Physical activity reduces risk of type 2 diabetes after gestational diabetes
Date posted: August 14, 2014
Increasing evidence suggests that an active lifestyle reduces the risk of developing type 2 diabetes in women with gestational diabetes. In a 16-year prospective observational study, 14 percent of women with a history of gestational diabetes self-reported the development of type 2 diabetes . Women with a total physical activity level equivalent to 150 minutes per week of moderate-intensity physical activity or 75 minutes per week of vigorous-intensity physical activity had a 30 to 50 percent lower risk of developing type 2 diabetes than women with lower levels of physical activity.
Follow-up and prevention of type 2 diabetes — ACOG, the ADA and the Fifth International Workshop Conference on Gestational Diabetes recommend long-term follow-up of women with GDM.
All women with previous GDM should undergo an oral glucose tolerance test 6 to 12 weeks after delivery, using a two-hour 75 gram oral glucose tolerance test. Breastfeeding during the test appears to have a modest effect on glucose levels. In a prospective cohort study of nursing women with previous GDM who underwent a glucose tolerance test 6 to 9 weeks postpartum, mean two-hour glucose levels were 5 percent lower in women who breastfed during the test, which could affect interpretation of a borderline test. The patient should be informed in advance that she might need to repeat the test if this happens so she can make an informed decision about breastfeeding during the test versus planning the test at a time/later date when breastfeeding can be avoided.
An abnormal fasting plasma glucose level is diagnostic (diabetes if ≥126 mg/dL, impaired fasting glucose (IFG) if 100 to 125 mg/dL); however, sensitivity for diagnosis of diabetes is low compared with glucose tolerance tests. Impaired glucose tolerance (IGT) is diagnosed if the two-hour value is 140 to 199 mg/dL. Collectively, IFG and IGT are known as “prediabetes.”
- Women with an abnormal oral glucose tolerance test are then classified as having prediabetes or overt diabetes mellitus.
- Those with prediabetes should be counseled about their subsequent risk for developing overt diabetes and referred for discussion of management options (eg, lifestyle modification such as medical nutritional therapy, indications for metformin). They should try to achieve their ideal body weight through diet and exercise and, if possible, they should avoid drugs that may adversely affect glucose tolerance (eg, glucocorticoids). They should have yearly assessment of glycemic status.
- A woman who has overt diabetes mellitus should receive appropriate education and treatment. She should also be given advice regarding contraception and the planning of future pregnancies.
- Women with prediabetes or overt diabetes should be counseled regarding the importance of good metabolic control prior to any future pregnancies.
- Women with normal glucose tolerance should be counseled regarding their risk of developing GDM in subsequent pregnancies and their future risk of developing type 2 diabetes. Lifestyle interventions (weight loss, exercise) are clearly beneficial for reducing the incidence of these disorders. In a randomized trial comparing use of metformin versus lifestyle intervention and placebo in 350 women with previous GDM, the annual incidence of type 2 diabetes was decreased from 15 to 7.5 percent with either intervention. The number needed to treat to prevent one case of diabetes over three years was 5 to 6. In a subgroup analysis of former GDMs enrolled in a 16-year prospective observational study (Nurses Health Study II), 14 percent self-reported the development of type 2 diabetes. Women with a total physical activity level equivalent to 150 minutes per week of moderate-intensity physical activity or 75 minutes per week of vigorous-intensity physical activity had a 30 to 50 percent lower risk of developing type 2 diabetes compared with women who did not achieve this level of activity, which is the minimum recommended for United States adults in federal physical activity guidelines. BMI at baseline was inversely associated with activity level and adjustment for BMI attenuated the effect of physical activity, although the benefit of physical activity remained statistically significant.
Drug therapy (eg, metformin, pioglitazone) also may have a role in preventing future type 2 diabetes. In a multicenter randomized trial, both intensive lifestyle and metformin therapy reduced the incidence of future diabetes by approximately 50 percent compared to placebo in women with a history of GDM; metformin was much less effective than lifestyle intervention in parous women without previous GDM . This topic is discussed in detail separately.
Long-term follow-up is essential. Reassessment of glycemic status should be undertaken at a minimum of every three years, but the best means of follow-up has not been defined. More frequent assessment may be important in women who may become pregnant again, since early detection of diabetes is important to preconception and early prenatal care. The 75-g oral two-hour glucose tolerance test is the more sensitive test for diagnosis of diabetes and impaired glucose tolerance in most populations, but the fasting plasma glucose is more convenient, specific, and reproducible, and less expensive. Glycated hemoglobin (A1C) is convenient and the preferred test for patients who have not fasted overnight.
In women who did not undergo screening for GDM, but diabetes is suspected postpartum because of infant outcome, postpartum glucose tolerance testing may be considered. However, a negative postpartum GTT only excludes the presence of type 1 or type 2 diabetes or prediabetes at the time of the test; it does not exclude the possibility that glucose impairment was present in association with the metabolic changes occurring during the pregnancy itself. Indications for screening and screening tests are discussed separately.
2. Bao W, Tobias DK, Bowers K, et al. Physical activity and sedentary behaviors associated with risk of progression from gestational diabetes mellitus to type 2 diabetes mellitus: a prospective cohort study. JAMA Intern Med 2014; 174:1047.