Gestational Diabetes

Abstract

Gestational diabetes mellitus (GDM) is one of the most common complications of pregnancy and is strongly related to subsequent risk of type 2 diabetes. The epidemics of obesity and diabetes and the increasing incidence of GDM in recent years highlight the importance of preventing GDM among women at high risk to avoid the associated short- and long-term adverse health outcomes for both mothers and their offspring. Indeed, women may be more likely to adopt healthy lifestyle habits during pregnancy and maintain these habits into the postpartum period. Although there is substantial evidence that targeting at-risk groups for type 2 diabetes prevention is effective if lifestyle changes are made, relatively little attention has been paid to the prevention of GDM. Therefore, the objective of this article is to review the scientific evidence regarding the association between modifiable risk factors and GDM; discuss how lifestyle interventions, including weight management through diet and exercise could be successful in reducing the risk for GDM; and provide recommendations for future lifestyle intervention programs with a focus on translation and dissemination of research findings.

Introduction

Type 2 diabetes is a global epidemic affecting approximately 21 million people in the United States. ¹ The age at onset for type 2 diabetes has decreased, ¹ highlighting the importance of identifying high-risk groups early in order to implement strategies to delay or prevent diabetes onset. One such high-risk group is women who develop gestational diabetes mellitus (GDM) or milder forms of glucose intolerance in pregnancy.^2,3 Indeed, a recent meta-analysis found that GDM confers a 7-fold risk for future type 2 diabetes, ⁴ and up to one third of women with type 2 diabetes have previously been diagnosed with GDM.^2,5

In other words, GDM unveils a preexisting susceptibility for type 2 diabetes and provides an excellent opportunity to implement interventions to prevent or delay the development of this disorder.

According to a recent systematic review, the highest risk period for the development of type 2 diabetes is within the first 5 years after a GDM pregnancy, ² with, for example, 50% of Hispanic women developing type 2 diabetes within 5 years. ⁶ This is consistent with recent findings showing a rapid postpartum change in glucose tolerance; by 12 months postpartum, 17.1% of those with recent GDM and 10% of women with milder degrees of gestational glucose intolerance had progressed to prediabetes or diabetes. ⁷ In other words, GDM unveils a preexisting susceptibility for type 2 diabetes and provides an excellent opportunity to implement interventions to prevent or delay the development of this disorder.

GDM is one of the most common complications of pregnancy. The prevalence of GDM is between 1% and 14%, and on average, approximately 4% of all pregnancies are complicated by GDM, resulting in more than 200 000 cases annually in the United States. ⁸ There is evidence that the incidence of GDM and of postpartum type 2 diabetes following a diagnosis of GDM may both be increasing as the prevalence of obesity among women of reproductive age increases.^5,9,10

In addition to its impact on type 2 diabetes, GDM is related to short-term and other long-term adverse health outcomes for both mothers and their offspring. Women with GDM are at increased risk of maternal hypertensive disorders and cesarean delivery and are also more likely to display features of the insulin resistance syndrome that are linked to cardiovascular disease. ⁸ In the short term, offspring of women with GDM are at increased risk for being large for gestational age, neonatal hypoglycemia, and fetal and neonatal death. ¹¹ In the long term, children are at increased risk for obesity, glucose intolerance, and type 2 diabetes themselves.^8,12,13

In light of the increasing prevalence of GDM and its associated risk factors and sequelae, the need for strategies to target modifiable risk factors that may prevent GDM becomes critical. There is substantial evidence that targeting at-risk groups for type 2 diabetes prevention is effective if lifestyle changes are made. For example, the Diabetes Prevention Program (DPP) found that intensive lifestyle modification over 4 years with diet and exercise reduced the incidence of type 2 diabetes by more than 50%. ¹⁴ However, lifestyle interventions designed to prevent the incidence of GDM are sparse.

Therefore, the objective of this article is to review the scientific evidence regarding the association between modifiable risk factors and GDM, discuss how lifestyle interventions, including weight management through diet and exercise, could be successful in reducing the risk for GDM, and provide recommendations for future lifestyle intervention programs with a focus on translation and dissemination of research findings.

At-Risk Populations

Certain subgroups of women are at greater risk for GDM. Established GDM risk factors include increased maternal age, ethnicity (eg, Aboriginal, Hispanic, south Asian, Asian, or African descent), diabetes in a first-degree relative, previous macrosomic infant, personal history of abnormal glucose tolerance, and excess adiposity before pregnancy.^15,16 For example, studies have shown that 60% to 80% of women with GDM are obese and that risk significantly and progressively increases across BMI categories of overweight, obese, and morbidly obese.^17,18 Recent studies also suggest that individual components of pregravid cardiometabolic risk profile, such as mild hyperglycemia and prehypertension/hypertension, may be associated with GDM risk. ¹⁹ Other potential risk factors that have been considered are multiple pregnancies, polycystic ovarian disease, and short maternal stature, although findings have not been consistent. ¹⁸

Modifiable Risk Factors for GDM: Evidence from Observational Studies

Physical Activity

Prior observational epidemiological studies have suggested that prepregnancy physical activity may have a protective role in the development of GDM.^20-25 A recent meta-analysis indicated a 55% lower risk of GDM for women in the highest prepregnancy physical activity quantile compared with those in the lowest quantile (pooled odds ratio [OR] = 0.45; 95% confidence interval [CI] = 0.28-0.75; P = .002). ²⁶ Studies examining activity during pregnancy have found similar results, albeit somewhat less consistently, with several studies^24,27 observing a significant protective effect and others supporting this trend but not significantly so.^21,22,28 The same meta-analysis indicated a 24% lower risk of GDM for women in the highest activity group during pregnancy compared with those in the lowest activity group (pooled OR = 0.76; 95% CI = 0.70-0.83; P < .0001). ²⁶

In light of the fact that walking is the most popular form of exercise in pregnancy, ²⁹ several of these observational studies evaluated the impact of walking independently.^22,23,27 Studies were consistent in finding that increased intensity of walking pace was significantly and inversely associated with GDM risk, although it was unclear whether walking duration (distance or time) had a similar protective effect. For example, women who reported a brisk usual walking pace and longer durations of walking prior to pregnancy had a reduced risk of GDM compared with women reporting a casual usual pace and shorter durations of walking (pooled OR = 0.59; 95% CI = 0.30-0.87). ²⁶ However, this association was attenuated and no longer statistically significant in early pregnancy.

Few studies have addressed the association between an inactive lifestyle before or in early pregnancy and risk of GDM. In general, these studies have been suggestive but failed to show statistically significant associations between sedentary behavior, as well as hours watching television, and GDM risk.^22,23,30 However, the hypothesis that sedentary behavior may reduce the risk of GDM is supported by strong evidence in nonpregnant women.^31-33 A recent meta-analysis found that greater TV viewing time was associated with a higher risk of type 2 diabetes (pooled relative risk [RR] = 1.20; 95% CI = 1.14-1.27 per 2 hours of TV viewing time), and a linear dose–response relationship was observed. ³¹

In summary, data from observational epidemiological studies suggest that both prepregnancy and early pregnancy physical activity are important risk factors for GDM and that the protective effect appears to increase with intensity and time spent on physical activity, including common activities such as walking.

Dietary Factors

Observational epidemiological studies of the association between dietary factors and risk of GDM are relatively sparse. Early studies suggested that midpregnancy macronutrients, such as higher intake of saturated fat and lower intake of polyunsaturated fat, were associated with increased incidence or recurrence of GDM, but these results were not consistent.^34-37 These studies were also often limited by cross-sectional or retrospective designs, failed to adjust for other components of the diet, and could not determine whether dietary composition was more important than prepregnancy BMI in terms of GDM risk. ³⁸ More recent prospective studies that considered the correlation between nutrients suggested that higher intake of fat and lower intake of carbohydrates may be associated with increased risk of GDM independent of prepregnancy BMI^36,38 but not consistently so. ¹⁵

Findings for fiber have also been inconsistent, with some studies supporting a protective effect,^39,40 whereas others have not.^15,34,35 High cholesterol intakes both before and during pregnancy have been associated with increased risk of GDM. ⁴¹ Glycemic load prior to pregnancy was associated with increased risk of GDM in a large, prospective cohort of 21 765 nurses, ²³ but glycemic load during early pregnancy was not associated with GDM risk in a cohort of 1733 women enrolled in Project Viva. ¹⁵

Observational studies have not demonstrated a relationship between total energy intake (kcal) and risk of GDM.^{15,34,35,42,43} However, as with all studies relying on self-reported data, lack of statistically significant findings may be partly a result of error in reporting caloric intake (eg, underreporting).

In terms of micronutrients, lower plasma vitamin C ⁴⁴ and vitamin D ⁴⁵ in early pregnancy have been significantly associated with increased GDM risk. Some studies have shown that dietary intake of certain types of foods may also influence GDM risk, such as sugar-sweetened cola and eggs, but evidence is sparse.^41,46 Most recently, prepregnancy dietary patterns have been associated with GDM risk, with strong positive associations observed for a Western dietary pattern (ie, high intake of red meat, processed meat, refined grain products, sweets, French fries, and pizza) as compared with a prudent dietary pattern, even after adjustment for established GDM risk factors. ⁴⁷ This may be explained, in part, by recent findings that higher maternal dietary iron intake (eg, reflected in higher consumption of red meat) is associated with GDM.^48,49

In summary, observational epidemiological studies of dietary factors and risk of GDM are somewhat sparse and inconsistent but support the theory that dietary factors may play a role. Overall, evidence appears to be strongest for pregravid dietary patterns (eg, Western) as well as higher dietary fat intake and lower carbohydrate intake during pregnancy in terms of increasing GDM risk.

Gestational Weight Gain

Recent studies suggest that excessive gestational weight gain may be associated with increased risk of GDM as well as milder forms of abnormal glucose tolerance, particularly in overweight and obese women. Gestational weight gain in early pregnancy may have the strongest impact on risk.^50-56

Gestational weight gain may be on a causal pathway between lifestyle behaviors such as physical activity and diet and subsequent GDM risk. Limited data are available, however, on the role of physical activity and diet as modifiable predictors of excessive gestational weight gain. A recent review of observational epidemiological studies found positive significant associations between total energy intake and gestational weight gain, although not consistently so. ⁵⁷ Further significant positive associations were observed between protein intake, animal lipids, energy-dense foods, and number of different food servings per day and increased gestational weight gain, whereas inverse associations were observed for carbohydrate intake and a vegetarian diet. ⁵⁷ In terms of specific food items, consumption of fruits and vegetables, whole grains, and fiber have not been independently associated with gestational weight gain, whereas in 1 study, greater sugar-sweetened beverage intake was associated with lower total gestational weight gain. ⁵⁸

Overall, evidence appears to be strongest for the association between lower total calories and carbohydrates and reduced gestational weight gain.

There is also evidence that physical activity may be a modifiable risk factor for gestational weight gain. Vigorous activity during pregnancy, as well as walking and total activity, has been associated with a lower risk of excessive gestational weight gain, whereas women who were less physically active during pregnancy than prior to pregnancy were more likely to exceed IOM guidelines for gestational weight gain.^58-60

These findings suggest that targeting healthy eating and modest physical activity during pregnancy may help improve compliance with gestational weight gain guidelines and, in turn, reduce the risk of GDM. ⁶¹ Further studies are needed to explore the effect of dietary factors, particularly macronutrient intake, on gestational weight gain.

Cigarette Smoking

Smoking has been associated with increased insulin resistance and type 2 diabetes in nonpregnant women. ⁶² However, epidemiological evidence supporting the role of smoking as a risk factor for GDM is limited, and there is significant heterogeneity in research design. ⁶³ With few exceptions, the majority of studies have examined smoking as a dichotomous variable, and many did not adjust for important confounding factors. In a review article, Wendland et al ⁶³ obtained an adjusted OR of 0.95 (95% CI = 0.85-1.07) for smoking during pregnancy and risk of GDM. Some studies, however, suggest that prepregnancy smoking may be associated with increased risk.^64,65 Among 14 613 participants in the Nurses Health Study, Solomon et al ⁶⁴ found that, compared with nonsmokers, pregravid smokers of 5+ cigarettes per day had an increased risk of GDM (RR = 1.65; 95% CI = 1.05-2.58) compared with pregravid nonsmokers. It is possible, however, that observed increased risks among prepregnancy smokers may be a result of the effect of quitting smoking. Quitting or reducing the number of cigarettes smoked during pregnancy may lead to increased gestational weight gain, ⁶⁶ a risk factor for GDM. ⁶⁷

Intervention Studies Designed to Prevent or Reduce the Risk of GDM

Few primary prevention studies have intervened to test whether making a change in lifestyle factors such as physical activity, diet, and gestational weight gain can prevent GDM among women at high risk of this disorder. As described below, with few exceptions, current lifestyle intervention studies largely reflect pilot studies or recently initiated trials.

Lifestyle Intervention Trials

Recently, Luoto et al ⁶⁸ conducted a cluster-randomized trial among 399 women with at least 1 GDM risk factor in any earlier pregnancy in 14 municipalities in Finland. Women were randomized to a lifestyle intervention consisting of individual counseling on physical activity, diet, and weight gain at 5 antenatal visits or to usual care. The aims of the physical activity counseling were to increase leisure time activity to the recommended levels (800 MET [metabolic equivalent] min/wk). ⁶⁹ The goal of the dietary counseling was to help participants achieve a healthy diet containing <10% saturated fat, 5% to 10% polyunsaturated fat, 25% to 30% total fat, and <10% saccharose of total energy intake and 25 to 35 g/d of fiber. There was no significant difference in GDM incidence between study arms, with 15.8% (34/216) of women in the intervention group and 12.4% (22/179) of women in the usual care group developing GDM (RR = 1.36; 95% CI = 0.71-2.62). However, there was some indication that the intervention led to positive changes in diet and physical activity. For example, women in the intervention group increased their intake of dietary fiber and polyunsaturated fatty acids and decreased their intake of saturated fatty acids and saccharose. The intervention arm also had the suggestion of a smaller decrease in at least moderate-intensity activity (91 MET min/wk; 95% CI = −37-219) than women in the usual care group. The authors conducted a subgroup analysis among women in the intervention group who fulfilled at least 4 of the 5 dietary aims, whose physical activity exceeded 800 MET min/wk at 36 to 37 weeks gestation, or whose total weight gain did not exceed BMI-specific limits as recommended by the 1990 Institute of Medicine (IOM) Report ⁷⁰ (“adherent” women; 24% or 55/229). As compared with women in the usual care group, adherent women had the suggestion of a lower risk of GDM (27.3% vs 33.0%; P = .43). This study was limited, in part, by the relatively small number of cases and the resulting reduced statistical power.

In another recent study, Quinlivan et al ⁷¹ randomized 124 obese pregnant women in Australia to a 4-step multidisciplinary prenatal care program or to standard obstetric care. The intervention consisted of (1) continuity of provider; (2) weighing at each visit; (3) brief (5-minute) dietary counseling and education, including itemization of the food consumption of the previous day with a focus on reducing consumption of fast foods, sports drinks, carbonated drinks, commercial fruit juices and increasing fruit and vegetables; and (4) a clinical psychology assessment of symptoms of depression, anxiety, stress, and their relationship with eating patterns. As compared with the standard obstetric care group, women randomized to the intervention group had a significant reduction in the incidence of GDM (OR = 0.17; 95% CI = 0.03-0.95) and reduced weight gain in pregnancy (7 vs 13.8 kg; P < .0001), although the number of cases was small (4 vs 17).

Diet-Only Intervention Trials

The Cochrane Review reviewed randomized and quasi-randomized (ie, allocation based on alternation, date of birth, or case record number) controlled trials of dietary strategies designed to prevent GDM in pregnant women. ⁷² One study assessed the effect of a high-fiber diet ⁷³ and 2 studies compared the impact of high- and low-glycemic index diets.^74,75 Glycemic index is a numerical index given to a carbohydrate-rich food that is based on the average increase in blood glucose levels occurring after the food is eaten; the higher the index, the greater the blood glucose response. ⁷⁶ In the first, Fraser ⁷³ randomized 23 nonobese women at 27 weeks gestation to a high-fiber diet group or a control group. The high-fiber group received advice from a dietitian to reduce their intake of sucrose and white flour and to make as many high-fiber substitutions as possible. The control group was given standard dietary advice. There was no significant difference in mean oral glucose tolerance test results at 35 weeks between the groups (mean difference = −0.36; 95% CI = −0.90-0.18). However, there was a significant attenuation of postprandial insulin secretion in the high-fiber group.

Moses et al ⁷⁵ and Clapp et al ⁷⁴ randomly assigned a small number of women (ranging from n = 20 to n = 62) to either a low- or high-glycemic index ⁷⁶ diet in early pregnancy. The 1 study to assess GDM as an outcome observed only 1 case in the high-glycemic index group and none in the low-glycemic index group. ⁷⁵ For both studies, maternal fasting blood glucose was lower on the low-glycemic index diet (weighted mean difference = −0.28 mmol/L; 95% CI = 0.54 to −0.02) as compared with the value for the high-glycemic index diet.

Lifestyle Intervention Trials Targeting Gestational Weight Gain

Gestational weight gain is an important risk factor for GDM suggesting that intervening on weight gain may, in turn, lead to a reduction in GDM risk. Several randomized and nonrandomized controlled trials have been designed to reduce excessive gestational weight gain.^77-89 The majority of trials, however, demonstrated minimal effectiveness and were limited to small samples of predominantly non- Hispanic white women, lacked behavioral strategies for dietary and physical activity change, or relied on historical control groups.^90,91

The content of the intervention in the majority of these trials was dietetic counseling alone; however, those trials that included exercise in addition to diet were more likely to observe the suggestion of a protective effect. A meta-analysis of trials with physical activity as the intervention, found a significant reduction in gestational weight gain in the intervention group as compared with the control group (−0.61 kg; 95% CI = −1.17 to −0.06). ⁹²

For example, in one of the largest studies conducted to date, Phelan et al ⁸³ randomized 401 pregnant women to a low-intensity behavioral intervention or to standard care. The intervention included 1 face-to-face visit; weekly mailed materials that promoted an appropriate weight gain, healthy eating, and exercise; individual graphs of weight gain; and telephone-based feedback. Normal-weight women in the intervention arm were less likely to exceed IOM recommendations for gestational weight gain as compared with women in the standard care group (40.2% vs 52.1%, P = .003); however, the intervention did not have a significant impact on gestational weight gain among overweight/obese women.

Pilot Feasibility Studies of Lifestyle Intervention Trials Designed to Reduce GDM Risk

Promising findings from several pilot feasibility studies have also been recently published. Korpi-Hyovalti ¹⁴⁷ randomized 54 women at high risk for GDM in Finland to a lifestyle intervention consisting of healthy lifestyle counseling (approximately 12 sessions), including compliance with dietary recommendations and moderate physical activity, or to a single session of lifestyle advice. The intervention began in early pregnancy (8-12 weeks gestation) and continued until routine screening for GDM (26-28 weeks gestation). Although there were no statistically significant differences between arms in terms of glucose tolerance, the lifestyle intervention group had a tendency toward lower weight gain (11.4 ± 6.0 kg vs 13.9 ± 5.1 kg; P = .062, adjusted for prepregnancy weight) as compared with the single-session group.

Callaway et al ⁹³ conducted a randomized controlled trial among 50 obese pregnant women in Australia. Women were randomized to an individualized exercise program with an energy expenditure goal of 900 kcal per week or to routine obstetric care. Although insulin resistance did not differ between the 2 groups, the intervention arm experienced a modest increase in physical activity. A total of 73% of women in the intervention group achieved more than 900 kcal per week of exercise-based activity at 28 weeks compared with 42% in the control arm (P = .047).

Wolff et al ⁷⁸ conducted a randomized controlled trial of a dietary intervention among 50 non-Hispanic, white, obese pregnant women. Women were randomized to a gestational weight gain target of 6 to 7 kg via 10 one-hour dietary consultations or to standard care. The women in the intervention group limited their energy intake and had lower gestational weight gain (6.6 kg vs 13.3 kg) compared with those in the standard care group. At 36 weeks of gestation, fasting insulin was reduced by 23% (−25 pmol/L; P = .022), and fasting glucose was reduced by 8% (−0.3 mmol/L; P = .03) compared with the standard care group.

Ongoing Randomized Trials of Lifestyle Interventions Designed to Reduce GDM Risk

Several ongoing interventions are currently investigating the impact of lifestyle changes on GDM risk.^94,95 The Behaviors Affecting Baby and You (B.A.B.Y) Study is an ongoing exercise trial among an ethnically diverse sample of prenatal care patients in Western Massachusetts at high risk of GDM. ⁹⁴ Women are randomized to a 12-week motivationally targeted, individually tailored physical activity intervention involving multimodal contacts (in person, mail, and telephone) or to a comparison health and wellness intervention. The overall goal of the exercise intervention is to encourage pregnant women to achieve the American College of Obstetricians and Gynecologists (ACOG) guidelines for physical activity during pregnancy through increasing walking and developing a more active lifestyle. The intervention is matched to the individual’s stage of motivational readiness for physical activity adoption and is based on the transtheoretical model ⁹⁶ and social cognitive theory. ⁹⁷ The intervention takes into account the specific social, cultural, economic, and physical environmental challenges faced by pregnant women of diverse socioeconomic and ethnic backgrounds. FitFor2 Study ⁹⁵ is an ongoing intervention study in Amsterdam, The Netherlands, designed to assess whether a prenatal exercise program will improve insulin sensitivity and fasting plasma glucose levels. Women are randomized to an intervention group that receives an exercise program consisting of aerobic and strength exercises twice per week or to usual care.

In summary, few lifestyle interventions targeting risk of GDM have been published. Instead, studies have been limited to relatively small dietary interventions or pilot feasibility studies. Studies targeting gestational weight gain hold promise but have not consistently evaluated the subsequent impact of changes in weight gain on GDM risk. Findings from larger, ongoing studies such as the B.A.B.Y. Study and FitFor2 Study will be critical in adding to the sparse literature on the efficacy of lifestyle intervention trials designed to prevent GDM.

Summary of Observational and Interventional Research

Accumulating evidence from observational studies suggests that several modifiable factors, particularly recreational physical activity before and during pregnancy, pregravid dietary patterns, and gestational weight gain, may be related to GDM risk. In light of these observations, the potential for lifestyle interventions that integrate appropriate dietary and physical activity strategies to reduce excessive maternal weight gain and GDM risk is high. Recent trials, although small in number, suggest that targeting high-risk groups may be effective. Further trials with larger sample sizes and longer follow-up are required to make more definitive conclusions. Such evidence-based lifestyle prevention programs for GDM could yield guidelines for frequency, intensity, duration, and type of physical activity as well as dietary composition and therefore inform clinical practice.

Barriers and Facilitators to Translation of Research Findings/Dissemination

Patient Compliance with Exercise, Diet, and Gestational Weight Gain Guidelines

Compliance with guidelines for gestational weight gain, physical activity, and a healthy diet among pregnant women in the United States is low. The ACOG recommends that pregnant women without medical or obstetrical complications engage in 30 minutes or more of moderate-intensity physical activity (eg, brisk walking) during most days of the week. ⁹⁸ This approach, which emphasizes the accumulation of physical activity (eg, through 10-minute bouts) may be more acceptable to pregnant women than traditional exercise recommendations. However, the majority of pregnant women in the United States are inactive, ⁹⁹ with minority women reporting lower levels of recreational physical activity during pregnancy as compared with nonminority women. ¹⁰⁰ For example, based on data from the 2000 Behavioral Risk Factor Surveillance System, 10.6% ± 3.0% of Hispanic pregnant women met physical activity guidelines compared with 16.7% ± 1.5% of non-Hispanic, white pregnant women. ¹⁰¹ In Proyecto Buena Salud, ¹⁰² an ongoing cohort of Hispanic pregnant women, only 5.2% of women reported meeting ACOG guidelines based on the Pregnancy Physical Activity Questionnaire. ¹⁰³ There is also evidence that physical activity, particularly recreational activity, tends to decline with the onset of pregnancy as well as over the course of pregnancy.^102,104,105

Little is known about compliance with recommended diet during pregnancy. Dietary behaviors among pregnant women were found to be of low quality in the Pregnancy, Infection, and Nutrition Study, with low-nutrient-dense foods being the major contributors to total energy, fat, and carbohydrates, whereas fortified foods were important sources of iron, folate, and vitamin C. The median dietary intakes of iron were below the recommended levels. ¹⁰⁶ A number of studies have also shown that pregnant teenagers consume inadequate servings of important food groups and have inadequate nutrient intake. ¹⁰⁷

Recently, the IOM issued new recommendations for gestational weight gain, including specific recommendations for rate of weight gain by prepregnancy BMI as well as specifying a new upper weight-gain limit of 9 kg (20 lb) for obese pregnant women. ⁶¹ However, prior studies have observed high rates of gestational weight gain both below and above the 1990 IOM recommended ranges, with one half to two thirds of pregnant women exceeding guidelines.^53,108 Rates of noncompliance are higher among particular ethnic groups, such as Hispanics with, for example, 52% of overweight and 75% of obese Hispanic women exceeding 1990 IOM guidelines ¹⁰⁹ and 19% to 29% of Hispanics failing to achieve guidelines.^{60,108,110,111}

Provider Counseling on Exercise, Diet, and Gestational Weight Gain

Although studies have shown that pregnancy exercise, diet, and gestational weight gain are influenced by health care provider recommendations, approximately one third of women reported that they did not receive counseling regarding these factors. ¹¹² Similarly, surveys of obstetricians and other providers indicate that a significant proportion of providers report not discussing exercise with their pregnant patients. ¹¹³ Approximately 30% to 60% of pregnant women report that they did not receive weight gain advice, and, among those patients who received advice, approximately one third reported receiving advice that was inconsistent with IOM guidelines.^111,114,115

There are several important barriers to the provision of behavioral counseling and related educational materials. Prenatal care providers face limited time within the constraints of clinical practices. Other reported barriers include insufficient training, concern about the sensitivity of the topic, the perception that counseling is ineffective, and lack of third-party-payer reimbursement. ¹¹⁶

Differences between practice patterns and current guidelines for exercise, diet, and gestational weight gain point to the need for increased dissemination of current recommendations. Continuing education as well as the development of standardized intake and counseling tools for health care providers may facilitate appropriate screening and behavioral counseling for pregnant women. ¹¹³

Pharmacotherapy

Lifestyle modification for GDM prevention may be preferable to pharmacotherapy for several reasons. The use of daily pharmacotherapy agents might not be appropriate for women of reproductive age planning a subsequent pregnancy. Lifestyle modification interventions that counsel women to increase their physical activity and make healthy dietary changes also have the potential to positively affect the behaviors of the participant’s entire family. ¹¹⁷

Pregnancy as a “Teachable Moment”

A facilitator to lifestyle change in pregnancy is the rapidly changing context of pregnancy, which brings opportunities for adoption and maintenance of new behaviors. Pregnant women more readily seek and have access to medical care and are often highly motivated to make healthy lifestyle changes for both their own health and that of their offspring. Thus, pregnancy may be a critical opportunity for both short- and long-term behavior modification representing a window of opportunity for health care providers to change lifestyle patterns toward the acquisition of healthier habits.^118,119

Recruitment and Retention

More research is needed to identify the most effective lifestyle interventions for the promotion of appropriate diet, physical activity, and gestational weight gain in the context of the current US health care system. It is likely that low-cost, high-reach lifestyle interventions will be most efficacious in this setting. Issues of recruitment and retention are critical; however, to date, patient adherence to recommended strategies, particularly among diverse patient populations, remains understudied.

Special challenges are encountered when recruitment into lifestyle interventions targets a physician practice-based population, particularly when the focus is on recruiting ethnic/racial minorities who may be at high risk of GDM. ¹²⁰ For example, lower levels of literacy and health literacy; ineffective communication and informed consent procedures by research staff; lack of, or poor quality, incentives; cumbersome protocols; and failure to provide accessible sites for participation have been cited as reasons for low participation in behavioral trials among Hispanics. ¹²¹

Adherence to behavioral interventions that are clinic-based and include multiple counseling sessions with extended periods of follow-up may be inherently difficult for women in the low-income group or who are already caring for young children. The time and child care pressures that women of reproductive age report as barriers to physical activity ¹²² suggest that the requirement to attend exercise groups at scheduled times and to travel to and from venues would deter many. In addition, financial barriers may preclude patients from being able to afford the cost of transportation to attend clinic visits. ¹²⁰ Indeed, retention levels in supervised group physical activity programs have been observed to fall to approximately 50% after 6 months.^123,124

Recommendations for Future Lifestyle Interventions

Novel Intervention Techniques

Tailored home-based lifestyle interventions that use the telephone, text messaging, MP3 players, e-mail, or an interactive Web site may be more effective for achieving lifestyle changes in pregnant women. Such interventions specifically designed for pregnant women might be a promising approach to improve recruitment and retention rates in future trials through their potential to increase compliance. Attention to the cultural, social, and contextual factors identified in qualitative research would also improve intervention design and implementation.

Recent pilot feasibility studies have explored novel techniques for increasing physical activity during pregnancy. For example, Lewis et al ¹²⁵ conducted a pilot study of a motivationally tailored, telephone-based exercise intervention for pregnant women. Telephone sessions of 10 to 15 minutes in duration were delivered weekly during the first month and biweekly during months 2 and 3. Each session included behavioral strategies based on Stage of Change Theory and the Transtheoretical Model. In addition to the telephone sessions, exercise information was mailed to participants (eg, tips for adopting and maintaining exercise, how to enlist social support, rewarding oneself for exercising, and time management tips). Participants also recorded their exercise each day in a written log. The authors found that pregnant participants significantly increased their exercise over the 3-month intervention period from a mean (standard deviation) of 60.47 (63.1) min/wk at baseline to 132.9 (82.3) min/wk at 3 months (P < .01). However, this study was limited by the lack of a control group.

In another innovative pilot study, Hausenblas et al ¹²⁶ randomly assigned pregnant women to watch a personally tailored exercise-related compact disc read-only memory (CD-ROM) designed to motivate participants to exercise. The authors found significant increases in exercise self-efficacy and knowledge in the intervention group as compared with the control arm. This interactive multimedia approach could be a cost- effective intervention for pregnant women for whom it is often impractical to recommend group and community-based exercise.

Pilot lifestyle interventions involving both physical activity and diet also show promising results. Hui et al ¹²⁷ conducted a pilot study of a community-based exercise and dietary intervention during pregnancy targeted at socioeconomically deprived pregnant Canadian women living in an urban area. The intervention included weekly group exercise sessions held in a community center as well as video exercise instruction to assist participants with home-based exercise. At the end of the intervention, physical activity levels were higher than baseline in the intervention group (P < .01) but not in the standard-of-care group. Favorable trends, although not statistically significant, were observed for reduction of excessive weight gain (21% in the intervention arm vs 33% in the standard-of-care group; P = .70) and GDM risk (4% in the intervention arm vs 10% in the standard-of-care group; P = .50).

In another pilot lifestyle intervention, Jackson et al ¹²⁸ evaluated a prenatal Video Doctor intervention designed to improve exercise and dietary behaviors in a low-income, ethnically diverse group of pregnant women. Brief messages about diet, exercise, and weight gain were delivered by an actor- portrayed Video Doctor twice during pregnancy. In the Video Doctor group (n = 158), there were statistically significant increases from baseline in exercise (28 minutes), intake of fruits and vegetables, whole grains, fish, and avocado and nuts, and significant decreases in intake of sugary foods, refined grains, high-fat meats, fried foods, solid fats, and fast food. In contrast, there were no changes from baseline for any of these outcomes in the usual care group (n = 163). The Video Doctor approach is promising, as it can easily be integrated into prenatal care to assist clinicians with effective diet and exercise counseling.

Lifestyle Interventions for the Prepregnancy and Pregnancy Periods

Future lifestyle interventions that target physical activity, diet, and gestational weight gain using behavioral strategies have the potential to prevent GDM and related comorbidities in women. Subsequent evidence-based intervention studies should be designed to evaluate the frequency, intensity, duration, and type of physical activity necessary to optimize maternal and fetal outcomes among women at risk for GDM. For example, such programs should evaluate the effect of exercise programs of differing intensities as well as active-living activities such as walking, gardening, and household activities. ¹²⁹

Future dietary intervention studies are critical to assess the effects of particular macronutrients and dietary patterns on GDM prevention. The effectiveness of dietary interventions for overweight or obese women should also be assessed. ⁷² Finally, given that each subsequent pregnancy is associated with greater postpartum weight retention, coupled with the increasing incidence of maternal obesity in the United States, a greater focus should be placed on evaluating the impact of pregnancy diet and exercise interventions on excessive maternal weight gain. ¹³⁰ Understanding the pattern of gestational weight gain in terms of risk for GDM will inform nutritional prevention strategies, and it will be critical to assess if compliance with the new IOM recommendations result in lower risk of GDM. ³⁸

In a similar vein, pregravid lifestyle interventions could be critical in preparing women for appropriate gestational weight gain through positive changes in diet and exercise behaviors prior to conception. Indeed, the current guidelines from the ACOG recommend that women be counseled prior to conception and encouraged to adopt lifestyle changes to minimize the risk of pregnancy complications related to being overweight or obese. ¹³¹ Similarly, the American Dietetic Association and the American Society of Nutrition recently proposed that all overweight women and obese women of reproductive age receive counseling prior to pregnancy, during pregnancy, and in the interconceptional period on the roles of diet and physical activity in reproductive health in order to ameliorate adverse outcomes. ³⁸

Prevention of Progression to Type 2 Diabetes

Although lifestyle interventions involving exercise and a healthy diet in adults have been found to reduce progression to type 2 diabetes by more than 50%,^14,132-134 little attention has been given to the potential benefits of such strategies in postpartum women. The DPP ¹³⁵ found that women with a self-reported history of GDM (a subset of the population, n = 350/2190) experienced a 53% reduction in the development of type 2 diabetes with the lifestyle intervention as compared with the placebo group even though they lost less weight than the general DPP population. However, this study involved an intensive intervention not easily administered in a clinical setting and was conducted an average of 12 years after GDM diagnosis such that intervening lifestyle factors and subsequent pregnancies may have modified findings. For example, women with early postpartum conversion to diabetes, and therefore at highest risk, were not eligible.

Other studies explored the use of pharmacological agents to prevent diabetes in women with GDM (eg, the Troglitazone in Prevention of Diabetes study) ¹³⁶ and found a reduction in the cumulative incidence of diabetes compared with placebo, but troglitazone has since been discontinued.

Weight loss can be achieved in the immediate postpartum period, ¹³⁷ with studies finding that both caloric restriction as well as physical activity are needed to reduce weight^138,139 as compared with exercise interventions alone. ¹⁴⁰ Similarly, weight loss interventions among nonpregnant adults^141-143 have shown that multifaceted interventions compared with stand-alone dietary advice, exercise modification, or behavioral strategies yield significant improvements in health outcomes and weight loss.

Recently, Ferrara and Ehrlich ¹¹⁷ assessed the feasibility of a prenatal/postpartum intervention involving physical activity and diet among women with GDM. The goal was to help women return to their prepregnancy weight, if it was normal, or achieve a 5% reduction from prepregnancy weight if overweight. The proportion of women who reached the postpartum weight goal was higher, although not statistically significant, in the intervention condition than in the usual care condition (37.5% vs 21.4%, absolute difference = 16.1%; P = 0.07). The intervention condition decreased dietary fat intake more than the usual care; however, no differences in postpartum physical activity were observed between conditions. This study suggests that a lifestyle intervention that starts during pregnancy and continues postpartum is feasible and may prevent pregnancy weight retention and help overweight women lose weight. A recent review calculated that, collectively, lifestyle interventions for women with a history of GDM could delay or prevent one sixth of type 2 diabetes cases in the female population. ¹⁴⁴

In summary, postpartum lifestyle interventions are critical in light of recent findings from long-term follow-up studies that a significant proportion of women with GDM go on to develop type 2 diabetes, especially during the first decade after the index pregnancy. Therefore, GDM offers an important opportunity for the development, testing, and implementation of clinical strategies for diabetes prevention. ¹⁴⁵ In addition, women who exceed gestational weight gain guidelines are more likely to experience postpartum weight retention, which itself, in turn, is associated with negative metabolic consequences for the mother. Therefore, women should be informed of their risks and empowered to make postpartum lifestyle changes.

Conclusions

Although there is evidence that type 2 diabetes can be prevented or delayed by lifestyle changes, including increased physical activity, improvements in diet, and modest weight loss in high-risk individuals,^14,132 to date, few studies have assessed whether GDM can be prevented by lifestyle changes in women at high risk for GDM. In light of the increasing prevalence of GDM and its risk factors, the need to identify strategies that might prevent GDM and its short- and long-term adverse health outcomes for both the mother and her offspring becomes critical. Currently, patient compliance with guidelines for gestational weight gain, physical activity, and diet are low, and providers may not be sharing guidelines with women. Thus, translating research findings into clinical practice remains a challenge.^118,146 As long-term follow-up studies reveal that a significant proportion of women with GDM go on to develop diabetes outside of pregnancy, especially during the first decade after the index pregnancy, GDM offers an important opportunity for the development, testing, and implementation of clinical strategies for diabetes prevention. ¹⁴⁵ Ongoing and future well- controlled intervention studies in this area will inform lifestyle intervention programs designed to prevent the incidence of GDM in women at high risk of this disorder.