Hyperglycemia generally refers to the presence of higher than normal glucose levels in the blood (1). In pregnancy, hyperglycemia may be due to chronic conditions such as type 2 diabetes mellitus (T2DM) or prediabetes (PD), or gestational diabetes mellitus (GDM). These three manifestations of hyperglycemia differ in their diagnostic criteria and severity. The United States (U.S.) prevalence of T2DM and PD in women aged 20 years and over has increased by at least two percentage points from 1999-2012, climbing to 13.8% and 35.9%, respectively (2) . The estimated prevalence of GDM in the U.S., based on data from the 2007-2014 National Health and Nutrition Examination Survey (NHANES) is 7.6%(3).
A T2DM diagnosis can be confirmed by: fasting plasma glucose (PG) ≥7 mmol/L, a two-hour (2-H) PG ≥11.1 mmol/L after a 75 g glucose load during oral glucose tolerance test (OGTT), or a glycohemoglobin (A1C) ≥6.5%(4). Accurate diagnosis requires at least two separate positive readings for the same test. In addition, one instance of classic symptoms of hyperglycemic crisis with a random PG ≥11.1 mmol/L may confirm diagnosis. Type 2 diabetes diagnosis heightens the risk for blindness, kidney failure, lower limb amputations, cardiovascular events, and complications in pregnancy(5). Type 2 diabetes has also been shown to augment risk for cardiovascular diseases (CVD)(6).
Prediabetes diagnosis is like that of T2DM, modified with lower cut points: fasting PG 5.6-6.9 mmol/L, 2-H OGTT 7.8-11.0 mmol/L after a 75g glucose load, and A1C 5.7-6.4%(1). Not unlike T2DM, PD carries a risk of damage to the eyes, kidneys, blood vessels, and heart (7). Furthermore, 5-10% of patients with PD progress to T2DM annually(8). In order to prevent disease progression, first line treatment includes: weight loss of 5-10% of body weight and 30 minutes a day of moderate intensity physical activity (PA).
Gestational diabetes initiates in pregnancy and resolves after delivery (2). Diagnosis is often based on a 3-H 100g OGTT. Diagnosis is confirmed by two or more of: a fasting PG 5.3-6.9 mmol/L, 1-H PG ≥10.0 mmol/L, a 2-H PG 8.6-11.0 mmol/L, and a 3-H PG 7.8-11.0 mmol/L (9). However, screening methods and diagnostic criteria have varied across years and governing bodies (10). This has led to varying prevalence estimates and uncertainty for patients who may not have received GDM diagnosis in previous years(11). Although GDM is not a lifelong disease, it is associated with over a seven-fold risk for T2DM (12) and a 50% increased risk for CVD(13). Maternal and fetal sequelae of GDM include increased perinatal mortality, fetal macrosomia, neonatal hypoglycemia, cesarean section, and postpartum depression (14). Furthermore, glucose intolerance, T2DM, and obesity risk are heightened in GDM offspring(15).
Physical activity has been shown to restore insulin sensitivity and minimize impaired glucose tolerance in pregnancy (16). A meta-analysis of 40 observational studies reported a 30% reduction in GDM risk for any general amount of PA(17). Further evidence of the benefits of PA comes from a 2020 meta-analysis by Doi et al, which reported a 30% GDM risk reduction as the overall effect of 11 PA interventions in pregnancy (18). Exercise can positively impact fetal body composition with an overall increase in fetal weight and decrease in percent of fetal mass. This is due to improved maternal glucose control, improved maternal autonomic control, improved placental oxidative stress, and placental efficiency(19).
In 2008, the Department of Health and Human Services (DHHS) provided PA recommendations for the health and well-being of American citizens, pregnant women included, with new, revised recommendations released in 2018 (20). The new 2018 PA Guidelines for adults are comparable to the previous guidelines modified to allow AA bout duration minimums of 2 minutes (21). Although national guidelines have been established, clinical advice on PA may differ across the U.S., depending on the personal views, time constraints, training, and confidence in dissemination of PA recommendations (22, 23).
Due to their unique medical considerations, pregnant women have separate recommendations for PA. Current recommendations made by the American College of Obstetricians and Gynecologists (ACOG) in 2020 state that exercise and/or PA is beneficial for most pregnant women but modifications in exercises may be necessary to account for physiological and anatomical changes (24). Pregnant women should be thoroughly evaluated by an obstetrician-gynecologist before PA recommendations are made to ensure the patient does not have medical contraindications. Women with uncomplicated pregnancies should be encouraged to engage in aerobic and muscle strengthening activities (MSA) before, during, and after pregnancy. Furthermore, activity restriction should not be routinely prescribed as a treatment to reduce preterm birth. Indeed, sedentary behavior has shown to be associated with increased risk of GDM despite high PA levels, and particularly in women with excessive gestational weight gain (25).
The 2008 and more recent 2018 U.S. DHHS guidelines on PA in pregnancy recommend at least 150 minutes of moderate-intensity AA per week, avoiding supine position and high fall risk sports such as horseback riding (20, 21). Similarly, the 2019 Canadian guidelines recommend 150 minutes of moderate-intensity aerobic activity (AA) per week, a minimum of three days per week (26). Reinforcement of the importance of these recommendations comes from a recent umbrella review which found strong evidence that moderate-intensity PA reduced the risk of GDM, symptoms of postpartum depression, and excessive gestational weight gain (27).
In addition, Canadian guidelines encourage incorporation of a variety of aerobic and resistance exercise in addition to yoga, stretching, and pelvic floor muscle training. Limited evidence exists on ideal dose of MSA for pregnant women (28). However, as previously mentioned, resistance exercise is encouraged in both Canadian and ACOG guidelines (24, 26).
Despite the overwhelming evidence of benefits (29), less than 15% of women achieve the minimum recommendation of 150 minutes of moderate intensity PA per week during pregnancy (30). About one third of pregnant women do not engage in any PA (31). Understanding the various characteristics and behaviors which may contribute to PA engagement or lack thereof is necessary to inform effective interventions. Such factors include proxies for social determinants of health such as race/ethnicity and education level, characteristics such as age and number of children (32-35), and behaviors such as smoking and pre-pregnancy PA levels (34, 35).
Though we know that PA recommendations in pregnancy are infrequently met, sparse information exists on how self-reported GDM and PD histories compare with self-reported diabetes and euglycemia in meeting AA recommendations and two days of MSA per week. This study will examine the differences in PA engagement for parous women with varied diabetes risk status (DRS). Therefore, the study aims to answer three questions: 1) Is there an association between DRS and meeting the 2008 DHHS PA recommendation in pregnancy? 2) Is there an association between DRS and engaging in at least two days of MSA per week in pregnancy? 3) Are there other major characteristics that are associated with meeting the AA recommendations and two days of MSA in pregnancy?