Practical Exercise Advice During Pregnancy
Guidelines for Active and Inactive Women
Amanda K. Weiss Kelly, MD
Practice Essentials Series Editors:
THE PHYSICIAN AND SPORTSMEDICINE - VOL 33 - NO. 6 - JUNE 2021
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In Brief: Many women enjoy regular exercise as a part of a healthy lifestyle and may wish to continue exercising after they become pregnant. Some previously sedentary women may want to start an exercise program during pregnancy. Primary care and sports medicine physicians should understand the contraindications (eg, hypertension, diabetes, placenta previa, preeclampsia) and the concerns about exercise during pregnancy (eg, fetal nutrition, risk of preterm labor) and be able to offer reasonable guidelines to women who wish to start or continue exercise during pregnancy. Most non-weight-bearing exercises (eg, swimming, stationary bicycling) and walking are safe for pregnant women, beginning with 15 minutes of exercise three times a week and progressing as tolerated.
In the past, exercise during pregnancy was commonly discouraged. Concerns were initiated by the observation that women in occupations requiring physical work or prolonged standing tended to deliver early and have small-for-gestational-age babies.1,2 Other reports contradicted these observations, implying that strenuous activity alone may not affect fetal outcome.3,4 The current scientific literature suggests that exercise is safe for women experiencing uncomplicated pregnancies. In fact, many positive effects of exercise during pregnancy have been noted. As more women who exercise regularly before pregnancy wish to continue to exercise during pregnancy, physicians should be prepared to offer exercise guidelines to pregnant women.
Based on observations, theoretical concerns arose that maternal exercise could result in physiologic and metabolic changes that might lead to fetal malformations or poor fetal growth.
Increased temperature. Early investigations demonstrated an increase in neural tube defects in offspring born to women who regularly used hot tubs during pregnancy.5 This led to concerns that increases in body temperature during exercise may cause similar defects. In active nonpregnant women, exercise can elevate body temperatures above 102.5°F (39.2°C), a level felt to have teratogenic potential.6
In studies monitoring core temperatures of pregnant women during exercise,7-9 body temperatures did not reach potentially teratogenic levels. In addition, one small prospective controlled study10 compared birth outcomes of exercising women with sedentary women and did not find an increased risk of fetal anomaly or early pregnancy loss. Another small study11 did not find any increased risk for fetal anomaly in exercising women. To our knowledge, however, no randomized controlled trials evaluating the risk of early fetal loss or anomaly in exercising women are available for review.
Uterine blood flow. Another concern is that decreased splanchnic blood flow associated with exercise could compromise uterine or umbilical artery blood flow, leading to fetal distress or decreased delivery of oxygen and nutrients to the growing fetus.12 Using Doppler ultrasound to evaluate the uteroplacental and umbilical circulations during exercise, several investigators demonstrated decreases in uterine artery flow without changes in umbilical artery flow,13-15 but a recent study16 documented no changes in either uterine or umbilical artery perfusion.
To evaluate fetal distress during maternal exercise, investigators have monitored fetal heart rate tracings immediately after exercise. Many have demonstrated increased fetal heart rates during maternal exercise without changes in other heart tracings8,14,15,17-19; whether this change in fetal heart rate represents distress, a response to maternal catecholamine release, or some other response is not yet clear.
One large study20 found that 11% of 258 fetuses experienced tachycardia, 1% of fetuses had decelerations, and 1% had bradycardia in response to maternal exercise. Two smaller studies21,22 also found fetal bradycardia in 14% to 16% of subjects (3 of 22 and 2 of 12). The episodes of bradycardia resolved within 2 minutes in the study by Kennelly et al,20 and bradycardia of this magnitude seems unlikely to result in fetal hypoxia. Studies are needed to evaluate the effects of exercise on repeated occasions in regularly exercising women.
Some of the physiologic changes of the cardiovascular system associated with pregnancy, such as increased maternal blood volume, heart rate and cardiac output, and decreased systemic vascular resistance, may act to lessen exercise-related decreases in splanchnic blood flow.23,24 In addition, increases in blood volume are accentuated in women who exercised during pregnancy compared with sedentary women.25,26
Fetal nutrient supply. Another concern has been that glucose use by exercising muscles could limit nutrient availability to the growing fetus. While some studies27 have demonstrated a fall in maternal glucose levels during exercise and some data show that exercise significantly reduces neonatal fat mass,28 few investigators have noted differences in fetal growth when comparing exercising and nonexercising pregnant women.29 This may be due to increases in glucose delivery after exercise and increases in placental size found in physically active pregnant women.30,31 Maternal weight gain during pregnancy in exercising women may be similar to or less than their sedentary counterparts.32,33 However, even in women who gain less weight, the amount of weight gained remains within an acceptable range.34
Preterm labor. Concerns that exercise may lead to uterine contractions and premature labor are based on the theory that decreased blood flow to the uterus during exercise may lead to contractions or that the hormonal response to exercise, including the catecholamine response, may induce uterine contractions and premature delivery. While some women subjectively note contractions during exercise, tocodynamometry immediately after exercise has failed to demonstrate increased uterine activity. Also, prospective studies have not found increased rates of preterm delivery in pregnant women who exercise.28,35,36 In fact, studies35,37 have found that exercising women are at decreased risk for preterm delivery.
Positive Effects of Exercise
Moderate physical activity during normal pregnancy has been associated with many beneficial effects. Some of the less desirable aspects of pregnancy, such as physical discomfort, the effect of weight gain on self-image, complications of labor and delivery, and gestational diabetes mellitus may be alleviated by exercise.
Musculoskeletal and pelvic discomfort. Many hormonal and anatomic changes affect the musculoskeletal system during pregnancy. Musculoskeletal discomfort during pregnancy, especially back pain, is common. The increased weight and lordosis associated with pregnancy make maintenance of an upright posture more difficult and increase the workload of the muscles in the lower back.38 Women who exercise during pregnancy tend to have fewer musculoskeletal complaints, including low-back pain, compared with sedentary women.33,38,39 While pregnancy does not seem to worsen musculoskeletal conditions such as scoliosis, spondylolisthesis, or spondylolysis, we have no information available about the effects of pregnancy and exercise on these conditions.38
Pelvic pain is another common complaint during pregnancy, and it may be caused by ligamentous laxity induced by the pregnancy-related hormones relaxin and progesterone.38 The effects of aerobic exercise on pregnancy-related pelvic pain have not been well studied, but water aerobics may have some benefit in reducing pelvic and low-back pain in pregnancy.40 Also, some groups have had success reducing low-back and pelvic pain with specific strengthening exercises and physical therapy, though the exercise programs have been heterogeneous and the results mixed.41-45 Some women who have rheumatologic musculoskeletal conditions, such as rheumatoid and idiopathic juvenile arthritis, may experience remission with pregnancy, which could allow them to exercise more comfortably.38
Self-image, depression, and weight loss. Women who exercise tend to report better self-image and fewer depressive symptoms, both during and after pregnancy, than inactive women.33,39 Compared with sedentary women, women who exercise during pregnancy gain similar amounts of weight or less weight and may have a smaller amount of subcutaneous fat deposition.29,34 But, as mentioned earlier, exercising women do tend to gain enough weight to support a healthy pregnancy. Physically active women tend to return to prepregnancy weights faster than do sedentary women.29 Of note, exercise in the postpartum period has not been found to adversely affect the new mother, lactation, or infant growth.24,46,47
Gestation, labor, and delivery. Women who exercise during pregnancy do not seem have an increased risk for preterm labor or delivery; but in one study,28 exercising women delivered about 7 days earlier than nonexercisers. Most investigators have not found that exercise during pregnancy has any effect on the course of labor and delivery, but some28,48 have found shorter active or second stages of labor in women who exercise. Women who exercise during pregnancy are not at increased risk for operative delivery and may even have lower risk than their sedentary counterparts.28,33,39,48-50
Gestational diabetes. Exercise during pregnancy may be useful in preventing and treating gestational diabetes mellitus. Several investigators have demonstrated improved glucose tolerance and reduced insulin requirements in women with gestational diabetes who participate in low-intensity aerobic exercise or resistance exercise.51-54 Even better results have been noted with higher-intensity exercise programs.55 The optimal amount and intensity level of exercise required to best prevent and control gestational diabetes is still being investigated, but the American Diabetes Association supports the use of exercise as part of therapy.
Exercise Effects on the Fetus and Newborn
The risk of adverse effects of exercise on the growth and development, delivery, and viability of neonates born to exercising mothers appears to be minimal.
Fetal size. Most studies find that fetal size is not affected by exercise training during pregnancy. However, results from available studies are quite variable, with some showing no difference,29 some showing increased30,31 and some showing decreased28 weight in infants born to physically active women. When decreased fetal weight has been noted, it has been in women exercising at high intensity for 1 to 2.5 hours a day during pregnancy; however, the difference in newborn weight was almost entirely accounted for in fat mass, and not head circumference, length, or lean body mass.28
Fetal distress during delivery. Few studies comparing fetal distress during delivery of exercising and sedentary women are available, but the neonates of exercising women may have decreased incidence of abnormal heart rate patterns and meconium-stained amniotic fluid.28 Appearance, pulse, grimace, activity, and respiration (APGAR) scores of infants born to exercising mothers are similar to or higher than those born to nonexercising mothers.28,33,39
Neonatal behavior. One study examining neonatal behavior in infants of exercising women56 found that the infants quiet more easily after stimulation in the newborn period, perhaps as a result of learned fetal responses to intermittent arousal. In addition, the infants born to physically active women demonstrated increased alertness compared with infants born to nonexercising mothers.
General Exercise Guidelines
Some exercise recommendations can be applied to all women, regardless of levels of activity before pregnancy (see the Patient Adviser, "Exercising for Two: Steps for a Healthy, Active Pregnancy"). The Canadian Society for Exercise Physiology provides forms for comprehensive physical activity readiness medical examinations (PARmed-X for Pregnancy; available at https://csep.ca/forms.asp).
Pregnant women should be instructed to modify exercise intensity based on symptoms.6 The "talk test" (ie, not too short of breath to carry on a conversation while exercising) and the Borg relative perceived exertion scale57 (figure 1) are simple to explain to patients and are recommended by The Society of Obstetricians and Gynaecologists of Canada.58 Exertion perceived as somewhat hard (Borg level 12 to 14) is recommended for pregnant women.
Caloric intake for all pregnant women should be adjusted to compensate for energy expended during exercise. Pregnancy requires an increase of 300 kcal/day,6 and women who exercise during pregnancy will require additional calories to replace those used during exercise. In addition, pregnant women should be advised to drink plenty of fluids before, during, and after exercise to ensure adequate hydration to avoid hypovolemia and decreased cardiac output.
After the first trimester, exercises performed in the supine position or exercise requiring prolonged motionless standing should be avoided, because these positions can obstruct venous return and are associated with decreased cardiac output and hypotension.59
All women should be advised that certain pregnancy complications preclude safe exercise (table 1). Also, women with significant heart disease or restrictive lung disease should refrain from exercise during pregnancy.1 Women with other significant medical conditions, such as chronic hypertension, thyroid disease, or less serious cardiovascular or pulmonary disease, should be thoroughly evaluated before beginning an exercise program.6
Other relative contraindications for exercise during pregnancy are listed in table 2. Women experiencing these complications should be closely evaluated and followed up if they wish to exercise during pregnancy. All pregnant women should be counseled to discontinue exercise until seen by a physician if they experience significant shortness of breath, vaginal bleeding, dizziness, headache, chest pain, amniotic fluid leakage, or decreased fetal movement during exercise.1,6 Women with signs or symptoms of deep venous thrombosis, such as significant calf pain and swelling or muscle weakness, should not exercise until this possibility has been ruled out.1
It may also be prudent to counsel women to recognize that groin or anterior thigh pain with weight bearing may represent transient osteoporosis of the hip. While this is relatively uncommon, it is seen more commonly in pregnant women than in others, and the condition may actually be underdiagnosed.38 Because the risk of complications following femoral neck fracture is significant, pregnant women who exercise should be advised to seek medical attention if these symptoms occur.
Guidelines for Sedentary Patients
Women who are currently sedentary can be encouraged to start an exercise program during pregnancy. Many women prefer to start exercising during the second trimester, after the nausea, vomiting, and fatigue of the first trimester have subsided and before the physical limitations of the third trimester begin.58 As is the case for any sedentary person starting an exercise program, pregnant women should be instructed to begin exercise at low intensity and gradually increase time and intensity to avoid overuse injuries. Starting with 15 minutes of continuous activity 3 days per week and gradually increasing to 30 minutes 4 days per week is recommended.58
Some previously inactive women may find swimming or pool-based aerobic exercise easiest to do, but walking, yoga for pregnancy, stationary biking, and other low-impact aerobic machines may also be well tolerated. Providing pregnant women with a variety of exercise options may help prevent boredom with the exercise routine and reduce the risk of overuse injury. Of course, with any exercise routine, a good warm-up and cooldown period are recommended.
Guidelines for Active Patients
Women who are currently active can often continue their regular exercise regimen. During later stages of pregnancy, physical comfort levels should dictate types and level of activity. Women who are currently active, especially at high levels, should be counseled to expect a gradual decline in performance throughout pregnancy, which may start as early as the first trimester. Only a few small studies have followed very active women exercising at high intensities during pregnancy (1 to 2.5 hours, 5 to 6 days per week), and, thus far, no maternal or fetal complications have been identified, though birth weight may be lower in these infants.1,28,30,57,60
Some have expressed concern that the weight gain and ligamentous laxity associated with pregnancy may predispose active women to musculoskeletal injury during pregnancy. However, studies have failed to demonstrate increased musculoskeletal injury rates in physically active pregnant women, partly because of decreased participation in contact, pivoting, and jumping activities later in pregnancy when ligamentous laxity is greatest.7,28,29
Guidelines for Competitive Athletes
Athletes who were used to high exercise levels before pregnancy may need to reduce or forgo some activities during pregnancy. The goal should be to maintain basic fitness levels without trying to reach peak fitness or train for athletic competition.58 Some situations faced by pregnant athletes may need special consideration.
Contact sports with high risk for abdominal trauma and activities with high risk for falling should be avoided, especially after the first trimester, to reduce injury risk to the fetus.1,58
Exercise at high altitude may present risks, such as preterm labor and bleeding, especially at altitudes above 6,000 ft (1,830 m) and in women who have medical or obstetric complications that impair oxygen delivery.61 A few small studies have failed to document abnormal maternal or fetal responses to short-term, submaximal exercise at an altitude of about 6,000 ft.62,63 It is also reassuring that pregnant women who experience exposure to high altitudes during vacation time in ski resorts or during work as flight attendants do not seem to experience adverse effects.64 Thus, moderate exercise at altitudes up to 6,000 ft appears to be safe as long as the patient has no other complications.
Strenuous exercise before acclimatization may increase the risk of pregnancy complications.61 Anyone exercising at altitude, including the pregnant athlete, should be able to recognize early symptoms of altitude sickness, such as headache, excessive fatigue, difficulty breathing, or lack of appetite, and be prepared to descend to lower altitudes if symptoms persist or worsen. Advanced symptoms, including severe shortness of breath, coughing up pink mucus, or confusion, necessitate immediate return to lower altitude and medical evaluation to avoid serious complications. All athletes who do not live at altitude and wish to visit sites at higher elevations should be encouraged to ascend gradually to enhance acclimatization and help prevent altitude sickness.
Scuba diving should also be discouraged in pregnant women, because the fetus is unprotected from decompression injury and may be at risk for malformation and gas embolism.65
Best Possible Outcome
Physicians who see pregnant patients should be able to discuss exercise recommendations based on each woman's prepregnancy activity level, general health, and fitness goals. Unless contraindications are a factor, moderate aerobic and strength-conditioning exercises should be encouraged to help prevent or lessen excessive weight gain, loss of physical conditioning, musculoskeletal discomfort, pregnancy-induced hypertension, gestational diabetes, and other conditions related to pregnancy.
Dr Kelly is a family physician at Case Western Reserve University and Rainbow Babies and Children's Hospital in Cincinnati. Address correspondence to Amanda K. Weiss Kelly, MD, 2460 Edgerton Rd, University Heights, OH 44118; e-mail to [email protected].
Disclosure information: Dr Kelly discloses no significant relationship with any manufacturer of any commercial product mentioned in this article. No drug is mentioned in this article for an unlabeled use.