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      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

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