Exercise During Pregnancy and Postpartum Period
WHEC Practice Bulletin and Clinical Management Guidelines for healthcare providers. Educational grant provided by Women's Health and Education Center (WHEC).
The current Centers for Disease Control and Prevention (CDC) and American College of Sports Medicine (ACSM) recommendation for exercise, aimed at improving the health and well-being of non-pregnant individuals, suggests that an accumulation of 30 minutes or more of moderate exercise a day should occur on most, if not all, days of the week (1). In the absence of either medical or obstetric complications, pregnant women also can adopt this recommendation. The physiologic and morphologic changes of pregnancy may interfere with the ability to engage safely in some forms of physical activity. A woman’s overall health, including obstetric and medical risks, should be evaluated before prescribing an exercise program. Generally, participation in a wide range of recreational activities appears to be safe during pregnancy; however, each sport should be reviewed individually for its potential risk, and activities with a high risk of falling or those with a high risk of abdominal trauma should be avoided during pregnancy. Scuba diving also should be avoided throughout pregnancy because the fetus is at an increased risk for decompression sickness during this activity. In the absence of either medical or obstetric complications, 30 minutes or more of moderate exercise a day on most, if not all, days of the week is recommended for pregnant women.
The purpose of this document is to review existing guidelines for exercise during pregnancy and the postpartum period. Several versions of exercise guidelines for pregnancy have been published. Women of childbearing age are at increased risk of gestational diabetes mellitus (GDM), which has been linked strongly to obesity. Weight gain during pregnancy can be excessive, and some women tend to retain that weight after delivery. Gaining excessive weight during pregnancy can result in obesity-associated comorbidities, which are a major health concern in the United States. This review aims to address gaps in existing data by evaluating fetal well-being in response to exercise using standard tests obstetricians find relevant in determining the health of a fetus.
Epidemiologic data suggest that exercise may be beneficial in the primary prevention of gestational diabetes, particularly in morbidly obese women (Body Mass Index - BMI > 33) (2). The American Diabetes Association has endorsed exercise as “a helpful adjunctive therapy” for gestational diabetes mellitus when euglycemia is not achieved by diet alone (3). Specific evidence-based recommendations on exercise during pregnancy are lacking. The majority of pregnant women seek exercise information from commercial books, magazines, and friends rather than their healthcare providers. Obstetricians are hesitant to advise sedentary women to initiate exercise during pregnancy, and nearly half counsel exercisers to reduce activity (4). Many obstetricians continue to recommend limiting maternal heart rate to less than 140 beat per minute (bpm), a restriction removed from the American College of Obstetricians and Gynecologists (ACOG) guidelines in 1994. Existing recommendations for physical activity during pregnancy have been extrapolated from the physical activity and public health literature. The first public health guidelines were subsequently adopted by ACOG (5). Updated public health recommendations provide specific definitions of moderate and vigorous intensity. In 2008, the U.S. Department of Health and Human Services issued comprehensive guidelines on physical activity and pregnant women are addressed (3). First, healthy women (non-exercisers and moderate exercisers) should begin or continue moderate-intensity aerobic activity during pregnancy, accumulating at least 150 minutes per week. Because vigorous-intensity exercise has not been carefully studied, these women are not advised to start vigorous exercise. Second, women who currently exercise vigorously may continue their exercise provided they remain healthy.
Despite recommendations for pregnant women to be active the majority is not meeting guidelines and physical activity consistently decreases during pregnancy (6). We encourage that obstetricians should encourage exercise during pregnancy in part as a result of a paucity of data on fetal safety. This lack of counseling may deprive women of overall health benefits of exercise and pregnancy-specific benefits such as a decreased risk of GDM. The cardiovascular changes associated with pregnancy are an important consideration for pregnant women both at rest and during exercise. After the first trimester, the supine position results in relative obstruction of venous return, and therefore, decreased cardiac output and orthostatic hypotension. For this reason, pregnant women should avoid supine position, during exercise as much as possible. Motionless standing also is associated with a significant decrease in cardiac output so this position should be avoided (7).
Epidemiologic studies have long suggested that a link exists between strenuous physical activities, deficient diets, and the development of intrauterine growth restriction (IUGR). This is particularly true of pregnant women engaged in physical work. It has been reported that pregnant women whose occupations require standing or repetitive, strenuous, physical work (e.g. lifting) have a tendency to deliver earlier and have small-for-gestational-age infants. However, other reports have failed to confirm these associations suggesting that several factors or conditions have to be present for strenuous activities to affect fetal growth or outcome (8). In general, participation in a wide range of recreational activities appears to be safe. The safety of each sport is determined largely by the specific movements required by that sport. Participation in recreational sports with a high potential for contact, such as ice hockey, soccer, and basketball, could result in trauma to both the woman and fetus. Similarly, recreational activities with an increased risk of falling, such as gymnastics, horseback riding, downhill skiing, and vigorous racquet sports, have an inherently high risk for trauma in pregnant and non-pregnant women. Those activities with a high risk of falling or for abdominal trauma should be avoided during pregnancy (9). Scuba diving should be avoided throughout pregnancy because during this activity the fetus is at increased risk for decompression sickness secondary to filter bubble formation (10), (11).
Exertion at altitudes of up to 6,000 feet appears to be safe; however, engaging in physical activities at higher altitude carries various risks (7), (11). All women who are recreationally active should be made aware of signs of altitude sickness for which they should stop the exercise, descend from the altitude, and seek medical attention. Data regarding the effects of exercise on core temperature during pregnancy are limited. There have been no reports that hyperthermia associated with exercise is teratogenic (7). Competitive athletes are likely to encounter the same physiologic limitations during pregnancy faced by recreational athletes during pregnancy. The competitors tend to maintain a more strenuous training schedule throughout pregnancy and resume high intensity postpartum training sooner. The concerns of the pregnant, competitive athlete fall into two general categories: 1) the effects of pregnancy on competitive ability, and 2) the effects of strenuous training and competition on pregnancy and the fetus (12). Such athletes may require close obstetric supervision.
In the Health and Human Services Advisory Committee report (10), it is noted that approximately 600 studies were published between 1985 and 1994 indicating exercise during pregnancy causes “no harm”, and many studies have reported no negative effects on several pregnancy outcomes, including rate of preterm delivery, birth weight, and mode of delivery (9), (13). However, fewer data are available on fetal responses to exercise and this study provides evidence that acute fetal well-being is not negatively affected when exercising according to recommendations (14). In the recent Health and Human Services recommendations for the general population, various methods of gauging exercise intensity are provided in addition to target heart rates. Perceived exertion scales are one suggested method. Rating of perceived exertion scales has been validated as a clear, concise, and effective means to regulate exercise intensity in a number of populations (15). Two scales are generally used, the original 6-20 scale and the category rating of perceived exertion scale, ranging from 0 to10, with numbers anchored by verbal expressions that are simple and understandable. According to the Health and Human Services guidelines, a 5-6 on the category rating of perceived exertion scale reflects moderate intensity and a 7-8 reflects vigorous intensity. However, this may not be appropriate for pregnant women. Walking is one of the easiest and most accessible forms of exercise; therefore, is recommended to all healthy pregnant women. Healthy women should get at least two and one half hours of moderate-intensity aerobic activity a week during pregnancy and the time after delivery, preferably spread through the week. Pregnant women who habitually engage in vigorous aerobic activity or who are highly active can continue during pregnancy and the time after delivery, provided they remain healthy and discuss with their health care provider how and when activity should be adjusted over time.
Absolute Contraindications to Aerobic Exercise during Pregnancy
These are absolute contraindications to aerobic exercise during pregnancy (7):
Relative Contraindications to Aerobic Exercise during Pregnancy
Warning Signs to Terminate Exercise while Pregnant
Fewer studies have considered maternal mood during pregnancy, yet available evidence suggests that maternal physical activity improves mood and is associated with increased self-esteem (9). Conflicting results exist relating maternal physical activity to the course of labor and delivery. Some studies report easier and shorter deliveries, others find no effect, and some show that induction of labor is used more often among women who exercise (18). Variances in methodology and activity definitions make these studies difficult to summarize and compare. A recent study (18) showed that women who exercised during pregnancy were less likely to have preterm delivery compared to their sedentary counterparts. However, the authors were not able to clearly separate the role of moderate versus vigorous activity on this effect.
If you're pregnant and looking for ways to relax or stay fit, you may be considering prenatal yoga. Good for you! But did you know that prenatal yoga may also help you prepare for labor and promote your baby's health? Before you start prenatal yoga, understand the range of possible benefits, as well as what a typical class entails and important safety tips. There are many different styles of yoga – some more strenuous than others. Prenatal yoga or hatha (gentle) yoga is the best choices for pregnant women. If they are not an option, talk to the instructor about your pregnancy before starting any other yoga class. Be careful to avoid Bikram yoga, commonly called hot yoga, which involves doing vigorous poses in a room heated to 100 to 110 F (38 to 43 C). Bikram yoga may raise your body temperature too much, causing a condition known as hyperthermia. In addition, ashtanga and other types of power yoga may be too strenuous for women who aren't experienced yoga practitioners.
A typical prenatal yoga class may involve (16):
Strength Training, Exercise Intensity during Pregnancy
Increasing the amount of vigorous-intensity exercise is an important goal for pregnant women, especially those who are overweight or obese. Non-oxidative type IIb muscle fibers (which burn minimal fat) are increased in obese women (body mass index - BMI, calculated as weight (kg)/ [height (m)]2] 30 or higher) and are related directly to BMI. The greater the BMI, the more type IIb muscle fibers a woman possesses. In addition, the greater the BMI, the lower the percentage of type I oxidative fibers (fat burning). Weight loss alone, or weight loss with physical activity, can improve muscle oxidative capacity in obese women with and without diabetes. The physical activity-induced increase in muscle oxidative capacity increases the capacity to burn fat throughout the day, which would limit weight gain. In overweight and obese women, vigorous-intensity exercise, which increases the energy expenditure post-exercise compared with low-intensity exercise, should limit weight gain (21). To adhere to the exercise prescription, pregnant women should follow the rating of perceived exertion. The rating of perceived exertion is subjective and ranks overall effort of exertion and fatigue from 6 (no exertion) to 20 (maximal exertion). A rating of 6 = no exertion at all, 7-8 = extremely light, 9-10 = very light, 11-12 = light, 13-14 = somewhat hard, 15-16 = hard, 17-18 = very hard, 19 = extremely hard, 20 = maximal exertion. This scale scores the total exertion, overall exertion, and fatigue level of an exercise. The more exertion, the less total exercise time is required to reach the recommended weekly physical-activity expenditure goal. The rating of perceived exertion for proposed light and vigorous physical activity options in pregnant women is around 12-14 and 15-16, respectively.
Increasing weekly physical-activity energy expenditure is an important goal for pregnant women. A recent meta-analysis has shown that higher levels of physical activity in early pregnancy are associated with a 24% lower risk of developing GDM (22). Those women who had the highest levels of physical activity before pregnancy had approximately a 55% lower risk of developing GDM compared with women with the lowest levels physical activity (22). Specifically, there is a relationship between energy expenditure in metabolic equivalent task-h/wk and GDM risk. The vigorous physical activity option reduces the total exercise time by about 60% compared with the light physical activity option. Light strength training does not negatively affect the newborn’s body size and overall health.
Safety guidelines during pregnancy muscle strengthening (23): For pregnant adults aged 18-45 years of age, 8 to 10 muscular strength exercises can be performed for one to two sessions per week on non-consecutive days. One aerobic training session can be replaced by a muscle strengthening session in the weight room or at home. Use lighter weights and more repetitions – heavy weights may overload joints already loosened by increased levels of the hormone relaxin during pregnancy. For example, if one usually performs leg presses with 35 lb for 8 to 12 repetitions, try 20 lb for 15 to 20 repetitions or, if one typically performs a chest press with 15 lb for 8 to 12 repetitions, try 8 lb for 15-20 repetitions. Try to avoid walking lunges. These may raise the risk of injury to connective tissue in the pelvic area. Be careful with free weights because they may involve the risk of hitting the abdomen. Women can use resistance bands instead, which offer different amounts of resistance and varied ways to do weight during training and should pose minimal risk to the abdomen.
Try not to lift while flat on you back. In the second and third trimesters, lying on your back may cause the uterus to compress a major vein, the inferior vena cava, into which blood from the pregnant uterus flows. This increased pressure can be transmitted to the placenta and could compromise fetal blood flow in the gas-exchange area, thereby limiting oxygen supply to the fetus. An easy modification is to tilt the bench to an incline. Try to avoid the valsalva maneuver. This maneuver, forcefully exhaling without actually releasing air, can result in a rapid increase in blood pressure and intra-abdominal pressure and may decrease oxygen flow to the fetus. Also, on rare occasions, the uterus can be displaced against the inferior vena cava, which can result in a decrease in blood pressure. Thus, a decrease in blood pressure also can occur with the valsalva maneuver during pregnancy, but this is uncommon.
Listen to your body. The most important rule is to pay attention to what is going on physically. If you feel muscle strain or excessive fatigue, modify the moves and reduce the frequency of the workouts. Pregnancy is not the time to perform heavy weightlifting, but muscle strengthening according to these guidelines will burn calories and increase the resting metabolic rate.
Many of physiologic and morphologic changes of pregnancy persist 4-6 weeks postpartum. Thus, pre-pregnancy exercise routines may be resumed gradually as soon as it is physically and medically safe. This will vary from one individual to another with some women able to resume an exercise routine within days of delivery. There are no published studies to indicate that, in the absence of medical complications, rapid resumption of activity will result in adverse effects. Having undergone detraining, resumption of activities should be gradual. No known maternal complications are associated with resumption of training. Moderate weight reduction while nursing is safe and it does not compromise neonatal weight gain (17). Finally, a return to physical activity after pregnancy has been associated with decreased incidence of postpartum depression, but only if the exercise is stress relieving and not stress provoking.
Available evidence has shown maternal physical activity during the postpartum period is associated with enhanced mood, increased cardiovascular fitness, and obesity prevention. Larson-Meyer reviewed (18) approximately 60 cross-sectional studies and registered clinical trials on postpartum weight reduction, specifically, looking at postpartum exercise. When compared to no physical activity, moderate physical activity did not appear to increase postpartum weight reduction unless caloric restriction was included. Studies also have showed that moderate intensity aerobic exercise did not adversely affect milk volume, composition, or infant growth. Some longitudinal data on future disease risk come from Rooney and colleagues (19) who examined nearly 800 women immediately postpartum and again 15 years later. Disease and risk factor development (diabetes, heart disease, dyslipidemia, and hypertension) were directly related to weight gain over 15 years (20). Women who continued to perform aerobic exercise postpartum were less likely to become obese than those who did not. In summary, in the absence of medical complications, physical activity during the postpartum period is beneficial to the overall health of the mother (both in the short- and long-term) while not adversely affecting her newborn’s development.
Recreational and competitive athletes with uncomplicated pregnancies can remain active during pregnancy and should modify their usual exercise routines as medically indicated. The information on strenuous exercise is scarce; however, women who engage in such activities require close medical supervision. Previously inactive women and those with medical or obstetric complications should be evaluated before recommendations for physical activity during pregnancy are made. Exercise during pregnancy may provide additional health benefits to women with gestational diabetes. A physically active woman with a history of or risk for preterm labor or fetal growth should be advised to reduce her activity in the second and third trimesters. In conclusion, healthcare providers should feel more reassured that pregnant women can exercise during pregnancy when following existing exercise recommendations. The potential public health benefits of exercise are too great for obstetricians to miss the opportunity to effectively counsel pregnant women about this important health-enhancing behavior.