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