Gestational Diabetes During and After Pregnancy

17. Exercise Recommendations in Women with Gestational Diabetes Mellitus

Raul Artal , Gerald S. Zavorsky and Rosemary B. Catanzaro

(1)

Department of Obstetrics, Gynecology and Women’s Health, Saint Louis University, St. Louis, MO, USA

Raul Artal

Email: artalr@slu.edu

Abstract

Experts agree that pregnancy and postpartum are valuable periods during which to undertake proactive and preventative health care of modifiable risk factors through physical activity. In this chapter, we review the physiologic rationale for exercise during GDM and for GDM prevention, studies addressing these topics, and current recommendations for physical activity regarding GDM. We also suggest modifications to the current recommendations based on the data presented.

17.1 Introduction

This chapter provides the physiological background of exercise prescription for pregnant patients affected by gestational diabetes mellitus (GDM) and type 2 diabetes. Also included is a review of the pertinent literature. The American College of Obstetricians and Gynecologists (ACOG) and the American Diabetes Association (ADA) have endorsed exercise as “a helpful adjunctive therapy” for GDM.12 Exercise protocols for women with GDM or for GDM prevention are underutilized due to provider’s reluctance to prescribe exercise as well as lack of patient compliance.

Pregnancy has been characterized as a diabetogenic event brought about by hormones with diabetogenic effects (estrogen, human placental lactogen also called human chorionic somatomammotropin (HPL), cortisol, and progesterone). The diabetogenic effects of these hormones lead to insulin resistance and increased insulin requirements. During pregnancy, catabolic stress hormones trigger an increase in metabolism with wide shifts between the fed and fasting states.3 In pregnancy, fasting blood glucose is lower, but as a result, postprandial gluconeogenesis causes glucose levels to increase. To modulate the increase in glucose levels, an increase in insulin secretion occurs throughout gestation. Despite counter-regulatory processes, patients with GDM experience increased fat storage and adipocyte hypertrophy and hyperplasia resulting in decreased insulin sensitivity. The impaired insulin sensitivity in patients with GDM results in decreased glucose uptake by muscles and splanchnic organs, whereas hepatic glucose production is enhanced.

While dietary strategies are a mainstay of treatment to optimize pregnancy outcomes, up to 39% of GDM women cannot be managed with diet alone.4 Many of these patients will experience fasting or postprandial hyperglycemia, or both, despite dietary interventions. Although insulin corrects the hyperglycemia, it does not affect peripheral insulin resistance. Thus, the logical intervention would be exercise, which will decrease insulin resistance.

Physical activity improves glucose tolerance through at least two mechanisms: (1) improved insulin sensitivity, primarily through insulin-stimulated muscle glucose uptake, which in turn is directly related to energy expenditure, and (2) insulin-independent mechanisms directly related to glucose transportation (GLUT4).

It is well established that regular exercise training improves insulin sensitivity and insulin-stimulated muscle glucose uptake in type 2 diabetes patients.5 Insulin sensitivity is defined as the concentration of insulin required to cause 50% of its maximal effect on glucose transport.6 Some of the purported mechanisms include training-induced enhancement of the insulin-mediated increase in muscle blood flow and glucose extraction from blood.5 Insulin sensitivity is increased 12–48 h after a single exercise session in both healthy711 and insulin resistant subjects,912,13 but this effect is lost after 3–6 days of inactivity.1417 However, in well-trained subjects, a single bout of exercise can improve insulin sensitivity. In one study, eight well-trained subjects stopped training for 10 days.18 The maximum rise in plasma insulin concentration in response to a 100-g oral glucose load was 100% higher after 10 days without exercise than when the subjects were exercising regularly. Despite the increased insulin levels, blood glucose concentrations were higher after 10 days without exercise. One bout of exercise after 11 days without exercise returned insulin binding and the insulin and glucose responses to an oral 100-g glucose load almost to the initial “trained” value. These results demonstrate that bouts of exercise play an important role in insulin sensitivity.18

Studies suggest that insulin sensitivity after a single bout of exercise is negatively related to energy expenditure. In one study,11 30 nonobese subjects exercised on a treadmill at 2.0 L/min (60% of aerobic capacity) for 30–120 min. It was demonstrated that the exercise-induced changes in homeostasis model assessment of insulin resistance (HOMA-IR) was negatively and curvilinearly correlated to energy expenditure (r = −0.67, p = 0.001). HOMA-IR decreased by 30% compared to preexercise in subjects who expended more than 900 kcal during the exercise bout.11

Glucose uptake is also partially regulated via insulin-independent mechanisms involving a contraction-induced increase in the amount of GLUT4 isoform of the glucose transporter translocating from muscle cytosol to muscle cell membrane.14,2122 Muscle glucose uptake is affected by the size of the total muscle mass engaged in exercise,23 the intensity of the work performed,24 and the length of time the exercise is performed.25 There is a significant negative relationship between muscle glycogen concentration in exercising muscle and glucose uptake in the same exercising muscle.25 A large contracting skeletal muscle like the vastus lateralis can increases its glucose uptake by 11- to 20-fold (from rest) after 40 min of cycling exercise in which the whole body oxygen consumption is about 2–2.3 L/min.2526Therefore, activation of large muscles, such as the quadriceps, can be particularly influential in glucose tolerance. Many exercise programs fail in achieving their objective, i.e., euglycemia, either because large muscle groups were not activated or because the duration and intensity of the exercise routine were too limited.2728

The benefits of activity upon glucose tolerance have historically been outweighed by concerns regarding potential hypoglycemic effects upon the fetus. The insulin resistance that develops in pregnancy leads to higher than normal secretion of insulin to maintain euglycemia, essential for the development of the fetus. Glucose, considered the major metabolic substrate for growth and development of the fetus, is increasingly utilized in the second and third trimesters of pregnancy.29 Hypoglycemia for extended periods of time, or when blood glucose is too tightly controlled, has been demonstrated to have a negative impact on the growth and development of the fetus.30 Maternal fasting and/or starvation are conditions that can challenge the energy reserves, particularly glucose levels. Exercise can similarly challenge maternal glucose reserves with potentially deleterious effects to the fetus. Fasting and exercise lead to an increase in insulin secretion as well as free fatty acid and ketones; when either fasting or exercise is prolonged, there is a decrease in glucose levels.14

Although exercise and fasting share physiologic similarities, they represent different metabolic conditions. One major difference is the release of catecholamines during exercise, a response intended to stimulate gluconeogenesis. The predominant catecholamine released during exercise is norepinephrine, which has a stimulating effect on the uterus. This may result in regular uterine contractions or labor; thus, the recommendation for patients at risk for premature labor is not to engage in physical activity.31 With the exclusion of these women, physical activity does not appear to have detrimental effects.3133Relevant to an exercise protocol for diabetic patients, it was established by us that pregnant women can exercise continuously for 45 min at 55% of aerobic capacity (VO2 max) before potentially experiencing hypoglycemia.32

17.2 Exercise Programs for GDM Treatment

Exercise has been reported as an adjunctive intervention in the management of GDM; however, studies are varied in intensity, frequency, and duration of the exercise prescription. Table 17.1 summarizes exercise studies using various frequencies, intensities, duration, and exercise prescriptions in women with GDM. In these studies, which range from 11 to 96 participants, the exercise intensities range from 50 to 70% of maximum heart rate, which is equivalent to about 40–60% of heart rate reserve (HRR) or about 30–60% of VO2 max.

Table 17.1

Exercise programs for GDM treatment

Study

Subjects

Objective

Methods

Exercise program

Outcome variable

Conclusions

Davenport et al47

n = 20

To determine the effectiveness of a low-intensity walking program on glycemic control and insulin requirements

Case–control study, matched by age, BMI, and insulin, with two controls for every intervention subject in the walking program

Exercise consisted of low-intensity walking (30% heart rate (HR) reserve) 3–4×/week starting at 25 min/sessions, increasing to 40 min/sessions

Exercise subjects experienced a greater average decrease in post exercise blood glucose (BG) of 2.0 mmol/L and required less insulin (0.16 vs. 0.5 units/kg)

A structured low-intensity walking program lowers fasting and postprandial glucose, decreased amounts of insulin, and leads to fewer insulin injections

Artal et al48

n = 96

To determine if weight gain restriction impacts pregnancy outcome in obese women with GDM

Sequential enrollment: subjects were provided a eucaloric diet (15–20 kcal/kg/day) and/or supervised exercise and home-based exercise prescription

60% VO2max walk or stationary bike; supervised (lab) or home exercise 30 min/day 5–6 day/week (or more)

Less weight gain/week in diet only subjects compared to exercise+diet (0.1 vs. 0.3 kg/week; p < 0.05)

Caloric restriction and exercise resulted in lower weight gain with no adverse pregnancy outcomes

Brankston et al34

n = 38

To examine the effects of circuit-type resistance training on insulin requirements in GDM

Subjects were randomized to diet or diet + resistant exercise. Diet consisted of 24–30 kcal/kg/day

Circuit-type resistance exercise of 8 exercises, 15–20 reps, 2–4 sets; increasing weekly for 4 weeks until delivery (average 2.0 sessions/week)

The diet + resistance exercise subjects were prescribed less insulin (0.2 vs. 0.5 units/kg; (p < 0.05) and started insulin later in gestation (1.1 vs. 3.7 weeks; p < 0.05)

Resistance exercise may decrease the need for insulin in GDM pregnancies

Garcia-Patterson, et al49

n = 20

To examine the effects of postprandial exercise on blood glucose after one bout of exercise

Controlled crossover trial on two separate days (3–7 days apart). BG was assessed after one bout of exercise on study day two

Walking on a flat surface, self-paced, for 1-h and seated during the second hour (one bout of exercise)

Significant differences in (control vs. study day) 1-h postprandial BG excursion (1.8 vs. 1.1 mmol/L; p < 0.001)

Light postprandial exercise decreases postprandial BG excursion and may prevent the need for insulin

Avery and Walker38

n = 13

To evaluate the effect of exercise after a session at low and moderate intensity

Repeated measure design to analyze glycemic indices at rest, and after light and moderate intensity exercise

Light intensity at 35% VO2 max; Moderate intensity at 55% VO2 max; 30 min each session

After a single bout of exercise BG levels declined after low to moderate exercise but disappeared after 45 min (p = 0.01)

A dose response to exercise decreases acute BG levels

Avery et al36

n = 33

To determine the effectiveness of a partially home-based, moderate exercise program

Supervised exercise on a cycle ergometer in the lab with a heart rate monitor. Home exercise with perceived exertion scale and self measured heart rate

70% estimated HR max at 30 min. 3–4×/week; 2×/week supervised and 2×/week home based

No differences in fasting or postprandial BG control. Cardiorespiratory fitness increased by 10% in exercise group and 5% in controls (p = 0.005)

A partially-home based exercise program did not reduce BG levels but improved cardiorespiratory fitness

Lesser et al28

n = 11

To examine the effect of one bout of moderate intensity exercise on glycemic excursion following a mixed nutrient meal

Randomized crossover trial to compare BG and insulin levels, with and without exercise 14-h earlier, and following a mixed nutrient meal (600 kcal, 50% carbohydrate, 20% protein, 30% fat)

A single bout of stationary cycling 14-h earlier for 30 min at 60% VO2 max

No differences in glycemic response or plasma insulin levels following a mixed nutrient meal

A single bout of exercise does not improve postprandial glycemic excursion or plasma insulin levels following a mixed nutrient meal

Study

Subjects

Objective

Methods

Exercise program

Outcome variable

Conclusions

Bung et al37

n = 51

To evaluate the beneficial effects of exercise in women with insulin requiring GDM

Subjects with fasting BG between 105 and 130 mg/dL were randomized to exercise + diet or exercise + insulin. Diet consisted of 30 kcal/kg/day.

Recumbent bicycling in lab consisted of 45 min, divided into 3 sessions of 15 min each with 5-min breaks in between at 50% VO2max

No differences in glycemic control in the exercise compared to the insulin group similar outcome date

Exercise and diet can obviate the need for insulin in GDM.

Jovanovic-Peterson et al27

n = 29

To evaluate the impact of exercise using an arm cycle ergometer on glucose tolerance in GDM

Diet consisted of 24–30 kcal/kg/day for 6 weeks. Diet + exercise subjects also participated in 3 exercise sessions/week over 6 weeks

Arm cycle ergometer for 20 min at 70% HR max 3×/week for 6 weeks

Diet+exercise lowered A1C, FBG, and 1-h post prandial glucose

Arm ergometer results in improved glycemic control (glycosylated hemoglobin, fasting BG, and 1-h plasma glucose) compared to diet alone

The most common form of exercise reported was walking or stationary cycling, with studies reporting benefits of resistance training or arm cycle ergometry in decreasing insulin requirements or improving fasting and postprandial glucose excursions.27,34, 37 We demonstrated that pregnant women can exercise more efficiently during nonweight-bearing exercises.35 Nonweight-bearing exercise, such as swimming or stationary cycling, is also better tolerated by physically detrained or sedentary individuals. Jovanovic-Peterson and colleagues published a study which tested the use of arm ergometry as a method for improving glucose tolerance in women with GDM.27Nineteen women with GDM were assigned to either diet or to an arm ergometry exercise program for 6 weeks. Although the subjects assigned to either the mild exercise or diet program achieved a decrease in blood glucose levels, this began to occur after 6 weeks from enrollment into the study. The reason for the modest glucose tolerance response was due to the type and intensity of exercise (i.e., arm ergometry at low intensity for 20 min).

Avery et al randomized 33 women with GDM at less than 34 weeks gestation into an exercise-training program and diet vs. diet alone.36 Those subjects randomized to exercise training were prescribed 30 min sessions of variable exercise, twice weekly both at home and in the laboratory, at 70% of aerobic capacity throughout pregnancy. The exercising subjects completed three bouts of 30 min exercise each week and the control subjects reported 0.7 exercise bouts each week. In contrast to the Jovanovic-Peterson et al study,27 the Avery et al study did not identify significant metabolic effects from exercise. However, the authors observed that the exercise intensity and frequency may not have been sufficient, since half of the exercise sessions were conducted at home and were not supervised.

In another study, Lesser et al enrolled six subjects with GDM into a randomized crossover design study whose objectives were to determine the efficacy of a single cycle ergometry test to affect fasting glycemia, insulin concentration, and insulin excursion following a mixed nutrient meal in a diabetic subject.28 As expected, one single bout of limited exercise (30 min at approximately 60% aerobic capacity) was insufficient to blunt the glycemic response of a mixed nutrient meal; we have observed that it takes an average of 7–10 days for this type of intervention to achieve therapeutic results.

We randomized GDM women to 45 min cycle ergometry exercise at 50% of aerobic capacity, or 5–7.5 times the resting metabolic rate vs. an insulin and diet program.37 The exercise subjects had a compliance rate of more than 90%. The average gestational age at delivery was 39 ± 2 weeks for the insulin group and 38 ± 2 weeks for the exercise group. At eight weeks, no significant differences in glycemic control between the groups were observed; euglycemia was obtained within 1 week and maintained thereafter until delivery. No episodes of hypoglycemia were recorded. Both study groups had similar outcomes, suggesting that an exercise regimen can be offered as a safe and efficient therapeutic option to patients with GDM that require insulin.37

17.3 Physical Activity and GDM Prevention

Table 17.2 summarizes the literature quantifying the amount of exercise necessary to achieve benefit; the majority of these studies focus on GDM prevention and include pre-pregnancy activity levels. Reduced risk of GDM is seen when women exercise the year before pregnancy and during pregnancy. These studies demonstrate that higher exercise intensities are more frequently observed in the year prior to pregnancy with light–moderate activity during pregnancy. The greatest reduction in GDM or in glycemic measures both before and during pregnancy is observed in exercise programs lasting at least several weeks, whereas single bouts of exercise provided the fewest benefits.28,38

Table 17.2

GDM studies using epidemiological data or questionnaires

Epidemiological studies

Study

Subjects

Objective

Methods

Exercise program

Outcome variable

Conclusion

Snapp and Donaldson50

n = 75,160

Assessed the association of maternal exercise during GDM and adverse maternal and infant outcomes

National Maternal Infant Health Survey (NMIHS) to categorize subjects to exercise or nonexercise groups

Reported exercise (leisure time) of at least 30 min, 3×/week or more, for 6 or more months of pregnancy

Exercise subjects were less likely than the nonexercisers to deliver a large for gestational age (LGA) infant

Moderate leisure time physical activity may reduce risk of LGA in women with GDM

Zhang et al40

n = 21,765

Assessed the amount, type, and intensity of pregravid physical activity and association with GDM risk

Nurses’ Health Study II data. Physical activity and sedentary behavior was assessed with a questionnaire

Reported physical activity and sedentary behaviors (such as watching TV)

Total amount of physical activity in MET-hours per week; amount of vigorous physical activity (>6 METS) in MET-hours per week

The amount and intensity of pregravid physical activity was associated with GDM risk. ≥40 MET-hours per week of total physical activity with ≥22.1 MET-hours of vigorous physical activity was associated with the lowest relative risk of GDM (30% less risk)

Dye et al42

n = 12,776

To examine if exercise has a preventative role in decreasing the rate of GDM and if associated with BMI

Data from the Central New York Regional Perinatal Data System (population cohort registry)

Categorized as an exerciser if exercised ≥1×/week for 30 min or more

Lower rates of GDM in those who exercise but only in women with BMI > 33 kg/m2 (OR = 1.9)

Exercise during pregnancy may play a role in reducing the incidence of GDM in obese women

Questionnaires

Oken, et al51

n = 1,896

To determine the association of television viewing and physical activity before and during pregnancy on risk of GDM

Questionnaires to classify activity before and during pregnancy as sedentary, walking, light–moderate, or vigorous and amount of television viewing

Walking (for fun, not at work);

Light–moderate (e.g., bowling, yoga, stretching); Vigorous (e.g., jogging, swimming, cycling, aerobics)

Decreased GDM risk: Vigorous before and none during pregnancy 17%; Vigorous before and light–moderate or vigorous during 51%; no difference in television viewing

Vigorous physical activity before pregnancy and light–moderate physical activity during pregnancy may decrease abnormal glucose tolerance and GDM

Rudra et al41

n = 897

To examine the relationship of perceived exertion 1 year before pregnancy on risk of GDM

Questionnaires –

Seven-Day Physical Activity Recall

Minnesota Leisure-Time Physical Activity

Perceived exertion scale (1–10); Energy expenditure calculated as MET-hours per week: 0.1–14.9, 15.0–29.9, ≥30

Maximal perceived exertion decreased risk of GDM by 81% compared to 43% for minimalexertion

The risk of GDM is inversely related to exercise with maximal perceived exertion providing greater benefits than minimal 1-year prior to pregnancy

Dempsey et al39

n = 909

To examine the relations between recreational physical activity before and during pregnancy on risk of GDM

Interviews to categorize women as inactive or active during pregnancy (using past 7 days) or activity recall 1-year before pregnancy

Energy expenditure was calculated as MET-hours per week from vigorous (e.g., running or aerobics)

Median 21.1 MET-hours per week in the year before pregnancy (56% lower GDM risk) and 28.0 MET-hours per week during pregnancy (74% lower GDM risk)

Women participating in vigorous physical activity before pregnancy and at least light–moderate physical activity during pregnancy were less likely to develop GDM

Dempsey et al examined the relation between recreational physical activity before and during pregnancy and risk of GDM in a prospective cohort study in 900 women using structured questionnaires.39Women who exercised ≥4.2 h/week during the year before pregnancy experienced a 74–76% reduction in risk, even after adjusting for various covariates. Energy expenditure was also associated with a reduced risk of developing GDM such that ≥21.1 MET-hours per week resulted in a 74% risk reduction in GDM.39 Those that spent <21.1 MET-hours per week resulted in a GDM risk reduction of 43%.39MET-hours per week were calculated by dividing the total number of hours spent on each activity per week by the number of weeks during which the activity was performed, multiplying the result by the activity intensity score reported in METS, and summing all reported activities. Pregnant women who exercise ≥28 MET-hours per week had a 30% reduction in the relative risk of GDM. The study also determined that women who exercise before and during pregnancy have as much as a 70% risk reduction in GDM.

Zhang et al40 conducted a prospective cohort study to assess whether the amount, type, and intensity of pregravid physical activity were associated with GDM risk. The analysis included 22,000 women who reported at least one prior singleton pregnancy. Physical activity was assessed with a physical activity questionnaire. Both total and vigorous activity scores were significantly and inversely associated with GDM risk. The relative risks of GDM decreased with total pregravid weekly physical activity such that 16 MET-hours per week showed a 17% reduction in GDM risk and 63 MET-hours per week showed a 30% reduction in GDM risk, compared with those that did not exercise. If the amount of pregravid weekly vigorous physical activity increased (vigorous exercise intensity ≥6 METS or ≥21 mL/kg/min) the relative risk for GDM also decreased, by 20 and 30%, respectively, if 6 and 15 MET-hours per week of vigorous physical activity performed. The inverse associations remained statistically significant after controlling for body mass index (BMI) and other covariates.

Rudra et al showed that those who exercised strenuously up to maximal exertion using the Borg scale of perceived exertion in the year before pregnancy had a 43% decreased in the risk for GDM.41 Women who performed ≥30 MET-hours per week of energy expenditure from physical activity in the year before pregnancy had a 50% decrease in the risk of GDM compared with only a 34% decrease in GDM if the exercise expenditure was less than 14.9 MET-hours per week.41 These findings suggest a potential benefit for the adoption and continuation of an active lifestyle for women of reproductive age that is of vigorous intensity prior to pregnancy.

In 1997, a study we published utilized a population-based birth registry in Central New York State between October 1995 and July 1996.42 Approximately 12,800 women were included in the analysis. When stratified by pre-pregnancy BMI, physical activity was associated with reduced rates of GDM among women with a BMI greater than 33 (odds ratio = 1.9, 95% confidence interval 1.2−3.1) The results of this study suggest that for some obese pregnant women, exercise plays a role in reducing the risk for developing GDM during pregnancy.

17.4 Recommendations for GDM and Activity

Experts agree that pregnancy and postpartum are opportune times for modifying life style43 and risk factors through physical activity and diet.44 Historically, pregnant women and particularly diabetic pregnant women were precluded from engaging in physical activities out of concern for deleterious effects on the fetus. This changed at the Second International Workshop Conference on GDM in 1985. Artal et al and a panel of experts recommended exercise as a therapeutic adjunct in mothers with GDM.45

Currently, exercise is accepted as an adjunct intervention in the management of diabetes in nonpregnant women. The opinion of ACOG is that pregnant patients should continue to exercise in the absence of either other medical or obstetric complications. The ACOG guidelines recommend 30 min or more of moderate exercise/day on most, if not all, days of the week.1 The Society of Obstetricians and Gynecologists of Canada (SOGC) suggest that all women should be encouraged to participate in aerobic and strength conditioning exercise as part of a healthy lifestyle during pregnancy.20

Our recommendations for the management and prevention of GDM are as presented in Table 17.3. Given that moderate exercise intensity is 3–6 METS,46 the maximum number of MET-hours per week expended is 12 MET-hours. Most subjects can engage safely in additional physical activities.

Table 17.3

Artal et al exercise prescription for sedentary, overweight, or obese women with GDM who are unaccustomed to exercise

Previously sedentary, and/or overweight/obese pregnant women

% HRR

% VO2R

RPE

Target exercise energy expenditure (MET-hours per week)

Weeks 1–3 of training (26 weeks gestational age)

35–39

40–45

12–14

≥16

Weeks 3–6 of training (gestational age 29 weeks)

45–55

50–60

13–15

28

Weeks 6–9 of training (gestational age 32 weeks)

60

65

15–16

28

Weeks 9–12 of training (gestational age 35 weeks)

60

65

15–16

28

% HRR = %VO2R unless overweight, sedentary and pregnant. In overweight, sedentary, pregnant women %VO2R is slightly higher by about 5% compared to %HRR until 70% VO2R, after which %VO2R and %HRR are about equal.52 The RPE is rating of perceived exertion from 6 (no exertion) to 20 (maximal exertion)53

%HRR accounts for the measured resting heart rate and the measured maximum heart rate which is based on Karvonen’s method.54 For example, let’s consider an exercise heart rate for a sedentary overweight pregnant woman with GDM: in the beginning of the program, the %HRR should be about 35–39% HRR. If her resting heart rate is 90 beats/min (after sitting upright in a chair for 5 min) and measured maximum heart rate measured from a graded exercise test to volitional exhaustion (VO2 max test) is 185 beats/min, then 39% HRR = 0.39∙(185–90) + 85 = 122 beats/min. Heart rate at maximum exercise should be measured and not estimated as 220 – age because of the large standard deviation of ± beats/min in age predicted maximum heart rate55 and because of the blunted maximum heart rate of 10–15 beats/min that sometime occurs during pregnancy525657

To adhere to the exercise prescription, the pregnant woman should wear a heart rate monitor. If no heart rate monitor is provided, the RPE scale should be followed. Some of the suggested program shown in this table for exercise intensity is based on the ACSM58 and elsewhere.52 The target goal for the amount of physical activity per week expended during pregnancy is based on Dempsey et al (2004)39 which shows a 33% risk reduction in GDM in women who exercise ≥28 MET-hours per week during pregnancy. So for example, one can exercise three METS × 1.6 h/day × 6 days per week = 28.8 MET-hours per week; or one can exercise for less time at a higher intensity to achieve the same expenditure i.e., 5 METS × 0.95 h/day ×6 days per week = 28.5 MET-hours per week. Perceived exertion intensity is a more practical approach.

We recommend that overweight, sedentary pregnant women who have a risk for GDM or have GDM should perform at a minimum level of 16 MET-hours of physical activity, preferably building up to ≥28 MET-hours of physical activity per week. The beginning exercise intensity would be 35–39% of HRR which builds to 60% of HRR at near-term. Any intensity less than 30% HRR and any energy expenditure that is less than 16 MET-hours per week would not be sufficient to bolster fitness benefits or reduce the risk of GDM. Perceived exertion intensity is a more practical approach (of Borg scale 12-14 (out of 20)). In prescribing physical activity to sedentary subjects, it may be more acceptable to discuss a “walking program” than an “exercise program.”

Individualizing an exercise program for women who have GDM involves assessing health and physical fitness, developing a program specific to the patient’s situation, recommending fluid and food intake, and informing the patient about limitations, contraindications, warning signs, and specific concerns. For the purpose of diabetes management and glycemic control, a walking program performed for at least 30 min/day should suffice.

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