Читать книгу Exercise and Diabetes - Sheri R. Colberg - Страница 9

Chapter 7 Aerobic Exercise Rx for Gestational Diabetes

Gestational diabetes mellitus (GDM), which is maternal hyperglycemia that arises primarily during the third trimester of pregnancy, is usually diagnosed at 24 to 28 weeks of gestation with an oral glucose challenge (American Diabetes Association 2013a, 2013b). Women who have risk factors for gestational diabetes, however, may have this test earlier in the pregnancy. Using new diagnostic criteria, it is estimated that gestational diabetes affects 18% of pregnancies (American Diabetes Association 2013a).

Physical activity performed during pregnancy benefits a woman’s overall health. Instead of detraining, pregnant women undertaking moderate-intensity physical activity can maintain or increase their cardiorespiratory fitness (Ceysens 2006). Furthermore, maternal exercise during pregnancy does not increase the risk of low birth weight, preterm delivery, or early pregnancy loss (Ceysens 2006). On the contrary, regular exercise participation likely reduces the risk of pregnancy complications, such as preeclampsia and GDM, and shortens the duration of active labor (Dyck 2002; Dempsey 2004a, 2004b; Oken 2006; Zhang 2006; Melzer 2010).

Case in Point: Aerobic Exercise Rx for a Woman with GDM

CC is a 32-year-old woman who was recently diagnosed with GDM during week 24 of her pregnancy with a routine oral glucose tolerance test (OGTT). This is her second pregnancy, and although she was not diagnosed with GDM during the first one, her son’s birth weight was >9 lb (9 lb, 2 oz) when she gave birth to him at 39 weeks’ gestation. She considers herself to be a normally active person, getting plenty of daily movement (i.e., standing and walking) at her job as a retail salesperson in a large department store. She has not been doing any planned activities, however, either before or during this pregnancy, although she claims to be active during her leisure time due to continually chasing after her 18-month-old son.

Resting Measurements

Height: 68 inches

Weight: 160 lb (prepregnancy)

BMI: 24.3 (normal)

Heart rate: 80 beats per minute (bpm)

Blood pressure: 118/78 mmHg

Fasting Labs

Plasma glucose: 90 mg/dl (acceptable)

OGTT (75 g of glucose):

1 h: 185 mg/dl (positive diagnosis of GDM)

2 h: 155 mg/dl (positive diagnosis of GDM)

Medications

None currently (although insulin may be initiated if diet and exercise fail to control her blood glucose levels)

Questions to Consider

1. What type of exercise can CC safely start doing at 25 weeks of pregnancy, given her previous sedentary lifestyle?

2. What are an appropriate exercise frequency, intensity, and duration?

3. How should her exercise training progress during the remainder of her pregnancy and after giving birth?

4. What precautions should CC take, and does she have any exercise limitations?

(Continued)

ASSESSING AND TREATING GESTATIONAL DIABETES

GDM has been increasing in prevalence and is associated with a significantly elevated risk of developing type 2 diabetes (T2D) in the next 5–10 years (U.S. Department of Health and Human Services 2011, American Diabetes Association 2013a). Uncontrolled hyperglycemia is potentially harmful to both mother and fetus, resulting in a greater need for cesarian-section deliveries, delivery of larger infants with more excess body fat, a greater risk of infant death and stillborn, and an elevated risk of infant hypoglycemia immediately after birth (Hapo Study Cooperative Research Group 2008, Metzger 2010).

Causes of GDM

The pregnant woman’s placenta supports the fetus as it grows, releasing its own specific hormones that help the fetus to develop, but at the same time blocking the effect of circulating insulin and making the mother more insulin resistant (and, thereby, sparing maternal blood glucose for the growing fetus). Specifically, placental growth hormone induces maternal insulin resistance and mobilizes maternal nutrients for fetal growth, while human placental lactogen and prolactin increase maternal food intake by induction of central leptin resistance and promote maternal β-cell expansion and insulin production to defend against the development of GDM (Newbern 2011). This state of insulin resistance causes the mother’s insulin needs to go up to as much as three or more times normal during the third trimester, resulting in hyperglycemia when the mother’s pancreatic β-cells are unable to keep up with heightened insulin demands. Body fat percentage, physical inactivity, and diet quality are important modifiable risk factors for GDM (Iqbal 2007). These and other important risk factors for GDM are listed in Table 7.1.

Table 7.1 Risk Factors for Development of Gestational Diabetes

Risk for GDM is greatest if a woman:

• Is >25 years old when pregnant

• Has a family history of type 2 diabetes

• Previously gave birth to a baby weighing >9 lb or with a birth defect

• Has high blood pressure

• Has excessive amounts of amniotic fluid

• Has had an unexplained miscarriage or stillbirth

• Was overweight before getting pregnant

• Lives a sedentary lifestyle

Symptoms of GDM

Given its slow onset during pregnancy, GDM usually has no symptoms, or else the symptoms may be mild and not life threatening to the pregnant woman. In most women, blood glucose levels return to normal shortly after delivery.

If symptoms related to hyperglycemia are present, they may include the following:

• Blurred vision

• Fatigue

• Increased thirst

• Increased urination

• Frequent infections (e.g., bladder, vagina, and skin)

• Weight loss despite increased appetite

• Nausea and vomiting

Diagnosis of GDM

Maternal hyperglycemia is most common during the third trimester of pregnancy and is commonly diagnosed with a 75-g OGTT given to all women without prior diabetes at 24–28 weeks of gestation. The OGTT should be administered in the morning to women in a fasted state following an overnight fast of at least 8 h (American Diabetes Association 2013b). The diagnostic criteria are listed in Table 7.2. With the increased prevalence of undiagnosed T2D among women of childbearing age, more women with significant risk factors are being screened for preexisting diabetes at their initial prenatal visit and 6–12 weeks postpartum (American Diabetes Association 2013a, 2013b).

Table 7.2 Diagnostic Criteria for Gestational Diabetes

Fasting Plasma Glucose	1 h OGTT Plasma Glucose	2 h OGTT Plasma Glucose
≥92 mg/dl ≥5.1 mmol/l	≥180 mg/dl ≥10.0 mmol/l	≥153 mg/dl ≥8.5 mmol/l

OGTT, oral glucose tolerance test.

Treatment of GDM

Lifestyle changes. The primary goal of treatment of GDM is to keep blood glucose levels within normal limits throughout the pregnancy to ensure appropriate fetal growth. The first recommendation to achieve this goal is to implement lifestyle changes (i.e., diet and exercise) to manage glycemic control (Committee on Obstetric Practice 2002, Davenport 2008, de Barros 2010, Zavorsky 2011a). A recommended diet for women with GDM is moderate in fat and protein and provides controlled levels of carbohydrates (Artal 2007). Foods to avoid include refined carbohydrates, sugary drinks, fruit juices, pastries, and other sweets that require large amount of insulin to remove excess blood glucose after ingestion. Food intake usually is divided into three small- to moderate-size meals and one or more snacks each day. Pregnant women generally will require no more than 300 extra calories daily to cover their increased energy requirements (Committee on Obstetric Practice 2002).

In addition, pregnant women should be under the care of a health-care provider with whom they can discuss how to adjust amounts of physical activity during pregnancy and the postpartum period. Unless a woman has medical reasons to avoid physical activity during pregnancy, she can begin or continue moderate-intensity aerobic physical activity during her pregnancy and after the baby is born, which should help manage her blood glucose levels (Avery 2001, Brankston 2004, Ceysens 2006, Artal 2007, Iqbal 2007, Chasan-Taber 2008, Davenport 2008, de Barros 2010, Tobias 2011).

Diabetes medications. If lifestyle changes are not successful in maintaining target glucose values during a pregnancy complicated by GDM, glucose-lowering medications may be used (Paglia 2009). Insulin has been the traditional treatment, but the use of oral antidiabetic medications in the management of GDM has increased over the past several years. Both glyburide and metformin (discussed further in chapter 15) have similar pregnancy outcomes compared with insulin (Paglia 2009). Although no substantial maternal or neonatal outcome differences have been found with the use of glyburide or metformin compared with the use of insulin in women with GDM (Nicholson 2009, Dhulkotia 2010), given that both of these oral medications cross the placenta and are available to the fetus, they should be used with caution. Physiological changes associated with regular aerobic training may result in a lowering of the daily medication dose (e.g., insulin or oral agents) needed to manage glucose levels during pregnancy in some women with GDM.

Health outcomes related to uncontrolled GDM. If maternal hyperglycemia is not controlled, the elevated blood glucose levels that are the same in the mother and the developing fetus can lead to macrosomia, or an overly fat baby (usually weighing in excess of 9 lb at birth). Depending on the maternal metabolic and proinflammatory derangements, macrosomia is explained by an excessive availability of nutrients and an increase in fetal insulin release (Vambergue 2011). Macrosomic babies can face health problems of their own, including damage to their shoulders during birth, low blood glucose levels following birth, and breathing problems postdelivery. In addition, babies with excess fat and elevated insulin levels are at higher risk for obesity and T2D themselves. Many women with GDM develop T2D within 5–10 years after delivery, and the risk is increased by excess body weight (U.S. Department of Health and Human Services 2011, American Diabetes Association 2013a). Women with a history of GDM should have lifelong screening for T2D or prediabetes at least every 3 years (American Diabetes Association 2013b).

PREVENTION OF GESTATIONAL DIABETES WITH PHYSICAL ACTIVITY

Women diagnosed with GDM have a substantially greater risk of developing T2D at some point later in their lives. In truth, any degree of abnormal glucose homeostasis in pregnancy independently predicts an increased risk of glucose intolerance postpartum (Retnakaran 2008), and women with either GDM or gestational impaired glucose tolerance exhibit declining β-cell function in the first year after giving birth that likely contributes to their future diabetes risk (Retnakaran 2010).

Physical activity during pregnancy may prevent both GDM and possibly later-onset T2D (Dyck 1998). Engaging in regular physical activity before pregnancy frequently has been associated with a reduced risk of developing GDM (Dyck 2002; Dempsey 2004a, 2004b; Oken 2006; Zhang 2006). Studies testing the effects of such activity during pregnancy have had mixed results, with some studies demonstrating protective effects and other not finding them (Dyck 2002, Dempsey 2004b, Oken 2006). In a recent clinical trial, however, a moderate physical activity program performed thrice weekly during pregnancy was found to improve levels of maternal glucose tolerance in healthy, pregnant women (Barakat 2012) and higher levels of physical activity participation before pregnancy or in early pregnancy significantly lower the risk of developing GDM (Tobias 2011).

Similarly a recent meta-analysis reported that pregnant women with GDM who exercised on a cycle or arm ergometer or performed resistance training three times a week for 20–45 min experienced better glycemic control, lower fasting and postprandial glucose levels, and improved cardiorespiratory fitness (Ceysens 2006). The same number of exercising women ended up being prescribed insulin to control their blood sugars compared with sedentary women, however, and pregnancy outcomes were unchanged.

Recent research has also determined that compared with less vigorous activities, exercise intensity that reaches at least 60% of heart rate reserve (HRR) during pregnancy while gradually increasing physical activity energy expenditure reduces the risk of developing GDM (Zavorsky 2011a). The more vigorous the exercise, the less total exercise time is required. Thus, the general consensus is that higher levels of moderate physical activity (aerobic or resistance training) may reduce the risk of developing GDM during pregnancy and lower blood glucose levels in women who do develop it. Prevention of glucose intolerance during pregnancy may be possible, however, if women of reproductive age engage in leisure time physical activity (particularly vigorous) in advance of becoming pregnant (Retnakaran 2009, Baptiste-Roberts 2011).

EXERCISE PRESCRIPTION FOR WOMEN WITH GESTATIONAL DIABETES

Mode

Most moderate and vigorous aerobic exercise is acceptable during pregnancy with GDM, including both weight-bearing and non–weight-bearing activities like walking, jogging or running, cycling, swimming, water aerobics, aquatic activities, conditioning machines, dancing, chair exercises, and rowing (Committee on Obstetric Practice 2002). During pregnancy, however, women should avoid doing exercises involving lying on their back during the second and third trimesters. They should also avoid activities that increase the risk of falling or abdominal trauma, including contact or collision sports, horseback riding, downhill skiing, water skiing, soccer, and basketball. Late in pregnancy, non–weight-bearing activities may be preferable to weight-bearing activities in some women, especially if low back pain is present (Noon 2012).

In addition, resistance training can be safely and effectively undertaken by pregnant women with GDM and may reduce the number of women who need insulin to control hyperglycemia (de Barros 2010). Low- to moderate-intensity muscle-strengthening exercises performed during the second and third trimesters of pregnancy have a minimal effect on newborn body size and overall health (Zavorsky 2011a, 2011b). Thus, women with GDM can experience greater blood glucose uptake through increased insulin sensitivity from both aerobic and resistance training (Avery 2001, Brankston 2004).

Intensity

For most healthy women who are not already highly active or doing vigorous-intensity activity, moderate-intensity aerobic activity is recommended during pregnancy and the postpartum period, corresponding to 40–59% HRR, “somewhat hard,” or 5–6 on a 10-point rating scale. A more deconditioned woman may start as low as 30% HRR and progress to moderate levels. Women who are already highly active or doing regular vigorous activity (60–89% HRR, “hard,” or a rating of 7–8) can continue these activities during pregnancy.

Because the effects of vigorous-intensity aerobic activity during pregnancy have not been studied carefully, there is no basis for recommending that women should begin such activities during pregnancy if they already were not doing so. Women who habitually engage in vigorous or high amounts of activity or strength training should continue to be physically active during pregnancy and after giving birth; they generally do not need to drastically reduce their activity levels, provided that they remain healthy and discuss with their health-care provider how to adjust activity levels during this time.

Frequency

Pregnant women should engage in physical activity on most, if not all, days of the week. Current guidelines for adults generally recommend five sessions of moderate activity, which would also apply to women with GDM (Haskell 2007, Nelson 2007, Physical Activity Guidelines Advisory Committee 2008). Daily exercise may enhance glucose metabolism further, however, and therefore, the recommended frequency for any type of physical activity for women with GDM is 3–7 days, spread throughout the week.

Duration

Engaging in 30 min of moderate-intensity physical activity on most days of the week, reaching a minimum total of 150 min/week, has been adopted as a recommendation for pregnant women without medical or obstetrical complications (Committee on Obstetric Practice 2002), although studies have shown benefits from daily sessions lasting 20–45 min (Ceysens 2006). Recent research has determined that compared with less vigorous activities, exercise intensity that reaches at least 60% of the HRR during pregnancy while gradually increasing physical-activity energy expenditure reduces the risk of gestational diabetes, and the more vigorous the exercise, the less total exercise time is required. Prolonged-duration physical activity usually is not recommended for pregnant women due to heightened concern over possible hypoglycemia or hyperthermia (Melzer 2010).

Progression

Sedentary and deconditioned women with GDM should start out on the low end of the intensity scale and gradually progress to moderate-intensity exercise (40–59% HRR or higher). Initially, the focus should be on increasing frequency and duration of the exercise rather than intensity. For previously inactive women, moderate-intensity workouts are likely an appropriate endpoint, but if beginning physical activity during pregnancy, women should increase the amount gradually over time. Women who were active before and during pregnancy and before diagnosis of GDM should continue doing moderate- to vigorous-intensity activities (Zavorsky 2011b).

During a normal postpartum period, regular physical activity continues to benefit a woman’s overall health. Moderate-intensity physical activity undertaken after giving birth increases cardiorespiratory fitness and improves mood, with no adverse effects on breast-milk volume, breast-milk composition, or infant growth. An added benefit is that it helps women achieve and maintain a healthy weight postpartum and can promote weight loss when combined with caloric restriction. Pregnant women who habitually engage in vigorous-intensity aerobic activity or are highly active can continue physical activity during pregnancy and the postpartum period, provided that they remain healthy and discuss with their health-care provider how and when activity should be adjusted over time. These recommendations are summarized in Table 7.3.

Table 7.3 Recommended Exercise Rx for Women with Gestational Diabetes

Mode	Aerobic: Walk, stationary cycle, swim, aquatic activities, conditioning machines, prenatal exercise classes, prenatal yoga, seated exercises, and possibly jogging or running (if highly active before pregnancy) Resistance: Light or moderate resistance exercises Exercises to Avoid: Activities lying flat on the back and any that increase the risk of falling or abdominal trauma (e.g., contact or collision sports, horseback riding, downhill skiing, water skiing, soccer, outdoor cycling, basketball, most racquet sports, and scuba diving)
Intensity	If inactive: moderate-intensity aerobic activity (40–59% HRR, or “somewhat hard”) during pregnancy and postpartum If already active or doing vigorous activity: moderate- to vigorous-intensity activity (40–89% HRR, or “somewhat hard” to “hard”)
Frequency	3–7 days, spread throughout the week Better done on most, if not all, days of the week
Duration	30 min/session (range of 20–45 min) At least 150 min of moderate-intensity physical activity spread throughout the week
Progression	If just starting, increase duration of moderate exercise slowly; if already more active, maintain or lower intensity during pregnancy rather than attempting to progress to higher levels

HRR, heart rate reserve.

Case in Point: Wrap-Up

CC plans on working out in the early mornings after dropping her son off at daycare. On her way to work, she can stop at the Y where she is a member and use their exercise equipment and facilities. She enjoys swimming and pool activities, as well as walking on a treadmill and occasionally using some of the aerobic conditioning machines. She thinks that the Y also offers some prenatal exercise classes for pregnant women that she is interested in taking.

Exercise Program Goals

Mode of Activity: Because CC has been mostly sedentary throughout her pregnancy to date (other than daily movement associated with her job), she should start with physical activities that are on the lower end of the intensity scale, such as walking, water aerobics, swimming, stationary cycling, and conditioning machines. She also can consider doing some light resistance training.

Intensity: Given CC’s relative inactivity, she should consider working up to an exercise intensity that feels “somewhat hard” (5–6 on a 10-point scale) and not progress beyond that during the remainder of her pregnancy. Her target heart rate should be around 40–59% HRR (123–144 bpm) to receive maximal glycemic benefits from her training. Initially, she can start out as low as 30% HRR (112 bpm) if higher intensities are too difficult for her to do continuously.

Frequency: Because CC wants to avoid having to go on insulin injections, she is willing to engage in daily exercise during the remainder of her pregnancy, if possible. Her recommended frequency, therefore, is at least 5–7 days/week.

Duration: When starting her programmed exercise, CC should try to do at least 20–30 min of activity daily, with a target goal of a minimum of 150 min of physical activity spread throughout the week.

Progression: CC should progress to doing moderate physical activity, but she should not attempt to do vigorous activities during this pregnancy, given her sedentary lifestyle at the start of training. She can, however, continue with her exercise training after delivery and progress to doing a combination of moderate and vigorous training to lower her risk of developing T2D later in her lifetime.

Daily Movement: If possible, CC should continue to engage in as much daily movement as possible to maximize her energy expenditure (to prevent excess weight gain during pregnancy) and to minimize excursions in her blood glucose levels after eating. She should continue standing and taking steps while working and during her leisure time, whenever possible.

Possible Precautions: Because she is young, CC has limited cardiovascular risk factors. Due to that fact and being pregnant, maximal exercise stress testing is neither necessary nor advisable before starting her exercise program. Because she will not initially be taking insulin or oral medications, her risk of developing hypoglycemia related to exercise is low. She should use a blood glucose monitor to determine the effects of physical activity and dietary changes on her glycemic control.

Women at high risk for GDM may be able to prevent it with lifestyle management during pregnancy. In those who develop GDM, dietary improvements and regular physical activity are frequently sufficient to manage hyperglycemia, although insulin and oral medications may be used when these changes are not enough. Management of blood glucose levels ensures better pregnancy outcomes and improves the health of both the mother and the fetus. Engaging in 30 min of moderate-intensity physical activity on most, if not all, days of the week has been adopted as a recommendation for all pregnant women.

Professional Practice Pearls

• GDM has been increasing in prevalence and is associated with a significantly elevated risk of the woman developing T2D in the next 5–10 years.

• This transient type of diabetes is usually diagnosed in pregnant women at 24 to 28 weeks of gestation using a 75-g oral glucose challenge (OGTT).

• Regular exercise participation during pregnancy likely reduces the risk of pregnancy complications like preeclampsia and shortens the duration of active labor.

• Higher levels of moderate physical activity of any type may reduce the risk of developing GDM during pregnancy and lower blood glucose levels in women who do develop it.

• A state of insulin resistance caused by placental hormone release during the third trimester greatly increases the pregnant woman’s insulin, resulting in hyperglycemia when pancreatic β-cells are unable to keep up with heightened insulin demands.

• Diet and exercise are the first line of treatment for GDM, although insulin and oral medications may be considered if lifestyle changes fail to control blood glucose levels.

• Uncontrolled hyperglycemia is potentially harmful to both mother and fetus, possibly resulting in macrosomic babies and other complications.

• Most moderate and vigorous aerobic exercise is acceptable during pregnancy with GDM, although some forms of exercise that increase risk of falls and traumatic injury should be avoided.

• For most healthy women who are not highly active or doing vigorous-intensity activity, moderate-intensity aerobic activity is recommended during pregnancy and postpartum.

• Women who habitually engage in vigorous or high amounts of activity or strength training can continue these activities during pregnancy and after giving birth.

• Pregnant women should engage in physical activity on most, if not all, days of the week for best glycemic results.

• Engaging in 30 min of moderate intensity physical activity on most days of the week, with a target of ≥150 min weekly, is recommended for women with GDM.

REFERENCES

American Diabetes Association: Diagnosis and classification of diabetes mellitus. Diabetes Care 36 (Suppl. 1):S67–S74, 2013a

American Diabetes Association: Standards of medical care in diabetes—2013. Diabetes Care 36 (Suppl. 1):S11–S66, 2013b

Artal R, Catanzaro RB, Gavard JA, Mostello DJ, Friganza JC: A lifestyle intervention of weight-gain restriction: diet and exercise in obese women with gestational diabetes mellitus. Appl Physiol Nutr Metab 32:596–601, 2007

Avery MD, Walker AJ: Acute effect of exercise on blood glucose and insulin levels in women with gestational diabetes. J Matern Fetal Med 10:52–58, 2001

Baptiste-Roberts K, Ghosh P, Nicholson WK: Pregravid physical activity, dietary intake, and glucose intolerance during pregnancy. J Womens Health (Larchmt) 20:1847–1851, 2011

Barakat R, Cordero Y, Coteron J, Luaces M, Montejo R: Exercise during pregnancy improves maternal glucose screen at 24-28 weeks: a randomised controlled trial. Br J Sports Med 46:656–661, 2012

Brankston GN, Mitchell BF, Ryan EA, Okun NB: Resistance exercise decreases the need for insulin in overweight women with gestational diabetes mellitus. Am J Obstet Gynecol 190:188–193, 2004

Ceysens G, Rouiller D, Boulvain M: Exercise for diabetic pregnant women. Cochrane Database Syst Rev CD004225, 2006

Chasan-Taber L, Schmidt MD, Pekow P, Sternfeld B, Manson JE, Solomon CG, Braun B, and Markenson G: Physical activity and gestational diabetes mellitus among Hispanic women. J Womens Health (Larchmt) 17:999–1008, 2008

Committee on Obstetric Practice: ACOG committee opinion. Exercise during pregnancy and the postpartum period. Number 267, January 2002. American College of Obstetricians and Gynecologists. Int J Gynaecol Obstet 77:79–81, 2002

Davenport MH, Mottola MF, McManus R, Gratton R: A walking intervention improves capillary glucose control in women with gestational diabetes mellitus: a pilot study. Appl Physiol Nutr Metab 33:511–517, 2008

de Barros MC, Lopes MA, Francisco RP, Sapienza AD, Zugaib M: Resistance exercise and glycemic control in women with gestational diabetes mellitus. Am J Obstet Gynecol 203:556.e1–6, 2010

Dempsey JC, Butler CL, Sorensen TK, Lee IM, Thompson ML, Miller RS, Frederick IO, Williams MA: A case-control study of maternal recreational physical activity and risk of gestational diabetes mellitus. Diabetes Res Clin Pract 66:203–215, 2004a

Dempsey JC, Sorensen TK, Williams MA, Lee IM, Miller RS, Dashow EE, Luthy DA: Prospective study of gestational diabetes mellitus risk in relation to maternal recreational physical activity before and during pregnancy. Am J Epidemiol 159:663–670, 2004b

Dhulkotia JS, Ola B, Fraser R, Farrell T: Oral hypoglycemic agents vs insulin in management of gestational diabetes: a systematic review and metaanalysis. Am J Obstet Gynecol 203:457.e1–9, 2010

Dyck R, Klomp H, Tan LK, Turnell RW, Boctor MA: A comparison of rates, risk factors, and outcomes of gestational diabetes between aboriginal and non-aboriginal women in the Saskatoon health district. Diabetes Care 25:487–493, 2002

Dyck RF, Sheppard MS, Cassidy H, Chad K, Tan L, Van Vliet SH: Preventing NIDDM among aboriginal people: is exercise the answer? Description of a pilot project using exercise to prevent gestational diabetes. Int J Circumpolar Health 57 (Suppl. 1):375–378, 1998

Hapo Study Cooperative Research Group, Metzger BE, Lowe LP, Dyer AR, Trimble ER, Chaovarindr U, Coustan DR, Hadden DR, McCance DR, Hod M, McIntyre HD, Oats JJ, Persson B, Rogers MS, Sacks DA: Hyperglycemia and adverse pregnancy outcomes. N Engl J Med 358:1991–2002, 2008

Haskell WL, Lee IM, Pate RR, Powell KE, Blair SN, Franklin BA, Macera CA, Heath GW, Thompson PD, Bauman A: Physical activity and public health: updated recommendation for adults from the American College of Sports Medicine and the American Heart Association. Med Sci Sports Exerc 39:1423–1434, 2007

Iqbal R, Rafique G, Badruddin S, Qureshi R, Cue R, Gray-Donald K: Increased body fat percentage and physical inactivity are independent predictors of gestational diabetes mellitus in South Asian women. Eur J Clin Nutr 61:736–742, 2007

Melzer K, Schutz Y, Boulvain M, Kayser B: Physical activity and pregnancy: cardiovascular adaptations, recommendations and pregnancy outcomes. Sports Med 40:493–507, 2010

Metzger BE, Persson B, Lowe LP, Dyer AR, Cruickshank JK, Deerochanawong C, Halliday HL, Hennis AJ, Liley H, Ng PC, Coustan DR, Hadden DR, Hod M, Oats JJ, Trimble ER, Hapo Study Cooperative Research Group: Hyperglycemia and adverse pregnancy outcome study: neonatal glycemia. Pediatrics 126:e1545–e1552, 2010

Nelson ME, Rejeski WJ, Blair SN, Duncan PW, Judge JO, King AC, Macera CA, Castaneda-Sceppa C: Physical activity and public health in older adults: recommendation from the American College of Sports Medicine and the American Heart Association. Med Sci Sports Exerc 39:1435–1445, 2007

Newbern D, Freemark M: Placental hormones and the control of maternal metabolism and fetal growth. Curr Opin Endocrinol Diabetes Obes 18:409–416, 2011

Nicholson W, Bolen S, Witkop CT, Neale D, Wilson L, Bass E: Benefits and risks of oral diabetes agents compared with insulin in women with gestational diabetes: a systematic review. Obstet Gynecol 113:193–205, 2009

Noon ML, Hoch AZ: Challenges of the pregnant athlete and low back pain. Curr Sports Med Rep 11:43–48, 2012