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Expecting Questions About Exercise and Pregnancy?

David Araujo, MD

THE PHYSICIAN AND SPORTSMEDICINE - VOL 25 - NO. 4 - APRIL 97


In Brief: The appropriateness of various forms of exercise during pregnancy is controversial. Numerous physiologic and anatomic adaptations to pregnancy affect a woman's ability to exercise and her body's response to exercise. Placental blood flow, the potential for hyperthermia and trauma, changes in coordination and balance, body position during exercise, increased nutritional requirements, and the potential for back and pelvic pain must all be considered in light of each woman's particular exercise program. Clinical guidelines for recommending exercise or participation in competitive sports during pregnancy are provided.

Pregnant women come from diverse exercise backgrounds; some are recreational athletes, some are fitness enthusiasts, while others are competitive athletes. To appropriately counsel these patients, it is important to understand how exercise affects the physiologic adaptations that occur during pregnancy. Participation in athletic activities usually must be modified during pregnancy; continued participation in competitive sports is of special concern.

The following two cases illustrate some of the concerns that must be addressed when caring for an athletic woman who becomes pregnant.

Case 1

A 30-year-old woman presented for prenatal care at 12 to 14 weeks gestation. Her medical history was unremarkable, and there was no family history of genetic diseases. She was a fitness enthusiast and adhered to a weight training program. A typical workout schedule was 1 hour of weight training three times per week. Each day she focused her workout on a different part of the body: upper body training with free weights and a universal gym; abdominal and biceps muscle training with sit-ups, an inclined board for leg raises, and free weights; and leg training with the universal gym, stair climber, and stationary bicycle. She performed each exercise in three sets of 12 to 15 repetitions; this workout was followed by 10 minutes of exercise on a stair climbing machine. The patient asked if she could continue her exercise routine during pregnancy.

It was recommended that she reduce the intensity and duration of exercise as she approached 20 weeks gestation; that she continue to reduce the intensity and eventually eliminate the abdominal exercises; and that she maintain fluid intake and prevent overheating throughout the pregnancy.

Her pregnancy was uneventful and resulted in a 20-lb weight gain. A healthy boy was delivered vaginally after approximately 5 hours of labor.

Case 2

A 21-year-old woman presented for prenatal care at approximately 10 weeks gestation. Her medical history was unremarkable. She was a varsity college basketball player and wanted to continue to play competitively, but also wished to ensure the well-being of her unborn child.

The patient was counseled about the risk of abdominal trauma from continued play and the difficulty she would encounter with balance and coordination as her pregnancy progressed. She chose to withdraw from competitive athletics for the duration of her pregnancy. Her pregnancy was uneventful.

She changed providers and delivered at a different hospital, but it is known that she delivered at term.

Changes During Pregnancy

Physiologic changes occur in the cardiovascular, respiratory, musculoskeletal, and gastrointestinal system and affect the maternal response to exercise. The anatomic changes of pregnancy alter balance, flexibility, and coordination.

Cardiovascular. The heart adapts to the increased demands placed on it by the enlarging uterus and growing fetus by increasing cardiac output 30% to 50% over the prepregnancy level. However, when a pregnant woman is supine, cardiac output decreases beyond the nonpregnant baseline, especially after 28 to 32 weeks gestation. The resting heart rate increases by up to 7 beats per minute in the first trimester and by 15 beats per minute in the second and third trimesters.

Another significant circulatory adaptation is an increase in blood volume of 35% to 45% over the prepregnant state. This increased volume is partially offset by an increase in venous capacitance, so that blood pressure is not increased and may actually decrease in the second trimester. The increase in venous capacitance contributes to vasodilation at the skin, which increases heat loss—an adaptation that may help to prevent hyperthermia during exercise. A physiologic anemia of pregnancy results from a relatively greater increase in plasma volume than red cell mass. It has been noted that those patients with preeclampsia do not exhibit this physiologic anemia, and it has been theorized that this increase in plasma volume may be associated with a better pregnancy outcome.

Performance in endurance athletic activities may improve during the first 12 to 15 weeks of pregnancy, before the increase in body weight and uterine size precludes involvement in competitive athletics. This increase in performance probably results from the increased blood volume and red blood cell mass, which function as a type of in vivo "blood doping" that can increase oxygen-carrying capacity (1).

Respiratory. The respiratory system is affected anatomically by the enlarging uterus and physiologically by hormonal changes. Uterine enlargement can elevate the diaphragm by as much as 4 cm, which increases the anterior-posterior chest diameter but reduces functional residual capacity. A resting hyperventilation occurs in response to increased plasma progesterone, which results in resting hypocapnia and a concomitant maternal alkalosis, thought to protect against fetal acidosis. Resting oxygen consumption is also increased by up to 20%.

Gastrointestinal. The gastrointestinal system is affected anatomically by the enlarging uterus and physiologically by increased plasma progesterone, a smooth muscle relaxant. The combined effects of these changes contribute to constipation and a slowing of gastrointestinal motility. The increase in progesterone also promotes relaxation of the lower esophageal sphincter, which leads to increased gastric reflux manifested by symptoms of heartburn.

Musculoskeletal. Multiple adaptations of the musculoskeletal system can affect the ability to exercise. The anterior displacement of the enlarging uterus changes the woman's center of gravity and exaggerates normal lumbar lordosis. The increase in hormone levels, especially progesterone, promotes ligament and joint laxity, which is needed to bring about the pelvic relaxation and symphyseal widening that permit vaginal delivery. The enlarging breasts also affect the woman's center of gravity, and their increased weight can contribute to upper back and shoulder pain. The center of gravity shifts inferiorly and posteriorly to the lumbar spine because of the enlarging uterus.

Physiologic Issues

Exercising during pregnancy is of concern to athletic women because of the fear that such activity will harm their unborn children. In several situations this may be true; however, well-conducted double-blind trials of exercise during pregnancy are rare because of the ethical concerns inherent in asking pregnant women to engage in activities with unknown effects on their unborn children. Most recommendations that physicians make regarding exercise during pregnancy are based on extrapolation of the results of animal studies or on empirical observations of pregnant athletic women.

Placental blood flow. Changes in uteroplacental blood flow probably occur with exercise; however, this phenomenon is relatively difficult to study. The placenta is a volume-dependent organ, which means that changes in blood volume have a greater effect on placental blood flow to the fetus than do changes in sympathetic tone that alter blood pressure in the systemic circulation. There are no autoregulatory mechanisms to alter blood pressure in the uteroplacental unit. Studies (2) of pregnant women exercising in controlled settings have demonstrated fetal tachycardia, though this response is variable. Some have suggested that exercise-induced fetal tachycardia is a sign of fetal distress (3,4) and diminished uteroplacental blood flow during exercise (5). Others (6) feel that the flow of blood through the placenta remains unchanged, but that the flow of blood to the pregnant uterus is reduced, as it is for any organ during exercise. Still other researchers believe that fetal tachycardia is primarily a response to circulating maternal catecholamines during exercise. Fetal tachycardia during maternal exercise may also result from increased maternal core temperature. As a result of this controversy, fetal tachycardia is not considered a reliable marker of fetal distress in exercising pregnant women.

Hyperthermia. During exercise, maternal hyperthermia should be avoided. This recommendation is based on the supposition that hyperthermia can be teratogenic, although causality has not been proven. Some authors have suggested that hyperthermia during pregnancy causes neural tube defects, because of observations that women who experience a significant febrile illness in the first trimester give birth to a greater number of infants with congenital defects than women who have not had such an illness (7,8). However, it is not clear whether the defects result from the fever or from a direct toxic effect of the infecting agent. Animal studies (9,10) have demonstrated an increased incidence of fetal malformations after deliberate elevation of maternal temperature. What is clearly known is that dehydration and hyperthermia resulting from strenuous exercise have detrimental effects on the mother (hypovolemia) and on uteroplacental perfusion. Hypovolemia may result from overheating during exercise and has been associated with preterm labor.

Coordination. The balance skills required for athletic activities such as gymnastics, ice skating, skiing, golf, and tennis are affected by the enlarging uterus and the resulting changes in the center of gravity. Athletic activities that require significant balance skills will need to be modified for women in their second and third trimesters of pregnancy. Participation in sports such as gymnastics where there is the potential for falls may need to be eliminated. Joint laxity and an increase in the interstitial fluid volume, especially in the weight-bearing joints, lead to decreased kinesthetic sensation and diminished coordination. All of these changes probably increase the risk of ligament strains and bony trauma, such as ankle or wrist fractures during a fall.

Trauma. Participation in competitive sports that pose a risk of trauma, such as basketball, should only be undertaken with the pregnant patient's full understanding that abdominal trauma to a pregnant uterus carries the risk of placental abruption, premature labor, and possibly, preterm delivery. These concerns are most relevant to a woman who is at more than 20 weeks gestation, when the uterus has become an abdominal organ. Before 12 to 15 weeks, the uterus is relatively protected by the bony structures of the pelvis. The period of 15 to 20 weeks gestation is considered a gray zone for participation in competitive sports, and the possible risks should be fully discussed with the athlete and her coach.

Body position. The position required to perform various types of exercise is also of concern during pregnancy. Supine exercise, such as some aerobic exercises, sit-ups, and weight lifting on a bench press machine, should be avoided, as in this position the pregnant uterus compresses the inferior vena cava, compromising venous return to the heart. In the exercising woman, this can decrease blood flow to other areas of the body, such as the brain and muscles, possibly leading to syncope. This compressive effect is greatest after the uterus has become an abdominal organ, usually after 20 weeks gestation.

Nutrition. Pregnancy increases calorie requirements by approximately 150 kcal per day in the first two trimesters, and by 300 kcal per day in the third trimester. Exercise during pregnancy further increases calorie requirements, and nutrition supplementation should take into account these increased needs. Vitamin and iron supplements are generally recommended for pregnant women, though no double-blind studies of routine vitamin or iron supplementation for pregnant women have been conducted. An exception to this is folic acid, which at a dose of at least 1 mg per day prior to pregnancy and during the first trimester has reduced the incidence of neural tube defects (11).

Back and pelvic pain. Exercise during pregnancy may exacerbate back and pelvic pain. It is estimated that at least 50% of pregnant women experience some degree of back pain (see "Back Pain and Pregnancy: Active Management Strategies," July 1996). Sacroiliitis and facet joint inflammation may be exacerbated by strenuous exercise. Symphyseal separation and symphysitis may result from weight-bearing exercise. Osteitis pubis and bony resorption about the symphysis may result from any weight-bearing exercise and cause the symphyseal gap to widen.

What Do Guidelines Say?

Over the past 10 years, controversy has arisen regarding recommendations for exercise during pregnancy. In 120215, the American College of Obstetricians and Gynecologists (ACOG) published guidelines (12) based on the consensus opinion of a panel of obstetricians. Some of the recommendations, based on empirical observation, recommended exercise of no longer than 15 minutes, a maternal heart rate not to exceed 140 beats per minute, and a core temperature not to exceed 38°C (100.4°F). These guidelines were designed to ensure the safety of the majority of pregnant women, but were later thought to be too restrictive for most trained athletes.

In 1994, ACOG published another document (13) on exercise during pregnancy and the postpartum period. The previous guidelines on heart rate and duration of exercise were eliminated, and the recommendation was modified to read that most women "can exercise moderately to maintain cardiorespiratory and muscular fitness throughout pregnancy and the postpartum period."

Sufficient evidence exists that women who are trained athletes probably will not experience adverse outcomes at a higher intensity of exercise; however, current recommendations do not support more vigorous exercise regimens. In a recent epidemiologic study (14) conducted by the Missouri Department of Health, 2,828 women who had recently given birth were surveyed on several topics regarding their pregnancy. This study determined that the mother's level of exercise, the number of hours she worked, and the specific activities she undertook while pregnant, such as carrying heavy loads, did not increase the risk of fetal demise or low birth weight.

On the basis of a review of the literature, primary care physicians can individualize their exercise advice for pregnant patients using the safety tips presented in table 1—with the understanding that this topic remains controversial.


Table 1. Exercise Safety Tips for Pregnant Women
  1. Fluid intake during and after exercise should be adequate to prevent dehydration and hypovolemia.
  2. Clothing worn during exercise should allow for adequate ventilation and prevention of hyperthermia.
  3. Exercise during febrile illness is contraindicated.
  4. Supine exercise should be avoided, especially in the third trimester.
  5. Exercises that require repetitive bouncing and jerky movements should be avoided, especially in the third trimester.
  6. Recommended exercise regimens should emphasize low-impact activities, such as stationary bicycling, swimming, walking, and low-impact aerobics.
  7. Activities that involve potential low-oxygen states, such as scuba diving and mountain climbing, are contraindicated.
  8. The exercising pregnant woman should be encouraged to follow a diet that emphasizes complex carbohydrates to replace muscle glycogen lost during exercise, thereby minimizing the risk of fetal ketosis.
  9. Participation in competitive team sports is acceptable in the first 15 weeks of pregnancy if the woman understands that there are potential but unproved risks for fetal loss from pelvic trauma, abdominal trauma, or both.
  10. Exercises requiring significant use of Valsalva's maneuver, such as weight lifting, should be avoided, especially in the third trimester.

The presence of some medical conditions is an absolute contraindication to exercise during pregnancy. Patients who have congestive heart failure, valvular heart disease associated with an increased risk of heart failure due to volume overload, severe hypertensive disease, uterine bleeding, premature rupture of membranes, or incompetent cervix should not be allowed to exercise. Other medical conditions, such as anemia, thyroid disease, medication-controlled diabetes, breech presentation in the third trimester, multiple gestation, essential hypertension, or excessive weight gain or loss carry a relative contraindication to exercise; the advisability of exercise in such cases must be determined on an individual basis.

Active Involvement for Patients

Exercise during pregnancy remains a somewhat controversial issue that has not been addressed by well-conducted double-blind studies. Recommendations for the trained athlete usually involve a modification of the type and intensity of exercise to avoid dehydration, hypovolemia, hypotension, and potential trauma to the developing fetus. The woman must be informed of the potential risks associated with exercise so that she can participate in the decision regarding continued involvement in athletic activities.

References

  1. Clapp JF III, Capeless E: The VO2 max of recreational athletes before and after pregnancy. Med Sci Sports Exerc 1991;23(10):1128-1133
  2. Hon EH, Wohlgemuth R: The electronic evaluation of fetal heart rate: the effect of maternal exercise. Am J Obstet Gynecol 1961;81(Feb):361-371
  3. Stembera ZK, Hodr J: The "exercise test" as early diagnostic aid for fetal distress, in Horsky J, Stembera ZK (eds): Intrauterine Dangers to the Fetus. New York City, Exerpta Medica Foundation, 1967
  4. Pokorny J, Rous J: The effect of mother's work on fetal heart sounds, in Horsky J, Stembera ZK (eds): Intrauterine Dangers to the Fetus. New York City, Exerpta Medica Foundation, 1967
  5. Pomerance JJ, Gluck L, Lynch VA: Maternal exercise as a screening test for uteroplacental insufficiency. Obstet Gynecol 1974;44(Sept):383-387
  6. Morrow RJ, Ritchie JW, Bull SB: Fetal and maternal hemodynamic responses to exercise in pregnancy assessed by Doppler ultrasonography. Am J Obstet Gynecol 120219;160:138-140
  7. Milunsky A, Ulcickas M, Rothman KJ, et al: Maternal heat exposure and neural tube defects. JAMA 1992;268(7):882-885
  8. Lynberg MC, Khoury MJ, Lu X, et al: Maternal flu, fever, and the risk of neural tube defects: a population-based case-control study. Am J Epidemiol 1994;140(3):244-255
  9. Shiota K: Induction of neural tube defects and skeletal malformations in mice following brief hyperthermia in utero. Biol Neonate 120218;53(2):86-97
  10. Sellers MJ, Perkins-Cole KJ: Hyperthermia and neural tube defects of the curly-tail mouse. J Craniofac Genet Dev Biol 120217;7(4):321-330
  11. Wald NJ: Folic acid and neural tube defects: the current evidence and implications for prevention. Ciba Found Symp 1994;181:192-208
  12. ACOG Home Exercise Programs: Exercise During Pregnancy and the Postnatal Period. Washington, DC, American College of Obstetricians and Gynecologists, 120215
  13. Exercise during pregnancy and the postpartum period. ACOG Technical Bulletin Number 189—February 1994. Int J Gynaecol Obstet 1994;45(1):65-70
  14. Schramm WF, Stockbauer JW, Hoffman HJ: Exercise, employment, other daily activities, and adverse pregnancy outcomes. Am J Epidemiol 1996;143(3):211-218

Suggested Readings

  • Artal R: Exercise and pregnancy. Clin Sports Med 1992;11(2):363-377
  • Bell R, O'Neill M: Exercise and pregnancy: a review. Birth 1994; 21(2):85-95
  • Clapp JF III: A clinical approach to exercise during pregnancy. Clin Sports Med 1994;13(2):443-458
  • Goodlin RC, Buckley KK: Maternal exercise. Clin Sports Med 120214; 3(4):881-893
  • Jarski RW, Trippett DL: The risks and benefits of exercise during pregnancy. J Fam Pract 1990;30(2):185-189
  • Heckman JD, Sassard R: Musculoskeletal considerations in pregnancy. J Bone Joint Surg (Am) 1994;76(11):1720-1730
  • Sady SP, Carpenter MW: Aerobic exercise during pregnancy: special considerations. Sports Med 120219;7(6):357-375
  • Snyder JL: Aerobic exercise during pregnancy. J Am Board Fam Pract 1990;3(1):50-53
  • Pivarnik JM, Mauer MB, Ayres NA, et al: Effects of chronic exercise on blood volume expansion and hematologic indices during pregnancy. Obstet Gynecol 1994;83(2):265-269
  • Warren MP: Exercise in women: effects on reproductive system and pregnancy. Clin Sports Med 1991;10(1):131-139

Dr Araujo is director of the Family Practice Residency Program at the Sutter Merced Medical Center in Merced, California, and a clinical faculty member in the Department of Family Practice program at the University of California at Davis. He is an advisory faculty member for Advanced Life Support in Obstetrics (ALSO), a program of the American Academy of Family Physicians. Address correspondence to David Araujo, MD, Merced Family Practice Residency, 315 E 13th St, Merced, CA 95340; e-mail to [email protected].


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