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