INTRODUCTION — Although regular physical activity is one of the most important actions people can take to improve their health, nearly 80 percent of adults are not meeting guidelines for both aerobic and muscle-strengthening activity, and only 50 percent meet guidelines for aerobic physical activity. Women who are pregnant or postpartum also benefit from regular physical activity [1-5], but a population-based survey in the United States determined that 60 percent of pregnant women do not engage in either moderate or vigorous leisure physical activity [6].

Data from leading obstetric organizations and numerous systematic reviews demonstrate that exercise in pregnancy is safe and can improve multiple pregnancy outcomes (eg, reduced frequency of excessive gestational weight gain, gestational diabetes, postpartum weight retention) [7,8]. Pregnancy provides a unique opportunity for behavior modification counseling since pregnant women are highly motivated toward healthy behaviors and are under close medical supervision by a health care provider. Health care providers should carefully evaluate pregnant women for obstetric or medical complications before making recommendations on physical activity and participation [9]. Even in uncomplicated pregnancies, exercise routines may have to be modified during pregnancy to accommodate the normal anatomic and physiologic changes that occur in pregnant women and to avoid adverse effects on the fetus. The greatest barriers to exercise in pregnancy are nausea/fatigue and lack of time; focusing education and interventions on these barriers may help pregnant women achieve recommended exercise levels [10].

This topic will discuss the benefits and risks of exercise during pregnancy and provide guidance about the frequency, type, intensity, and duration of exercise for various populations of pregnant and postpartum women.

BENEFITS AND RISKS

Benefits — Potential benefits of exercise in pregnancy include:

●The same long-term medical and psychological benefits of exercise derived by nonpregnant individuals. (See "The benefits and risks of aerobic exercise", section on 'Benefits of exercise'.)

●Maintenance or improvement of cardiorespiratory endurance, muscular strength and endurance, flexibility, and body composition [11-15].

●Maintenance or improvement in agility, coordination, balance, power, reaction time, and speed [11-14].

●Avoidance of excessive gestational weight gain and its consequences [16-20]. Improvement in cardiometabolic health [21].

●Reduction in severity of pregnancy-related musculoskeletal discomforts, such as low back, lumbopelvic, and pelvic girdle pain [22].

●Prevention or reduction of urinary incontinence – Pelvic floor muscle exercises (Kegel exercises) performed during pregnancy help to decrease the short-term risk of urinary incontinence in women without prior incontinence, but a long-term benefit has not been established. (See "Effect of pregnancy and childbirth on urinary incontinence and pelvic organ prolapse", section on 'Prophylactic pelvic floor muscle exercises'.)

●Reduction in risk of delivering a macrosomic or large for gestational age newborn (odds ratio [OR] 0.69, 95% CI 0.55-0.86 in one meta-analysis of randomized trials [23]). A reduction in neonatal adipose tissue has also been observed at one month of age [24].

●Reduction in assisted vaginal delivery, but no effect on prelabor rupture of membranes, cesarean delivery, induction of labor, length of labor, vaginal tears, fatigue, injury, musculoskeletal trauma, and diastasis recti [25].

●Probable reduction in risk of developing gestational diabetes (relative risk [RR] 0.45 to 1.1 in 14 meta-analyses [18]). (See 'Women with or at risk for diabetes' below.)

●Possible reduction in risk of developing preeclampsia [20,26]. In a meta-analysis of 11 cohort and 4 case-control studies, the risk of preeclampsia appeared to be reduced with increasing levels of physical activity before and during early pregnancy [26]. For example, for high versus low physical activity in early pregnancy, the summary RR was 0.79 (95% CI 0.70-0.91).

These benefits are not completely independent. For example, overweight and obese women who lose significant weight prepregnancy through exercise and diet and avoid excessive gestational weight gain can reduce their likelihood of developing gestational diabetes and diabetes- and obesity-related comorbidities, such as macrosomia, preeclampsia, obstetrically indicated preterm delivery, and cesarean delivery. (See "Obesity in pregnancy: Complications and maternal management" and "Gestational diabetes mellitus: Obstetric issues and management", section on 'Consequences of GDM'.)

Risks — Potential risks of exercise in pregnancy include:

●Maternal trauma, which may lead to an obstetric complication, such as abruption, and thus impact the fetus.

●Hyperthermia – Maternal core temperature of 102.2°F (39°C) in the first four to six weeks of pregnancy has been associated with an increased risk for neural tube defects [27,28]. It is unlikely that body core temperature would reach teratogenic levels during normal exercise, but a prudent approach is warranted. In one study, when pregnant women biked on an ergometer for 60 minutes at 50 percent of VO₂max, their body core temperature increased by <1°C [29].

Aquatic exercise appears to provide better conductivity/control in both cool and warm water, as long as the intensity and the duration of exercise are controlled. In a systematic review of studies of core temperature response of pregnant women to exercise or passive heat stress across gestation, the highest mean end-trial core temperature was 38.3°C (95% CI 37.7-38.9°C) for land-based exercise, 37.5°C (95% CI 37.3-37.7°C) for water immersion exercise, 36.9°C (95% CI 36.8-37.0°C) for hot water bathing, and 37.6°C (95% CI 37.5-37.7°C) for sauna exposure [30]. The authors concluded that pregnant women could safely engage in: (1) exercise for up to 35 minutes at 80 to 90 percent of their maximum heart rate at 77°F/25°C and 45 percent relative humidity (RH); (2) water immersion (≤92°F/33.4°C) exercise for up to 45 minutes; and (3) sitting in hot baths (104°F/40°C) or hot/dry saunas (158°F/70°C; 15 percent RH) for up to 20 minutes, irrespective of pregnancy stage, without reaching a core temperature exceeding the teratogenic threshold. However, prolonged land or aquatic exercise should be avoided in extremely cold or warm environments.

In another systematic review of studies of the effects of prenatal exercise on pregnancy outcome, exercise was not associated with an increased risk for congenital anomalies [31].

Of note, thermoregulation improves during pregnancy, possibly due to increased circulation to the skin, increased minute ventilation, and increased plasma volume [2].

●Reduction in uteroplacental blood flow – During exercise, the body of evidence shows that blood flow is preferentially directed to working muscles [32,33]. Reports of sporadic episodes of fetal bradycardia during maternal exercise have raised concerns that maternal exercise could compromise uterine blood flow, resulting in hypoxia-related fetal injury [34-36]. However, the body of evidence suggests that the normal fetus compensates for any transient changes in uteroplacental blood flow during maternal exercise and is not at risk of harm (including death), even in previously sedentary pregnant women [37].

External fetal monitors have been used extensively to evaluate fetal heart rate (FHR) responses to maternal exercise on a treadmill or exercise cycle, and the findings have been reassuring. In these studies, maternal exercise was generally associated with a 2 to 10 beat/minute increase in FHR, generally independent of gestational age and intensity of exercise [34]. The increase in FHR was sometimes accompanied by FHR accelerations, and post-exercise FHR reactivity was generally achieved within 20 minutes. It is likely that the increase in FHR is a normal physiologic response to a transient reduction in uterine blood flow and to transplacental passage of maternal catecholamines, which are elevated during exercise. These fetal responses are protective mechanisms that increase blood flow and facilitate exchange of the respiratory gases across the placenta.

Although a prolonged reduction in uteroplacental blood flow can result in fetal hypoxemia, leading to vagal stimulation and bradycardia in some cases [38], the body of evidence suggests that the incidence of bradycardia during and following acute exercise is not elevated compared with rest [39].

Studies of the fetal responses to maternal exercise are limited by the technical difficulty of externally recording the FHR during exercise. FHR tracings are frequently obscured by artifacts induced by maternal or fetal movement. To avoid this problem, a pilot study applied internal scalp electrodes to the fetuses of two elite athletes who volunteered to exercise while in labor [40]. The athletes engaged in an incremental resistance bicycle ergometry test and reached 60 percent of their last known maximum aerobic capacity, after which the tests were suspended. In each case, the FHR remained normal during the test. Although the study was small, it provides additional evidence that maternal exercise at this level is not deleterious to the fetus, even during the most challenging exercise conditions, such as labor. By contrast, fetal bradycardia was observed in two of six Olympic-level athletes at 23 to 29 weeks of gestation who exercised at ≥90 percent of maximal heart rate and whose mean uterine artery blood flow fell >50 percent from baseline [41]. FHR and umbilical artery Doppler indices normalized within 10 minutes of maternal recovery after cessation of exercise. As there are no proven health benefits for strenuous exercise in pregnancy, it should only be considered by elite athletes whose pregnancies are closely monitored. (See 'Intensity of exercise' below.)

A few studies have evaluated parameters other than the FHR, such as standard umbilical and uterine artery Doppler indices [39] and fetal breathing and activity patterns [42,43], to assess fetal health in response to maternal aerobic dancing, cycling, or walking/jogging on a treadmill. Umbilical and uterine artery Doppler blood flow did not change during exercise, but transient changes were noted in some women immediately post exercise [36,44-46]. These studies also suggest that fetal responses to maternal exercise are transient, normal physiologic responses, and adverse fetal events are unlikely to occur in otherwise uncomplicated gestations.

Data on longer term outcomes (school-age children) are limited, but the body of evidence suggests that regular moderate intensity exercise during pregnancy has no adverse effect on neurodevelopment [47].

●Impaired fetal growth – Although exercise may have a small negative effect on birth weight, it does not appear to increase the risk of delivery of a small for gestational age infant. In a 2015 systematic review of the effect of supervised prenatal exercise on fetal growth, randomization to standard prenatal care plus a supervised prenatal exercise program (aerobic, resistance, or both) did not adversely affect birth weight compared with standard prenatal care alone (mean difference in birth weight -31 g) or the risk for delivery of a small for gestational age newborn (OR 1.02, 95% CI 0.72-1.46) [23]. The frequency of the prescribed exercise regimen ranged from one to five times per week, the time of each session ranged from 15 to 70 minutes, and the duration of the interventions ranged from 6 to 33 weeks, ending in the mid to late third trimester. Other meta-analyses have reported no or small (<60 grams) differences in birth weight [48]. Reviews of these studies revealed numerous potential biases and methodological issues: other confounding conditions or complications; small sample size; the trimester in which exercise is performed; the type (weight-bearing versus non-weight-bearing), intensity, and duration of exercise; eating habits; and active or sedentary control groups [14,49]. Although reassuring, these findings do not address the safety of more intense, frequent, and prolonged exercise sessions in pregnancy. Information on this type of exercise in pregnancy is sparse [14,48,49]. (See 'Elite/competitive athletes' below.)

Other — Light to moderate recreational physical activity/exercise most likely does not increase the risk of miscarriage or preterm delivery in women with uncomplicated pregnancies; recall bias in positive retrospective studies is a limitation of these studies [37].

Similarly, a meta-analysis investigating the effects of vigorous intensity exercise performed throughout pregnancy (10 cohort studies with >32,000 participants and 5 randomized trials with 623 participants) found that vigorous-intensity exercise across gestation, including the third trimester, appeared to be safe for most healthy pregnant women (eg, no significant increase in risk for small for gestational age or low birth weight infants) [50]. However, further research is needed on the effects of vigorous intensity exercise in the first and second trimester and of exercise intensity exceeding 90 percent of maximum heart rate.

PRESCRIBING EXERCISE FOR PREGNANT WOMEN — The following table summarizes the author's recommendations and precautions for exercise during pregnancy (table 1). The recommendations and precautions are discussed in detail below.

For the previously sedentary woman, pregnancy provides a unique opportunity for adopting a more healthy lifestyle that includes both physical activity and healthy eating. Health care providers could use the American College of Obstetricians and Gynecologists (ACOG) behavior modification techniques (the 5A's: assess, advise, agree, assist, and arrange) to facilitate behavioral change [51].

Pre-exercise and ongoing risk assessment — Pregnant women who want to continue or initiate an exercise program should be evaluated for medical and obstetric factors that may increase their risk for maternal or fetal complications and injuries. As with nonpregnant individuals, a thorough clinical evaluation should be performed, including medical history, current medical condition and medications, past and present pregnancy-related complications, and current exercise and physical activity levels. For each exercise/physical activity, the following should be noted:

●Intensity (light, moderate, vigorous)

●Frequency (per week)

●Duration (minutes per session)

Also note any changes in exercise/physical activity from prepregnancy levels.

Standardized questionnaires and resources are available to assist with the screening process, such as the Physical Activity Readiness Medical Examination (PARmed-X) for Pregnancy developed by the Canadian Society for Exercise Physiology [52], Physical Activity Readiness form [53], the American College of Sports Medicine's Health/Fitness Standards and Guidelines assessment manual [54], and the rapid assessment of physical activity intake form developed by the Canadian Exercise in Pregnancy Committee [4].

Contraindications to exercise during pregnancy — Most pregnant patients can be advised to exercise; however, those with some preexisting or developing medical conditions may have to restrict or avoid exercise. The author uses the guideline published by ACOG in 2015 (table 2) [55], which the International Olympic Committee expert group adopted in its guideline [48]. However, some have called for reevaluation of the disorders that have been considered absolute and relative contraindications to prenatal exercise since there is no high-quality evidence demonstrating an adverse effect of moderate to vigorous physical activity in some of these settings (eg, twin pregnancy, gestational hypertension, anemia) [56]. (See "Exercise for adults: Terminology, patient assessment, and medical clearance", section on 'Medical assessment and clearance for exercise'.)

Exercise can be adversely impacted by some obstetric complications, independent of the woman's previous fitness level. For example, Doppler velocimetry of pregnancies complicated by preeclampsia and fetal growth restriction has revealed increased uteroplacental resistance indices and fetal cerebral vasodilation after exercise [57,58], which supports avoidance of moderate or strenuous exercise in pregnancies with uteroplacental insufficiency. Exercise avoidance is not useful for preventing the development of uteroplacental insufficiency.

Exercise prescription — Exercise prescription in pregnancy follows the same principles and guidelines and the same components as prescribed for nonpregnant individuals, modified to minimize maternal and fetal risks/injuries and maximize benefits [3,53].

The exercise prescription includes a description of:

●Types of exercise to include/avoid

●Intensity, progression, and difficulty over time

●Frequency and duration

A typical exercise session begins with warm-ups and stretching (5 to 10 minutes), followed by the exercise program (30 minutes per session and at least 150 minutes/week), and ending with cool down (5 to 10 minutes).

Choosing an exercise program — The exercise prescription for the development and maintenance of fitness consists of activities to improve cardiorespiratory (aerobic exercise) and musculoskeletal (resistive exercise) fitness. Women should choose exercises that activate large muscle groups in a rhythmic and continuous fashion (eg, walking, aerobic dance, swimming, cycling, rowing, jogging) and that maintain strength (eg, weights, elastic bands), core muscles, and flexibility (table 3).

Women may safely continue most of their prepregnancy recreational exercise activities or modify them as pregnancy conditions change. Women who engaged in regular exercise before pregnancy and who have uncomplicated pregnancies should be able to engage in high-intensity exercise, such as jogging and aerobics, during pregnancy.

However, some activities should be avoided (table 3). The following principles should be considered when choosing an exercise program in pregnancy:

●Activities with a high risk of falling or those with a high risk of abdominal trauma (full contact sports) are contraindicated because of the risk for placental abruption, as well as maternal injury.

●Activities that require jumping movements and quick changes in direction can stress joints and increase the risk of joint injury. Flexibility exercises should be individualized to reduce susceptibility to joint injury.

Hormonal changes in pregnancy may cause ligament laxity; thus, joints are supported less effectively, especially in women with poor muscle mass. Activities that may result in excessive joint stress should be discontinued, modified, or include cautionary advice, with consideration of individual abilities.

●Yoga is generally safe for pregnant women and their fetuses [59,60]. It can increase maternal strength and fitness as well as reduce stress. Women should avoid hot yoga and use their judgment about modifying or avoiding yoga positions that are uncomfortable or likely to result in loss of balance and falling.

●Exercises typically performed in a supine position should be avoided after the first trimester because aortocaval compression in this position predisposes approximately 10 percent of pregnant women to hypotensive episodes, especially in the third trimester. The supine position can also compromise uterine blood flow through compression of the aorta. However, these effects appear to be more of a problem during supine rest than supine exercise [61], and adverse pregnancy effects from supine exercise have not been proven [62].

Some of these exercises may be performed in other positions, such as tilting the torso to 45 degrees, lying on the side, sitting, or standing.

●Strength training can be performed during pregnancy, but information about safety is limited. Studies focused on low-intensity resistance training with low weights (free or machine, ≤10 pounds [4.5 kg]) with multiple repetitions lifted through a dynamic range of motion suggest this level of activity is safe and effective during pregnancy [63,64]. Although supporting data are lacking, a prudent approach is to avoid heavy-resistance weight lifting, any exercises that result in marked straining (especially training to failure), and intense repetitive isometric exercises during pregnancy. Women who continue heavy strength training in pregnancy should be aware that the Valsalva maneuver causes a rapid increase in blood pressure and intraabdominal pressure and therefore may temporarily decrease uteroplacental blood flow [2]. Avoiding this maneuver by exhaling with an open airway seems prudent. Contracting the pelvic floor muscles before and during heavy lifting can counteract the impact of increased intraabdominal pressure on the pelvic floor [48]. Pelvic floor muscle training during pregnancy can reduce the risk of urinary incontinence. (See "Effect of pregnancy and childbirth on urinary incontinence and pelvic organ prolapse", section on 'Prophylactic pelvic floor muscle exercises'.)

In the United States, the National Institute for Occupational Safety and Health has published clinical guidelines for occupational lifting in uncomplicated pregnancies [65]. In the absence of better information, these guidelines may be extrapolated to nonoccupational recreational weight lifting and are reviewed separately. (See "Working during pregnancy", section on 'Lifting'.)

●Exercise can be weight-bearing or non-weight-bearing, with different impacts on the body [49,66]. Weight-bearing exercises are performed less efficiently in pregnancy and are more energy-costly, since they contain a component of added body weight [67], but are well tolerated by previously active pregnant women.

Because of pregnancy-related anatomical and physiological changes, women may prefer non-weight-bearing physical activities during pregnancy (see "Maternal adaptations to pregnancy: Musculoskeletal changes and pain", section on 'Normal pregnancy changes'). Aquatic exercise is a particularly advantageous non-weight-bearing activity for pregnant women since the following occur during immersion: Peripheral edema is reduced, the forces across weight-bearing joints are reduced, body heat is readily dissipated into the water, and loss of balance and falling are of minimal concern [68]. Swimming in the prone position has not been associated with adverse effects and has the advantage of creating a weight-supported condition that is easily tolerated.

●Prolonged or intense exercise can lead to dehydration and hyperthermia, which should be avoided. Basal metabolic rate and heat production are increased during pregnancy so maintenance of euhydration is particularly critical to heat balance during any prolonged exercise and any exercise in hot, humid weather. (See 'Hydration and energy' below and "Exertional heat illness in adolescents and adults: Epidemiology, thermoregulation, risk factors, and diagnosis" and "Exertional heat illness in adolescents and adults: Management and prevention".)

To prevent hyperthermia, the Royal College of Obstetricians and Gynaecologists recommends limiting exposure to environmental temperatures exceeding 90°F (32°C) and keeping hydrotherapy pool temperatures ≤95°F (35°C) [69].

●Scuba diving should be avoided throughout pregnancy because the fetus is at increased risk for decompression sickness secondary to the inability of the fetal pulmonary circulation to filter bubble formation [3,70].

●Lowlanders should avoid exercise during the first three to four days of exposure to moderate to high altitude (above 6000 feet [2500 m]) because of the reduction in oxygen availability [71]. PO₂ values at 5000 and 8000 feet are 135.0 and 118.3 mmHg, respectively. Adverse effects on the fetus have not been observed in studies conducted at altitudes of up to 6000 feet (2500 m) that are typically used for mountain sports, such as hiking or skiing [71,72]. One study demonstrated that rapid ascent to 6000 feet is safe both for mother and fetus and that brief bouts of mild-moderate exertion is tolerated, but limitations occur at maximal aerobic capacity exertion [71].

Maladaptation at altitude could result in acute mountain sickness, a medical emergency. All women recreationally active at high altitudes should be made aware of the signs of altitude sickness (headache, poor sleep, anorexia, fatigue, nausea, vomiting, and, in severe cases, pulmonary edema). They should stop exercising, return to a lower altitude as soon as possible, and seek medical attention if such symptoms occur. (See "High altitude illness: Physiology, risk factors, and general prevention" and "Prenatal care: Patient education, health promotion, and safety of commonly used drugs", section on 'Travel to moderate and high altitudes'.)

Frequency and duration of exercise — For health benefits, most guidelines recommend pregnant women engage in at least 30 minutes of exercise at least five to seven days per week [11,73-77]. Pregnant women who have not been regular exercisers should follow a gradual progression of increasing the duration of exercise and can begin with as little as 10 minutes.

There are minimal data on the safe upper limit for the duration of exercise in pregnancy, and intensity must also be considered in this assessment (see 'Intensity of exercise' below). In general, fit pregnant women who want to engage in prolonged exercise (over 45 minutes of continuous exercise) should exercise in a thermoneutral environment or in controlled environmental conditions (air conditioning), with attention to proper hydration and subjective feelings of heat stress.

Intensity of exercise — Prescription of exercise intensity in pregnancy is individually tailored to the individual's level of physical ability, ideally involves easily quantified activities (eg, walking, swimming, stationary cycling), and is increased gradually. A reasonable approach for previously sedentary women is to initially engage in low- to moderate-intensity exercise (casual to brisk walk and low-intensity workouts), increasing the intensity gradually. Although an upper level of safe exercise intensity in pregnancy has not been established, we believe that women who were regular exercisers before pregnancy and who have uncomplicated, healthy pregnancies should be able to engage in high-intensity exercise programs (eg, jogging, aerobics) with no adverse effects [2,3,77].

Exercise intensity can be monitored based on perceived exertion, heart rate, or metabolic equivalents (METs). When exercise is self-paced, most pregnant women (including athletes) will voluntarily reduce their exercise intensity as pregnancy progresses [11]. Athletes should expect overall activity and fitness levels to decline somewhat as pregnancy progresses [11,75]; however, improving athletic performance in pregnancy is possible [13,78], with medical guidance and clearance.

●Monitoring perceived exertion – The use of perceived exertion appears to be the most practical method of gauging exercise intensity [3,11]. For moderate exercise, ratings of perceived exertion should be 13 to 14 (somewhat hard) on a Borg Rating of Perceived Exertion scale, where 6 represents no exertion and 20 represents maximal exertion [79].

Even simpler and more practical is the "talk test," in which the individual should be able to carry on a normal conversation with moderate exercise intensity. By comparison, vigorous exercise is associated with substantial increases in breathing, inability to carry on a normal conversation easily, and perspiration.

●Monitoring heart rate – "Fit" women, such as elite athletes, who wish to use heart rate to gauge exercise intensity to maintain physical fitness can use the following heart rate training zone reference as a guide [2,4,80,81]:

•Age 20 to 29 years – 145 to 160 beats/minute

•Age 30 to 39 years – 140 to 156 beats/minute

Target training heart rate recommendations for pregnant women vary by country [77] and exercise intensity (eg, "light" versus "moderate" versus "vigorous" [4]). They are not widely used. Available data are limited because exercise studies conducted on pregnant women lack controls and standardization, ignore fitness level or estimate it based on maximal oxygen consumption data, and do not distinguish between weight-bearing and non-weight-bearing exercise [81,82].

●Monitoring METs – Nonpregnant individuals are advised to participate in regular moderate-intensity exercise routines defined as exercise of 3 to 4 METs or any activity that is equivalent in difficulty to brisk walking [11,53]. In the absence of medical or obstetric complications, there is no reason to alter this recommendation for pregnant women. Moderate exercise appears to be an appropriate goal for the two-thirds of pregnant women who have not been engaging in regular exercise prior to pregnancy.

Based on our experience, exercise intensity can be safely increased to 6 to 7 METs in well-conditioned healthy women (walking 3.5 miles per hour uphill is 6 METs) (table 4) [11]. A combination of moderate and more vigorous exercise usually results in an improvement in fitness.

Hydration and energy — Dehydration is a risk with intense or prolonged exercise or exercise in a hot environment; appropriate hydration before, during, and after exercise is important in these settings. Any loss of weight during an exercise session is fluid loss that should be made up before the next exercise session (1 pound [0.45 kg] weight loss equals approximately 1 pint [16 ounces (United States)] of fluid [0.5 L]).

A healthy diet and adequate gestational weight gain are important and are reviewed separately (see "Nutrition in pregnancy: Dietary requirements and supplements" and "Gestational weight gain"). The caloric costs of exercise should be estimated and balanced by appropriate caloric intake before engaging in prolonged or strenuous exercise. In addition, women should be aware of hypoglycemia symptoms so they can rapidly consume a fast-acting carbohydrate (eg, fruit, crackers, candy). In a study that compared glucose homeostasis in nonpregnant women and the same women in the third trimester during one hour of exercise on a stationary bicycle at 55 percent VO₂max, blood glucose levels decreased at a faster rate in pregnancy and approached hypoglycemic levels (below 70 mg/dL [3.9 mmol/L]) after 45 minutes of continuous moderate-intensity exercise [83].

Ketonuria is detected occasionally in women who exercise vigorously or for a prolonged period of time. Ketonuria indicates a catabolic state and can occur in anyone who has a negative caloric balance. A small degree of ketonuria in pregnant women is unlikely to be associated with any measurable deficits in the newborn [84,85].

When to stop exercising — A pregnant woman should stop exercising promptly and call her health care provider if she has any of the following warning signs of a potential problem [3]:

●Vaginal bleeding

●Abdominal pain with or without nausea

●Regular painful contractions

●Amniotic fluid leakage

●New dyspnea before exertion

●Dizziness, syncope

●Headache

●Chest pain

●Muscle weakness affecting balance

●Calf pain or swelling

The exercise routine should be reassessed as clinically indicated.

SPECIAL POPULATIONS — Pregnant women who are elite/competitive athletes and those with diabetes, severe obesity, or hypertension are counseled on an individual basis. Modified exercise routines, closer pregnancy supervision, and additional testing may be indicated.

Elite/competitive athletes — Competitive athletes, in the absence of developing maternal or fetal side effects/complications, may maintain a more strenuous training schedule under supervision throughout pregnancy and resume high-intensity postpartum training sooner than most recreational athletes. The concerns of the pregnant, competitive athlete fall into two general categories: effects of pregnancy on competitive ability and effects of strenuous training and competition on the fetus and pregnancy.

Available data suggest that a woman's aerobic fitness remains the same or improves slightly during pregnancy if she continues to exercise [2]. Interestingly, at least 17 athletes have competed at the Olympics while pregnant and a few have medaled [86].

A systematic review found that elite pregnant athletes maintained 4 to 13 hours of training per week [87]. Most elite athletes will decrease their pace of training during pregnancy. As pregnancy progresses, weight gain, physiologic anemia, edema, and musculoskeletal changes and pain can prevent the athlete from maintaining her prepregnancy level of performance, but this depends on the specific requirements of her sport [88,89]. For example, a tennis player may be less able to rapidly stop and start or change direction. Attempts to substitute compensatory movements for finely tuned skilled movements will, at the very least, result in inefficient movement and decrease competitive performance, and may also increase the risk of injury. One-third of injuries recorded in pregnancy have been attributed to physical activities and exercise; in one study, the reported incidence was 4.1/1000 hours of exercise [90]. Ligament laxity and increased stress on the joints and spine, particularly during weight-bearing exercise, may predispose pregnant athletes to sprains. (See "Maternal adaptations to pregnancy: Musculoskeletal changes and pain".)

Elite female athletes who maintain the same high-intensity training in pregnancy are also at risk for "overtraining syndrome." Although not reported in pregnancy, clinicians attending elite athletes should be aware of this complication, which presents with excessive and more rapid manifestation of fatigue, sleep disorders, lack of weight gain, increased frequency of musculoskeletal injuries, and persistent tachycardia at rest. (See "Overtraining syndrome in athletes".)

Based on low-quality evidence, it appears prudent for elite female athletes to avoid strenuous exercise in the week after ovulation and avoid repetitive heavy lifting during the first trimester, as these activities may increase the risk of miscarriage [5]. A Finnish case control study of physiotherapists reported an odds ratio of 3.5 (95% CI 1.1-9.0) between occupational heavy lifting and spontaneous abortion [91]. Heavy lifting in pregnancy has been arbitrarily defined in the literature as between 10 to 20 kg (22 to 44 lb) more than 20 times/week [65].

Pregnant elite athletes may use perception of exertion or fatigue to gauge their training intensity, similar to other pregnant women (see 'Intensity of exercise' above). Those who have access to monitoring equipment are advised to refrain from training at intensities >90 percent of their VO₂max, although this is not based on data [48].

No studies have evaluated pregnancy duration in elite athletes. Anecdotal information suggests that strenuous training does not cause preterm labor or delivery. However, a competitive athlete with a history of preterm labor should consider either decreasing training or discontinuing training during pregnancy, given the absence of strong data indicating that strenuous exercise has no impact on length of gestation in women at risk for preterm birth [92].

Dehydration may provoke uterine contractions, so particular attention should be paid to maintaining proper hydration during and between high-intensity, prolonged exercise sessions and exercise in hot, humid weather. Fluid balance during an exercise session can be monitored by self-weighing before and after the session. (See 'Hydration and energy' above.)

Because training in elite athletes is likely to be high-intensity, prolonged, and frequent, it is likely that gestational weight gain and fetal growth will be less than for sedentary individuals. One study of endurance athletes observed significant reductions in birth weight, which was attributed to decreased neonatal fat mass [93]. A competitive athlete with a small for gestational age infant (past or current pregnancy) or at risk for a small for gestational age infant because of pregnancy complications should consider either decreasing training or discontinuing training during pregnancy in consultation with an obstetrician or maternal-fetal specialist.

Participation in competitive sports at the elite level does not appear to affect delivery outcome, including length of labor, frequency of intrapartum cesarean delivery, and severe perineal tears [94]. Available data are not sufficient to determine whether the type of activity (eg, low impact versus high impact) affects outcome. It has been hypothesized that high-impact sports might increase pelvic floor muscle strength and volume, which might in turn affect the length of the second stage, fetal rotation, and risk of perineal injury [95,96].

Women with or at risk for diabetes — Exercise is increasingly promoted as an intervention to reduce the risk of gestational diabetes or as part of the therapeutic regimen for nonpregnant individuals with diabetes mellitus. In addition to its cardiovascular benefits, exercise can also improve glycemic control, which largely results from increased tissue sensitivity to insulin. (See "Effects of exercise in adults with diabetes mellitus".)

Exercise may also help to reduce the risk of developing gestational diabetes or improve glucose control in women with gestational or pregestational diabetes. The author advises overweight, sedentary pregnant women with pregestational diabetes to engage in a minimum of 15 metabolic equivalent (MET) hours of physical activity per week, preferably building up to ≥28 MET hours of physical activity per week to improve glycemic control [97,98].

The author similarly advises overweight, sedentary pregnant women without diabetes to engage in regular exercise to reduce their risk of developing gestational diabetes. Non-weight-bearing exercise (eg, stationary bicycle) can be sustained longer at higher intensity and may be more effective for previously sedentary pregnant women. One study that performed measurements by indirect calorimetry suggested preferential carbohydrate utilization during this type of activity, independent of fitness level and weight [49]. (See "Gestational diabetes mellitus: Screening, diagnosis, and prevention", section on 'Lifestyle interventions for risk reduction' and "Gestational diabetes mellitus: Glycemic control and maternal prognosis", section on 'Exercise'.)

Obese women — Clinical trials under medical supervision have demonstrated that lifestyle intervention for weight-gain restriction and moderate exercise can be safely prescribed for obese pregnant women [99]. Despite methodologic pitfalls in these studies, the evidence suggests overweight/obese pregnant women who exercise and follow a judicious diet can reduce their risks for developing gestational diabetes and preeclampsia, avoid excessive gestational weight gain (table 5), and increase the likelihood of a newborn of normal birth weight [14,100]. (See "Gestational weight gain".)

Women at increased risk for miscarriage or preterm birth — For most pregnant women, physical activity/exercise does not increase the risk of miscarriage or preterm delivery, and bed rest does not reduce the risk of miscarriage or preterm delivery. However, studies on exercise in pregnancy have generally excluded women at high risk of miscarriage or preterm birth.

Given the absence of reassuring data in high-risk women, we agree with expert opinion that pregnant women at high risk for miscarriage or preterm birth (eg, multiple gestation) should limit high levels of exercise/physical activity, particularly activities involving strength training and heavy lifting [64,101]. Very few conditions in pregnancy require strict or modified bed rest; these include preeclampsia with severe features and some cases of preterm prelabor rupture of membranes. (See 'Choosing an exercise program' above.)

The safety of maternal exercise in twin pregnancy is a common concern and has not been systematically studied since multiple gestations are at high risk for preterm labor and exercise can cause increased uterine activity and trigger preterm labor. Worldwide, most organizations list twins and other multiple gestations as a contraindication to exercise. In the author's practice, he suggests such patients engage in non-weight-bearing exercises, such as swimming; counsels them about awareness of increased uterine activity; and uses office ultrasound to periodically measure cervical length to detect shortening. (See "Short cervix before 24 weeks: Screening and management in singleton pregnancies".)

Women at increased risk for fetal growth restriction — As discussed above, women with low-risk pregnancies who regularly participated in a supervised prenatal exercise program appeared to have a clinically insignificant reduction in birth weight [23]. (See 'Risks' above.)

The effect of exercise in women at high risk for fetal growth restriction (eg, previous pregnancy with growth restriction) is unknown. Given the lack of clear evidence of safety in this subgroup, it is prudent for women who exercise regularly and are at high risk of fetal growth restriction to reduce their level of exercise in the second and third trimesters, in addition to standard monitoring of fetal growth.

Postpartum women — The physiologic and anatomic changes of pregnancy generally return to the prepregnancy state by approximately six to eight weeks postpartum.

Exercise and a healthy diet postpartum promote weight loss, which can improve or prevent many future obesity-related risks, such as diabetes mellitus and hypertension. (See "Obesity in adults: Role of physical activity and exercise", section on 'Health benefits associated with exercise'.)

A decreased frequency of postpartum depression has been associated with return to physical activity following pregnancy [102], as long as the exercise is stress-relieving and not stress-provoking [103]. Although an inverse association between physical activity and depression has been reported across different geographical regions and age groups in nonpregnant populations [104], randomized trials in pregnant women have not demonstrated a significant benefit; however, adherence is a challenge during this time [105,106]. (See "Postpartum unipolar major depression: Epidemiology, clinical features, assessment, and diagnosis".)

After vaginal delivery — The appropriate time to return to a routine level of prepregnancy physical activities varies and depends on many factors, including the degree of perineal trauma, blood loss (degree of anemia), presence of medical/surgical complications related to pregnancy and the postpartum period, and personal preference. After a vaginal delivery, most women should resume their normal physical activities at their own pace and in consultation with their medical provider. Professional athletes who want to resume their regular training schedule should do so under medical supervision, with consideration of the athlete’s personal performance, childbirth experience, and lactation and sport demands [107,108]. Whether pelvic floor function is impacted by a rapid return to postpartum physical activity has not been determined definitively, but data from a randomized trial suggest that allowing women to rapidly resume their normal activities after reconstructive pelvic surgery improves pelvic floor outcomes compared with restricted postoperative activity [109].

Kegel pelvic floor muscle exercises several times per day, as tolerated, can reduce postpartum urinary and anal incontinence. They can be started in the first or second week after delivery in women who have not experienced lacerations or episiotomy. (See "Fecal and anal incontinence associated with pregnancy and childbirth: Counseling, evaluation, and management", section on 'Postpartum individuals with FI/AI' and "Pelvic organ prolapse in females: Epidemiology, risk factors, clinical manifestations, and management", section on 'Pelvic floor muscle exercises' and "Effect of pregnancy and childbirth on urinary incontinence and pelvic organ prolapse", section on 'Prophylactic pelvic floor muscle exercises'.)

After cesarean delivery — Early ambulation and return to normal prepregnancy physical activities and exercise routines as soon as medically safe could reduce comorbidities associated with a postsurgery sedentary lifestyle [110,111] and appears to enhance restoration of physical function after orthopedic and other surgeries [112]. Although there are scant data to guide any postoperative activity recommendations, and lack of consensus among surgeons [113], the presence of the following factors should delay resumption of some or all physical activities [76,114]:

●Medical complications (eg, anemia, cardiorespiratory disorders, thromboembolism)

●Pain and need for analgesia

●Surgical and postoperative complications (eg, nausea/vomiting, abnormal wound healing, neuropathy, incontinence)

Recreational and elite athletes, in particular, tend to be eager to regain prepregnancy fitness levels, given that cessation of training for three to four weeks decreases endurance performance by 4 to 25 percent [115]. Most women will be able to resume training 4 to 6 weeks after surgery. However, rapid resumption of physical activities should be individualized and occur only after medical clearance, which should establish symptom-free and/or controlled stable vital signs, reactivation/stabilization and ability to control muscle functions, and restoration/stabilization of motor skills.

Exercise prescription — After medical clearance, we suggest the following exercise prescription after cesarean.

●During pregnancy and the first three weeks after delivery

•A walking program, initially at least 10 minutes/day several times a day, and progress, as tolerated, to regain cardiorespiratory fitness. Women who regularly exercised at a moderate or high level during pregnancy can gradually begin endurance training, beginning with low-impact activities to minimize pressure on the pelvic floor [48].

•Use of stairs at home with assistance at slow pace and increased frequency, as tolerated.

•Lifting – The American College of Obstetricians and Gynecologists recommends, after cesarean delivery, temporary abstinence from lifting objects heavier than the newborn [116]. In this author's experience, women who engaged in muscle strengthening activities prior to and during pregnancy have the ability to lift objects heavier than recommended without difficulty or consequences. Muscle strength is a function of muscle mass and previous training: A 15- to 30-day detraining period can lead to significant muscle atrophy; as such, additional restrictions can only lead to further muscle loss and detraining [117]. However, safe upper limits have not been established; thus, caution should be exercised.

The concern about the integrity of the abdominal wall and potential negative effect of increased intraabdominal pressure during Valsalva or during heavy lifting after laparotomies has been refuted in small studies, suggesting that increased intraabdominal pressure occurs more frequently during unavoidable activities like standing from a seated position rather than Valsalva [118]. (See "Complications of abdominal surgical incisions", section on 'Lifting'.)

For advanced recreational or elite athletes, the wound healing process of the abdominal wall will determine the timing for return to more strenuous type of exercises. The abdominal fascia regains 51 to 59 percent of its original tensile strength at 42 days, 70 to 89 percent at 120 days, and 73 to 93 percent by 140 days [119]. Individual responses after abdominal surgeries vary, and moderation is appropriate until the patient is free of pain or other symptoms.

●Weeks 3 to 6 after delivery – Significant lordosis, low back pain, or joint laxity will require a longer recovery time and a modified exercise routine. Wound conditions, the degree of abdominal wall laxity, and rectus abdominis diastasis may interfere with physical activity and exercise; some patients may benefit from use of an abdominal binder during the first few sessions.

•To regain abdominopelvic strength and tone, a core and/or total body exercise routine is effective.

•In addition, Kegel pelvic floor muscle exercises performed several times per day, as tolerated, can reduce postpartum urinary and anal incontinence. They can be started before week 3 as long as contracting the pelvic floor is not painful. (See "Fecal and anal incontinence associated with pregnancy and childbirth: Counseling, evaluation, and management", section on 'Postpartum individuals with FI/AI' and "Pelvic organ prolapse in females: Epidemiology, risk factors, clinical manifestations, and management", section on 'Pelvic floor muscle exercises' and "Effect of pregnancy and childbirth on urinary incontinence and pelvic organ prolapse", section on 'Prophylactic pelvic floor muscle exercises'.)

●Week 6 and beyond

•At six weeks postpartum, women should aim to follow the Physical Activity Guidelines for Americans, which recommend that all adults engage in at least 150 to 300 minutes of moderate-intensity physical activity per week [120]. (See "The benefits and risks of aerobic exercise".)

•Women who, prior to their pregnancies, engaged in gym/club-apparatus activities may slowly and cautiously resume these activities using low settings on the equipment. Joints and ligaments may require as much as three months to return to prepregnancy configuration.

Breastfeeding women — Women who exercise to moderate levels of exertion do not have changes in breast milk quantity or composition or infant acceptance of breast milk; however, exercise at maximal levels has been associated with significant but short-term elevations in lactic acid in breast milk and less infant acceptance [121-125]. Nursing before exercise avoids the potential problems associated with increased acidity of breast milk and also avoids the discomfort of engorged breasts while exercising [125].

Modest weight reduction while nursing appears to be safe and does not compromise neonatal weight gain [121-124]. In a 2012 meta-analysis (four randomized trials, n = 170 women 3 to 16 weeks postpartum), maternal exercise programs of 11 days, 10 weeks, 12 weeks, or 16 weeks duration did not significantly reduce infant weight gain compared with a variety of control programs [124]. Most of these women had previously been sedentary. In strenuously training mothers, anecdotal reports have described failure of infants to gain weight as rapidly as expected. It is possible that inadequate fluid or nutritional intake in vigorously exercising mothers, rather than exercise itself, led to decreased milk production, resulting in suboptimal infant weight gain.

GUIDELINES FROM SELECTED NATIONAL ORGANIZATIONS — A comparison of guidelines for physical activity from around the world for pregnant women revealed consensus that physical activity in pregnancy is beneficial to most women and has minimal risks, but may require some modifications to accommodate the normal maternal anatomic and physiologic changes and fetal requirements [77,114].

There was also close to universal consensus that certain maternal, fetal, or environmental conditions are absolute or relative contraindications for exercise in pregnancy. Among these conditions are significant or active cardiovascular disease, restrictive lung disease, poorly controlled thyroid disease, multiple gestation (triplets or higher), preeclampsia, premature labor and premature rupture of membranes, severe anemia, poorly controlled type I diabetes, persistent bleeding, extreme obesity, and extreme underweight.

Links to several society and government-sponsored guidelines are provided through the following section.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Exercise in adults".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topic (see "Patient education: Activity during pregnancy (The Basics)")

SUMMARY AND RECOMMENDATIONS

●We agree with recommendations of major medical societies that women with uncomplicated pregnancies should be encouraged to exercise as part of a healthy lifestyle before, during, and after pregnancy. (See 'Guidelines from selected national organizations' above.)

●Exercise during pregnancy has minimal risks and demonstrated benefits for most pregnant women, including maintenance or improvement of physical fitness, control of gestational weight gain, reduction in low back pain, and possibly a reduction in risk of developing gestational diabetes or preeclampsia. Moderate exercise is not a direct cause of any adverse pregnancy outcome; however, pregnant women may be at greater risk of injuries to joints, falling, and significant abdominal trauma during certain types of exercise. Abdominal trauma can result in placental abruption, which can lead to fetal death or morbidity. (See 'Benefits and risks' above.)

●Prior to participation in an exercise program, pregnant women should be evaluated for medical and obstetric contraindications to exercise. (See 'Pre-exercise and ongoing risk assessment' above.)

●Some sports should be avoided in pregnancy (table 3). Contact sports and physical activities in which the risk of falls/trauma is high are a concern in pregnancy because of the risk of fetal harm from maternal trauma. SCUBA diving should also be avoided because of the potential for fetal harm. (See 'Choosing an exercise program' above.)

●Maintenance of euhydration is particularly critical to heat balance during prolonged exercise and exercise in hot, humid weather; hyperthermia in very early pregnancy may increase the risk for neural tube defects. The caloric costs of exercise should be estimated and balanced by appropriate caloric intake and awareness of hypoglycemia symptoms. (See 'Hydration and energy' above and 'Risks' above.)

●The intensity, frequency, and duration of exercise depend on patient-specific factors. For most healthy pregnant women, the following exercise prescription is reasonable: moderate-intensity exercise (able to carry on a normal conversation during exercise) that includes aerobic exercise and strength training, performed for 30 minutes daily, five to seven days per week.

Previously sedentary women should begin with 10 to 20 minutes of continuous low-intensity exercise three times per week, increasing the intensity, frequency, and duration gradually.

Physically active women can engage in moderate to vigorous physical activity. They should strive to maintain a good fitness level throughout pregnancy without trying to reach their peak fitness level or train for athletic competition. (See 'Exercise prescription' above.)

●We advise women at high risk for preterm birth or fetal growth restriction who exercise to reduce their level of exercise in the second and third trimesters. (See 'Women at increased risk for miscarriage or preterm birth' above and 'Women at increased risk for fetal growth restriction' above.)