Sweating it out: Exercise in pregnancy

“Is it OK for me to work up a sweat during pregnancy?” The answer is a resounding yes! Exercise during pregnancy is safe and recommended for most patients, as it teems with beneficial effects throughout gestation and the postpartum period.

Music and business icon Rihanna went viral on the internet when she became the first outwardly pregnant woman in history to perform solo at the 2023 Super Bowl half-time show. As she did so, Google searches for “pregnant workouts” increased by 5000%.1 Motivation to implement healthy lifestyle modifications increases in pregnancy,2 and general interest in having an active pregnancy currently abounds. This could not come at a more vital time since, according to 2017-2018 National Health and Nutrition Examination Survey data, 42% of women are obese and 27.5% are overweight.3

This article will review the benefits and safety of exercise in pregnancy, the potential harms of activity restriction, and the recommendations from the American College of Obstetricians and Gynecologists (ACOG) on physical activity in pregnancy.

Benefits of exercise in pregnancy

Exercise can improve multiple pregnancy outcomes (Box). First, exercise reduces the incidence of gestational diabetes. It increases the rate of glucose uptake by skeletal muscle, thereby improving glucose tolerance. Data from meta-analyses demonstrate a reduction of gestational diabetes by 42% in patients of normal weight and 39% in patients who are overweight or obese who engage in regular aerobic exercise.4,5 This is of additional importance because patients with gestational diabetes are at greater risk for developing type 2 diabetes mellitus later in life.

Second, exercise reduces the rates of hypertensive disorders of pregnancy. A systematic review of 7 randomized controlled trials including 2500 patients showed that consistent aerobic exercise starting prior to 23 weeks’ gestation decreased the incidence of gestational hypertension by 46% and preeclampsia by 21%.5

Exercise also helps to lower preterm birth rates. Patients who are obese or overweight who engaged in regular physical activity beginning before the second trimester had a 38% decrease in preterm birth compared with those who were inactive.6 Data in patients of normal weight have shown no difference in preterm birth, which highlights that exercise is not associated with an increased risk for preterm delivery either.7

Psychological health also improves with exercise. Data from large systematic reviews of patients with and without baseline depression show that regular physical activity decreases the odds of antenatal depression by 67%, the severity of antenatal depressive symptoms by 38%,8 and the frequency of postpartum depression symptoms by 60%. It also lowers postpartum depression screening scores overall.9

Furthermore, there are more favorable delivery-related outcomes. In randomized trials, data have shown that regular exercise reduces the rate of cesarean birth by 31% compared with that of sedentary controls.10 In those patients who deliver vaginally, the second stage of labor was shorter and the adjusted likelihood of an intact perineum was 8.5 times higher.11 Regardless of the mode of delivery, regular exercise was shown to shorten postpartum recovery time (measured as time to returning to several household chores) by 1.5 days for vaginal birth and 6 days for cesarean birth.12

Lastly, physical activity in pregnancy intuitively improves global markers of cardiorespiratory fitness. Patients see gains in muscular strength and endurance, flexibility, agility, coordination, balance, power, reaction time, and body composition. Constipation is eased, and due to decreased excessive gestational weight gain, patients have less back pain and postpartum weight retention.

Safety of exercise in pregnancy

Physical activity in pregnancy is associated with minimal risk as evidenced by data from studies on the fetal effects of maternal exercise. Regular physical activity does not increase the risk for low birth weight or stillbirth.13 A moderate increase in fetal heart rate by 10 to 30 beats per minute over baseline is seen during or after exercise.14 There are no deleterious changes in biophysical profiles with moderate-intensity exercise.14 Even in strenuous exercise, no changes are seen in these indices in most patients. In a study of 6 Olympic-level athletes at 23 to 29 weeks’ gestation, when maternal heart rate exceeded 90% of maximum, fetal heart rate was reassuring within 10 minutes.15 However, in a subset of highly active athletes, patients may push beyond a threshold intensity at which fetal wellbeing is compromised. It is possible that an absolute intensity or duration (or both) exists beyond which fetal risk ensues, but this remains ill-defined.

Detriments of activity restriction

Despite data for benefit, activity restriction is one of the most common interventions recommended for the treatment of preterm labor and prevention of preterm birth. There is no standard definition for activity restriction. Strict activity restriction is often used synonymously with bed rest, but other forms of activity restriction may include cessation from exercise, heavy lifting, or employment, or pelvic rest. Given varying usages of the term, current estimates of activity restriction are unknown, but in the past, nearly 20% of patients had been prescribed activity restriction at some point in their pregnancy.16 However, a plethora of research findings show that strict activity restriction (bed rest) not only does not prevent adverse obstetrical outcomes, but it confers significant physical and psychosocial risks.

Multiple studies have evaluated the ineffectiveness of activity restriction in reducing preterm birth rates. A secondary analysis of the National Institute of Child Health and Human Development Maternal-Fetal Medicine Units Network Preterm Prediction Study that included 1100 patients deemed high risk for preterm delivery (defined as presence of contractions, positive fetal fibronectin, cervical length 17 In data from a randomized trial of 73 patients between 23 and 34 weeks’ gestation who were admitted for management of threatened preterm labor without delivery, there were no differences in preterm delivery, delivery within 1 or 2 weeks, overall pregnancy prolongation, or neonatal outcomes between patients randomly assigned to strict bedrest compared with those with no activity restriction.18

Regarding quantitative activity assessments, findings from a prospective trial of 134 healthy nulliparas who wore a wrist pedometer continuously from 10 to 24 weeks’ gestation until delivery without modifying activity levels based on clinician guidance demonstrated that patients with low activity levels (3500 steps per day).19 Additionally, in a double-blinded pilot study of 50 patients hospitalized for risk for preterm delivery (defined as cervical length ≤ 20 mm or cervical dilation) who were discharged wearing smart band activity trackers with no specific recommendations for activity levels, data showed an inverse relationship between median number of steps per day and risk for preterm birth, with patients who delivered preterm taking 1000 fewer steps per day than those who delivered at term.20

Furthermore, activity restriction has numerous other detrimental health effects involving multiple organ systems that are evident within just a few days of immobility (Table).21 On top of cardiorespiratory deconditioning, increased insulin resistance, and a more prothrombotic state, patients experience decreases in bone mineral density, muscle atrophy, inadequate maternal weight gain, lower infant birth weight, and skin breakdown. Prolonged activity restriction and hospitalization are also associated with maternal stress, anxiety, and depression due to separation from one’s family, significant financial costs, and resultant loss of wages and productivity.

Thus, the Society for Maternal-Fetal Medicine and Choosing Wisely published a strong recommendation against the “routine use of any type of activity restriction” for pregnant patients 1) at risk of preterm birth based on preterm labor symptoms, arrested preterm labor, or cervical shortening; 2) with multiple gestation; or 3) for the treatment of fetal growth restriction, preterm prelabor rupture of membranes, or hypertensive disorders of pregnancy.22,23

ACOG recommendations for physical activity in pregnancy

Guidelines from ACOG indicate that patients with uncomplicated pregnancies should be encouraged to engage in aerobic and strength-conditioning exercises before, during, and after pregnancy.24 Clinicians should evaluate patients with medical or obstetric complications prior to making recommendations about participating in physical activity during pregnancy (validated tools such as the Get Active Questionnaire for Pregnancy by the Canadian Society for Exercise Physiology25 exist to assist in assessment). It is important to note that there are few maternal medical conditions in which aerobic exercise is absolutely contraindicated. However, regular exercise is not recommended in patients with hemodynamically significant heart disease, restrictive lung disease, prolapsing membranes, or persistent vaginal bleeding.

Pregnant women are advised to engage in at least 150 minutes of moderate-intensity aerobic physical activity, strength training, pelvic floor training, and gentle stretching spread over at least 3 to 4 days per week, beginning in the first trimester(Figure26,30). Moderate intensity can be gauged in 1 of 3 ways: a score of 12 to 14 on the Borg Rating of Perceived Exertion scale; target heart rate ofless than 60% to 80% of maximum heart rate (calculated as 220 minus the person’s age); or, more practically, the talk test, in which carrying on a conversation (but not singing) is still possible. Patients who habitually engaged in vigorous-intensity aerobic activity or who were physically active before pregnancy can continue these activities during pregnancy and the postpartum period.

Some modification to exercise routines may be necessary due to normal anatomic and physiologic changes of pregnancy. A persistent supine position during exercise beyond 20 weeks’ gestation should be avoided because aortocaval compression by the gravid uterus reduces venous return leading to hypotension. Also, due to a physiologic decrease in pulmonary reserve, the ability to exercise anaerobically is impaired (anaerobic exercise involves quick bursts of energy performed at maximal effort for a short time such as sprinting, jumping, or high-intensity interval training). Therefore, aerobic training should be prioritized, which increases aerobic capacity.

Several types of exercises have been vetted as safe and beneficial in pregnancy. These include walking, stationary cycling, dancing, resistance training, stretching, and water aerobics. Patients should avoid activities with a high risk of abdominal trauma or imbalance such as collision sports, horseback riding, downhill skiing, off-road cycling, gymnastics, or sky diving. Scuba diving should also be avoided due to the inability of the fetal pulmonary circulation to filter bubble formation. Patients who live at sea level can safely exercise at altitudes up to 6000 feet. Temperature regulation is highly dependent on hydration and environmental conditions. Patients should stay well hydrated, wear loose-fitting clothing, and avoid high heat and humidity to protect against heat stress (eg, hot yoga), especially in the first trimester (although exercise would not be expected to increase core body temperature to the range of concern for neural tube defects).

Data on appropriate limits for weight training are lacking. Some experts suggest avoiding frequent, heavy weightlifting such as training to failure. A survey of 679 pregnant patients who continued heavy (≥80% of their 1-repetition maximum) prenatal resistance training showed no increase in adverse perinatal outcomes such as preterm delivery or cervical insufficiency, but had a heightened prevalence of postpartum urinary incontinence compared with the general population (57% vs 32%; however, the rate of urinary incontinence was similar to that of nonpregnant active women who participate in high-impact resistance training).27 Open glottis breathing can be utilized to help reduce Valsalva, and contracting the pelvic floor muscles before and during heavy lifting can counteract the impact on the pelvic floor from increased intra-abdominal pressure.

Exercise should be discontinued if a patient experiences vaginal bleeding, regular painful contractions, amniotic fluid leakage, dizziness, headache, chest pain, dyspnea, or muscle weakness that affects balance.

Conclusions

Physical activity helps to reduce the rate of adverse obstetric outcomes such as gestational diabetes, hypertensive disorders of pregnancy, preterm birth, cesarean birth, and postpartum depression. Available data show no benefit to activity restriction, so it should not be routinely prescribed for patients at risk for preterm birth. And it is recommended for most patients to engage in at least 150 minutes of moderate-intensity aerobic exercise and strength training per week for maximal benefit.

References

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