Gestational diabetes mellitus (GDM) is one of the most common complications of pregnancy with a prevalence rate varying from 1 to 20 % depending on the population studied and diagnostic criteria applied [48, 49]. Obesity increases the risk of GDM [50, 51]. Indeed, there is evidence that the incidence of GDM may be increasing as the prevalence of obesity among women of reproductive age increases [52–54]. GDM, in turn, increases the risk of subsequent development of diabetes later in life, and this risk is even higher in obese women [55]. Within 15 years of delivery, 70 % of obese women with GDM, compared with 30 % of lean women, will go on to develop type 2 diabetes [56]. GDM is also related to other short- as well as long-term adverse health outcomes for both mothers and their offspring such as maternal hypertensive disorders, cesarean delivery, large-for-gestational-age birth, neonatal hypoglycemia, and neonatal death [57]. In the long term, offspring are at increased risk for obesity, glucose intolerance, and type 2 diabetes [58–60].

Prior observational epidemiologic studies have suggested that prepregnancy physical activity may have a protective role in GDM onset. A meta-analysis found a 55 % lower risk of GDM for women in the highest prepregnancy physical activity quartile compared with those in the lowest quartile (pooled odds ratio [OR] = 0.45, 95 % confidence interval [CI] 0.28–0.75; p = 0.002), as well as a 24 % lower risk of GDM for women in the highest physical activity group during pregnancy compared with those in the lowest physical activity group (pooled OR = 0.76, 95 % CI 0.70–0.83; p < 0.0001) [61].

A recent Cochrane Review comparing the impact of physical activity interventions to usual prenatal care [62] found no significant difference in GDM incidence (three trials, 826 women, risk ratio (RR) 1.10, 95 % confidence interval (CI) 0.66–1.84). In addition, none of the five included trials which evaluated insulin sensitivity found significant differences. Of these studies, two were conducted among obese pregnant women; however, both were small studies and only one evaluated risk of GDM [63, 64]. In the first study, Ong et al. [63] investigated the effect of a supervised 10-week home-based exercise program, beginning at week 18 of gestation, on glucose tolerance and aerobic fitness in 12 previously sedentary obese women. The control arm had reduced glucose tolerance (higher blood glucose levels at 1 and 2 h of the post-intervention oral glucose tolerance test) as compared to the exercise arm, although this was not statistically significant. In the second study, Callaway et al. [64] randomized 50 obese women to an individualized exercise program with an energy expenditure goal of 900 kcal per week (n = 25) or to routine obstetric care (n = 25). While insulin resistance did not differ between the groups, 73 % of women in the intervention group achieved more than 900 kcal/week of exercise-based physical activity at 28 weeks compared with 42 % of women in the control arm. The review concluded that there is limited randomized controlled trial evidence available on the effect of physical activity during pregnancy for preventing pregnancy glucose intolerance or GDM. Larger, well-designed randomized trials, with standardized behavioral interventions, are needed to assess the effects of physical activity on preventing GDM. Seven trials are currently ongoing (see Appendix 9.1) [62].

Hypertensive disorders of pregnancy affect approximately 8 % of pregnancies [65] and include preeclampsia (defined as gestational hypertension with proteinuria) and gestational hypertension (defined as new onset hypertension in pregnancy after 20 weeks’ gestation). Obesity increases the risk of hypertensive disorders of pregnancy [54, 66]. For example, in a large prospective cohort study in Washington State (the Omega Study), Frederick et al. found that every unit increase in prepregnancy BMI resulted in an 8 % increased risk of preeclampsia, with overweight women having almost a twofold increased risk and obese women having over a fourfold increased risk [67]. Consistent with this finding, a significant decrease in risk of hypertensive disorders of pregnancy has been observed when BMI decreases [68]. Hypertensive disorders are the second leading cause of maternal mortality, accounting for 19 % of pregnancy-related deaths for women following a live birth and 20 % of pregnancy-related deaths for women following a still birth [69]. Preeclampsia is associated with an increased risk of preterm delivery, neonatal intensive care unit admission, and fetal death [70].

A recent systematic review [71] found a trend toward a protective effect of PA in the prevention of preeclampsia. Specifically, while six case–control studies found that physical activity had a protective effect on the development of preeclampsia (OR = 0.77, 95 % CI 0.64–0.91), the ten prospective cohort studies found no significant difference (OR = 0.99, 95 % CI 0.93–1.05). The only randomized clinical trial found that the incidence of preeclampsia was 14.6 % (95 % CI, 5.6–29.2) among the walking group and 2.6 % (95 % CI 0.07–13.8) among the stretching group [72].

Because overweight is an established risk factor for preeclampsia, several of these studies evaluated whether physical activity might be particularly beneficial for reduction of preeclampsia risk in this group. In a cohort of 2,793 women in Denmark, Hegaard et al. found that protective effect of recreational physical activity on preeclampsia risk was strongest in overweight women (OR = 0.10, 95 % CI 0.02–1.2), although not significantly so [73]. In contrast, in the Norwegian Mother and Child Cohort Study, Magnus et al. found that the protective effect of exercise was absent among obese women (OR = 1.39, 95 % CI 0.83–2.32), although there was the suggestion of a reduction in risk among overweight women (OR = 0.68, 95 % CI 0.44–1.04) [74, 75]. Rudra et al. found the significant trend of decreased preeclampsia risk with increased perceived exertion was apparent in both overweight and normal weight women [76].

High gestational weight gain (GWG) is independently associated with postpartum weight retention and the long-term development of obesity [77]. Indeed, GWG is the strongest predictor for weight retention [78]. Overweight and obese women are at particular risk for excessive GWG [79]. Because overweight is characterized by insulin resistance and increased systemic inflammatory response [80], it is also associated with increased risk of GDM and preeclampsia [81, 82]. Recent studies also indicate a relationship between high GWG, an abnormal metabolic environment in utero, and increased risk of large-for-gestational-age infants, neonatal death [57], and subsequent childhood adiposity and morbidity [60]. There is observational evidence that physical activity may be a modifiable risk factor for excessive GWG [77]. In observational studies, vigorous physical activity, total physical activity, and walking have been associated with a lower risk of excessive GWG [83–85]. A recent systematic review of randomized controlled trials comparing supervised prenatal exercise intervention with routine standard prenatal care in women who were overweight/obese during pregnancy found that supervised exercise interventions were associated with lower GWG (five trials, n = 216 participants, mean difference of −0.36 kg, 95 % confidence interval −0.64 to −0.09 kg) [86].

Furthermore, a systematic review of lifestyle interventions in overweight/obese pregnant women to improve maternal and perinatal outcomes [51] found that prenatal lifestyle interventions in obese pregnant women reduce maternal pregnancy weight gain (10 RCTs; n = 1,228; −2.21 kg (95 % confidence interval −2.86 kg to −1.59 kg)) although findings were not significant for non-RCTs (six; n = 1,534). Both the successful and non-successful studies included those which were personalized, individual-based, and combined physical activity with dietary guidance. Degrees of weight gain restriction achieved were modest overall, and all the trials were assessed to be of low to medium quality [51]. Future studies are therefore needed to determine the optimal intensity, duration, and type of exercise intervention to reduce excessive GWG among pregnant women overall as well as specifically among overweight/obese pregnant women.

To date, assessment of physical activity during pregnancy and postpartum is predominately conducted via self-report, such as with questionnaires or diaries, rather than with objective measurements, such as accelerometers or pedometers [96]. Several advantages of self-report measures include the lower burden it places on the participant and the reduction in equipment cost as compared to objective assessment of physical activity. Questionnaires can be designed to collect mode of physical activity and perception of intensity. A major disadvantage to both questionnaires and diaries is the potential for recall bias. Moreover, keeping a diary may change the woman’s physical activity behavior, and consistent with this concern, diaries have been used as motivational tools in prior intervention studies. Questions to consider when selecting a self-reported instrument can be found in Table 9.5.

Objective measurement of physical activity is becoming more common among studies of pregnant and postpartum women. Several advantages to objective measures of pregnancy physical activity include the elimination or reduction of literacy, recall bias, and cultural differences. These objective measures (e.g., activity monitors) can also provide a more precise estimation of total physical activity. Disadvantages include cost and dependency on the participant to wear the monitor. The monitors are often worn for up to 1 week and thus do not reflect longer-term patterns of physical activity. They may be inadvertently worn incorrectly if placed at the hip, due to changes in the pregnant woman’s girth [97]. Several studies have noted that compliance to wearing accelerometers declines during pregnancy [98, 99]. This is most likely to occur when participants are instructed to remove the monitor while sleeping, and periods of sleep increase in later pregnancy. Another reason for decline in compliance may be the increasing discomfort associated with wearing the monitor later in pregnancy. To date, the majority of pedometers that have been used in pregnancy only assess locomotion-type activities well (i.e., running, walking) and have not differentiated intensity level. With newer devices, these limitations will likely be overcome.

To date, there has been a critical lack of understanding about overweight/obese women’s beliefs about being active and strategies for overcoming barriers. Several studies not focused among overweight/obese women have documented pregnant women’s PA beliefs during pregnancy, including that PA contributes to overall well-being [100–102], relieves stress [103], reduces anxiety and depressive symptoms [104], helps to control gestational weight gain [101, 104], and manages gestational diabetes [45]. In postpartum, salient physical activity beliefs are that physical activity assists with postpartum weight loss [101, 105], improves mood, and reduces stress [40]. Common barriers to physical activity in pregnancy are increased size, fatigue, and fear of harming the baby [101] and in postpartum are lack of time, companionship support for physical activity, childcare responsibilities, and health issues (e.g., recovering from labor/delivery) [19, 23, 40, 101, 102].

While overweight/obese women may experience many of these same physical activity beliefs and barriers, there is nevertheless little understanding about the unique challenges these women experience with engaging in physical activity before, during, and after pregnancy. One US study by Chang and colleagues [17] found that obese postpartum mothers’ personal experience of physical discomfort (e.g., inability to climb stairs, knee and back pain) and their body size made engaging in physical activity difficult. Another study conducted in the United Kingdom by Weir and colleagues [106] also identified feeling uncomfortable engaging in physical activity due to size (e.g., harder to move when heavier) as well as the perception that physical activity was less important than eating healthy for the baby as salient barriers to prenatal physical activity. Of particular concern, the women in this study were generally unconcerned about weight gain in pregnancy despite the adverse effects of high gestational weight gain on maternal and infant health outcomes. Future research is needed to better understand the physical activity beliefs and barriers of overweight/obese women and the extent to which these psychological factors influence their physical activity attitudes and behaviors and perspectives on gestational weight gain. It is possible that for overweight/obese women, the perceived barriers of physical activity greatly overshadow the benefits, and therefore, there is an important need to identify intervention strategies that effectively reduce barriers and improve their physical activity motivation and behavior.

Although the prenatal physical activity guidelines have been revised on several occasions since the 1985 ACOG recommendations and these adaptations have led to greater support for and promotion of physical activity, there is still a considerable gap in the literature. Specifically, there is an absence of a “gold standard” intervention to promote pre- and postnatal physical activity. A recent systematic review [107] examined interventions to promote physical activity during pregnancy in an effort to identify best practices. Ten intervention studies met the inclusion criteria (i.e., randomized controlled trials measuring efficacy of intervention aiming to change physical activity in pregnant women) of which only two focused on physical activity as the primary target (other targets were gestational weight gain, gestational diabetes, and preeclampsia) and only three reported statistically significant differences between the physical activity intervention and control groups (see Table 9.6). The interventions included a variety of behavioral strategies aiming to promote PA (see Table 9.6); however, none were uniquely associated with positive outcomes. The authors concluded that little is known about the efficacy of interventions for physical activity during pregnancy and offered several suggestions for future research such as designing theoretically based studies to better understand factors influencing physical activity participation, expanding interventions beyond pregnant women to include other important social influences (e.g., family members, social networks, medical providers), and increasing generalizability of evidence to special populations such as ethnic minority groups and overweight and obese pregnant women.