumption climaxes near term and is estimated to be 16% to 30% above nonpregnant values (5).
Regular recreational exercise increases the rate of growth in placental volume in the midtrimester of pregnancy, possibly due to an adaptive response to the intermittent stimulus of a reduction in regional blood flow (6). In addition, recreational exercise performed by wellconditioned women at or above a baseline conditioning level in mid and late pregnancy is normally associated with an increase in fetal heart rate (7). The indication of a diminished blood flow during exercise suggests the
possibility of fetal oxygen supply being lowered and thus the fetal heart rate would be affected more by physical activity in late pregnancy (8). It has been stated that maternal exercise has no effect upon the birth weight, the newborn length, and the placental size, therefore, suggesting that physical activity in pregnancy seems to be neither beneficial nor detrimental to fetal growth (9).
possibility of fetal oxygen supply being lowered and thus the fetal heart rate would be affected more by physical activity in late pregnancy (8). It has been stated that maternal exercise has no effect upon the birth weight, the newborn length, and the placental size, therefore, suggesting that physical activity in pregnancy seems to be neither beneficial nor detrimental to fetal growth (9).
Summarily, effects on the fetus by maternal exercise do not appear to contraindicate physical activity, provided due caution and consideration prevail.
EXERCISE AND PREGNANCY
The safety of the mother and infant is the primary concern in any exercise program. The goal of exercise, both before and during pregnancy as well as during the postpartum period, should be to maintain the highest level of fitness consistent with maximum safety. The potential for maternal and fetal injury is significant because of the musculoskeletal and cardiovascular changes at this time. Therefore, any exercise recommendations should err on the conservative side.
With regard to the professional athlete who is physically well trained, the approach may be to continue training under strict obstetrical observation to avoid a conflict between the patient’s professional needs and the needs of the fetus. Although the athlete may wish to continue to train and compete, it may become extremely difficult for the professional or elite athlete to maintain a level of fitness that will allow her to continue beyond the 20th week of pregnancy (10). All professional athletes should plan to stop active competition between 16 and 20 weeks or earlier if they notice that they are experiencing difficulty (10). The female professional athlete who is under strict observation by her health care provider should expect to have the same pregnancy outcome as any other woman (10). The sole purpose of an exercise program during pregnancy is to maintain physical fitness and to prepare for labor and delivery, and not to challenge the limits of the fetus.
The growth and development of a new life requires the interaction of many of the body’s systems. Exercise requires these complex interactions as well. In fact, pregnancy and exercise “share” certain body systems, including the metabolic system, the circulatory system, the respiratory system, and the musculoskeletal system (11). Because both exercise and pregnancy depend on common systems, they can interact with each other. For example, pregnancy changes the muscular and skeletal systems, which are also basic to the source for locomotion and balance of the individual. Exercise produces heat that can also disturb the developing fetus (11).
PLANNING BEFORE CONCEPTION
Infant mortality rates decrease, not with better birth technology, but with prepregnancy planning, including proper exercise and nutrition. Equally important to eating well is giving the nutrients a chance to get where they are needed. Aerobic activity helps in this regard. When the heart and the circulatory system are stimulated into good performance, healthier organs, stronger connective tissue, and denser bones are built or maintained (12). Also, aerobic activity of the proper type, intensity, duration, and frequency, combined with a diet composed mostly of complex carbohydrates, is the best way to eliminate stored toxins (13).
Guidelines for Prenatal Exercise
The following guidelines are based on the unique physical and physiological conditions that exist during pregnancy. They will outline the general criteria for safety during the development of home exercise programs. This information was compiled from the American College of Obstetricians and Gynecologists Exercise during Pregnancy and the Postnatal Period (ACOG Home Exercise Programs) (12):
Regular exercise at least three times a week is preferable to intermittent activity. Competitive activities should be discouraged. However, in the case of a professional or elite athlete who is already accustomed to training at a high heart rate, it is probable that the pregnant athlete may be able to continue to exercise above the 140 heart rate limit recommended for the general pregnant population (10). Rare cardiovascular complications can also occur in athletes. As a result, warning signs include the appearance of palpitations and tachycardia during rest.
Vigorous exercise should not be performed in hot, humid weather or during a period of febrile illness.
Ballistic movements such as jerky, bouncy motions should be avoided. Exercise should be done on a wooden floor or a tightly carpeted surface to reduce shock and provide a sure footing.
Deep flexion or extension of joints should be avoided because of connective tissue laxity. Activities that require jumping, jarring motions, or rapid changes in direction should be avoided because of joint instability.
Vigorous exercise should be followed by a period of gradually declining activity that includes gentle stationary stretching. Because connective tissue laxity increases the risk of joint injury, stretches should not be taken to the point of maximum resistance.
The pregnant woman’s heart rate should be measured at times of peak activity. Target heart rates and limits established in consultation with the health care provider should not be exceeded.
Care should be taken to gradually rise from the floor to avoid orthostatic hypertension. Some form of activity involving the legs should be continued for a brief period.
Liquids should be taken liberally before, during, and after exercise to prevent dehydration. If necessary, activity should be interrupted to replenish fluids.
Women who have led sedentary lifestyles should begin with physical activity of very low intensity and advance their activity levels very gradually.
Activity should be stopped and the health care provider consulted if any unusual symptoms appear.
As for the pregnant professional athlete, she can consider becoming pregnant while still being competitive. However, she should seek counseling immediately from a health care provider to learn the proper way of balancing the exercise regime with her pregnancy.
Some recommendations for athletes include having a dietary evaluation, a review of desired pregnancy dates, and counseling on potential limitations of pregnancy before conceiving.
In some cases concerning pregnant professional athletes, ovulation induction should be considered. Once pregnant, the professional athlete does not appear to face any problems specific to her professional status. Although few definitive studies exist, the available data indicate that professional athletes are at no greater risk (10).
The predominate maternal risks stem mostly from overuse injuries. Fetal risks are related to hyperthermia, dehydration, and premature labor. Intrauterine growth may occur with a higher frequency. After pregnancy, the athlete can return to competition as soon as she feels ready. Usually, the athlete can resume conditioning activities within 2 to 4 weeks of delivery (10). In considering the average female pregnancy, 12 guidelines should be followed (14):
If you are just starting an exercise program as a way of improving your health during your pregnancy, you should start very slowly and be careful not to over exert yourself.
Listen to your body. Your body will naturally give you signals that it is time to reduce the level of exercise you are performing.
Never exercise to the point of exhaustion or breathlessness. This is a sign that your baby and your body cannot get the oxygen supply they need.
Wear comfortable exercise footwear that gives strong ankle and arch support.
Take frequent breaks, and drink plenty of fluids during exercise.
Avoid exercise in extremely hot weather.
Avoid rocky terrain or unstable ground when running or cycling. Your joints are more lax in pregnancy, and ankle sprains and other injuries may occur.
Contact sports should be avoided during pregnancy.
Weight training should emphasize improving tone, especially in the upper body and abdominal area. Avoid lifting weights above your head and using weights that strain the lower back muscles.
During the second and third trimesters, avoid exercise that involves lying flat on your back as this decreases blood flow to your womb.
Include relaxation and stretching before and after your exercise program.
Eat a healthy diet that includes plenty of fruits, vegetables, and complex carbohydrates.
CONTRAINDICATIONS OR CAUTIONS
The following recommendations are from the 2002 ACOG Guidelines for Absolute Contraindications to Aerobic Exercise During Pregnancy:
Hemodynamically significant heart disease
Restrictive lung disease
Incompetent cervix/cerclage
Multiple gestation at risk for premature labor
Persistent second- or third-trimester bleeding
Placenta previa after 26 weeks of gestation
Premature labor during the current pregnancy
Ruptured membranes
Preeclampsia/pregnancy-induced hypertension
Women with the following signs and symptoms should only exercise with their caregiver’s (health care provider’s) permission in order to comply with the Relative Contraindications to Aerobic Exercise During Pregnancy set forth by the ACOG 2002 guidelines:
Severe anemia
Unevaluated maternal cardiac arrhythmia
Chronic bronchitis
Poorly controlled type 1 diabetes
Extreme morbid obesity
Extreme underweight (BMI < 12)
History of extremely sedentary lifestyle
Intrauterine growth restriction in current pregnancy
Poorly controlled hypertension
Orthopedic limitations
Poorly controlled seizure disorder
Poorly controlled hyperthyroidism
Heavy smoker
Warning Signs and Symptoms to Terminate Exercise While Pregnant
Exercise should stop immediately and the caregiver (health care provider) contacted if the patient experiences any of the following as set forth by the 2002 ACOG guidelines:
Vaginal bleeding
Dyspnea prior to exertion
Dizziness
Headache
Chest pain
Muscle weakness
Calf pain or swelling (need to rule out thrombophlebitis)
Preterm labor
Decreased fetal movement
Amniotic fluid leakage
PHYSIOLOGIC CHANGES DURING PREGNANCY
The physiological changes during pregnancy require certain modifications to any general exercise program. Pregnancy increases maternal blood volume, heart rate, cardiac stroke volume, and, consequently, cardiac output (15).
Normally, blood volume and associated cardiac output increase early in pregnancy (6 to 8 weeks of gestation) and reach a peak increase of 40% to 50% by the middle of the second trimester. Stroke volume and heart rate also increase early in pregnancy and peak by midpregnancy, with stroke volume increasing by as much as 30% and heart rate by 15 to 20 bpm. The total increase in body mass due to pregnancy to be served by this increased cardiac output is only 13%, with the majority of the increase occurring in late pregnancy (15).
Specific maternal cardiovascular alterations help accommodate fetal development. Cardiac output increases 30% to 50% during pregnancy, and the resting oxygen consumption rate increases by 30%. These cardiovascular factors can help facilitate exercise during pregnancy (16).
The increase in cardiac output creates a marked cardiovascular reserve in early pregnancy, when exercise is usually well tolerated. At this stage, some women report an improved exercise tolerance as compared with their prepregnancy level. In late pregnancy, however, cardiovascular reserve decreases as fetal needs increase.
The increase in blood volume is important because many complications of pregnancy, such as premature labor, hypertension, and in utero fetal growth retardation, are associated with relative maternal hypovolemia or failure of plasma volume expansion. The condition, “pregnancy anemia,” usually seen in the second and third trimesters may be a true anemia in some women, but in most it reflects a plasma volume expansion that exceeds the concurrent increase in red cell mass (15).
This process is similar to the pseudoanemia that develops in long-distance athletes because of plasma volume expansion. The pseudoanemia may be substantial evidence for encouraging women to start an exercise program before conception, thus improving cardiac reserve and possibly preventing complications from hypovolemia (15).
During light-to-moderate intensity exercise, the mobilization and use of carbohydrates and fat suddenly increase at least sixfold and remain increased for a variable period of time postexercise (17,18). New tissue growth may be inhibited due to the sudden release of energy.
In addition to the above-cited changes, a pregnant woman experiences respiratory changes, weight gain, changes in energy levels and metabolism, and musculoskeletal changes such as an expanding uterus, which displaces the center of gravity anteriorly, resulting in progressive lumbar lordosis, which in turn, alters balance (15). The concern at this point is an increased susceptibility to injury. Increased lumbar lordosis adversely affects a woman’s ability to exercise during pregnancy.
The impact of exercise can also cause membrane rupture, placental separation, premature labor, direct fetal injury, or umbilical cord entanglement (18). Because of these changes that occur during pregnancy, women may need to avoid or modify strenuous athletic activities and begin exercising conservatively.
Changes in the lumbar lordosis and the onset of anterior pelvic tilt affect a woman’s posture and may make carrying extra weight difficult and painful. Extended periods of walking, even without extra loads, might become difficult, especially after the second trimester. Jogging and other weight-bearing activities can result in increased stress and microshock of the joints (16).
During dynamic exercise, the blood flow in the splanchnic bed decreases in proportion to the increase in heart rate (19) and decreases in circulation to the uterus. The concern here is the lack of nutrients and oxygen available to the embryo or fetus. This could stimulate uterine contractions, causing preterm labor.
Some exercise positions during a dynamic workout may need to be modified. For example, exercise should not be performed in the supine position. When a pregnant woman lies on her back, the weight of the fetus may obstruct the flow of blood back to her heart and head. For this reason, exercise in the supine position has been contraindicated after the fourth month of pregnancy. Symptoms of obstructed blood flow include lightheadedness or dizziness. If a pregnant woman should become light-headed in the supine position, she should be rolled on to her side until she feels better. Then, she should slowly be assisted into an upright position (10).
Women who continue to exercise in a supine position after 4 months into their pregnancy, because they do not “feel” the symptoms of low blood flow to the head, should realize that the blood flow to the fetus may still decrease when in this position. Therefore, the fetus may experience negative effects even though the mother does not (10).
Body temperature and exercise intensity have a direct proportional relationship. During early pregnancy, the obvious concern is that exercise-induced hyperthermia will cause abortion or congenital abnormalities, particularly midline fusion defects of the central nervous system, heart, spine, and urogenital system (17).
Due to hormonal changes and the growing fetus, the body temperature of a pregnant woman usually starts 1 to 2 degrees higher than that of a nonpregnant woman (10). It is extremely important that pregnant exercisers take every precaution against overheating during exercise in a warm environment. Frequent elevation of the body temperature to over 102 degrees in the first trimester may increase the likelihood of neural tube defects in the fetus. Studies associating an increase in body temperature with neural tube defects have dealt with chronic heat exposure, not the heat generated by exercise. However, it is still wise for a pregnant exerciser to be conservative, because the heat generated during exercise can exacerbate chronic heat exposure (17).
The endocrine system’s response to exercise is akin to that of stress. Abrupt hormonal changes take place. Blood levels of catecholamines increase briskly followed by increased secretion of glucagon, endorphin, prolactin, and cortisol (17,18). The concern here is that this response will initiate uterine contractibility and impair other hormonally mediated adaptations to pregnancy (20,21,22).
Although some nonexperimental reports have associated exercise during pregnancy with increased uterine contractions and prematurity and low birth weight, other well-conducted studies using objective measures do not support these claims.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
