Assiamira Ferrara1 and Samantha F. Ehrlich
(1)
Division of Research, Kaiser Permanente Northern California, Oakland, CA, USA
Assiamira Ferrara
Email: Assiamira.Ferrara@nsmtp.kp.org
Abstract
Women with a history of gestational diabetes (GDM) are at increased risk of later developing type 2 diabetes. Lifestyle modification interventions promoting weight loss and pharmacotherapy interventions to improve insulin sensitivity have been shown to be effective in preventing or delaying the onset of type 2 diabetes in older women with impaired glucose tolerance and/or a previous pregnancy complicated by GDM. This chapter reviews interventions aimed at reducing the incidence of type 2 diabetes for women with a history of GDM. The chapter also presents the few available, small-scale lifestyle interventions for weight management during pregnancy and/or during the early postpartum period; these potential interventions could be applied to women soon after a diagnosis of GDM in order to reduce their lifetime risk of developing type 2 diabetes. We present evidence supporting a lifestyle modification intervention that would begin during pregnancy and continue through the postpartum period, as pharmacotherapy interventions may not be appropriate for pregnant women or women of reproductive age who may intend to become pregnant. However, young women with GDM may not be aware of their diabetes risk and may perceive difficulty in changing lifestyle behaviors. Thus, novel approaches are necessary to translate lifestyle modifications previously proven effective in older women with impaired glucose tolerance to younger women with a recent history of GDM, particularly those with normal glucose tolerance postpartum. Directions for future research include randomized clinical trials assessing the effectiveness of lifestyle modification interventions targeting women with current GDM or a recent pregnancy complicated by GDM. Understanding the barriers to increasing physical activity and adopting a healthy diet, and learning how preventative lifestyle modifications may best be integrated into the busy schedules of young women caring for young children, are crucial.
24.1 Women with a History of GDM: Interventions to Prevent Type 2 Diabetes
24.1.1 Introduction
Women with a history of gestational diabetes (GDM) are at increased risk of later developing type 2 diabetes. Lifestyle modification interventions promoting weight loss and pharmacotherapy interventions to improve insulin sensitivity have been shown to be effective in preventing or delaying the onset of type 2 diabetes in older women with impaired glucose tolerance and/or a previous pregnancy complicated by GDM.
This chapter reviews interventions aimed at reducing the incidence of type 2 diabetes in women with a history of GDM. The chapter also presents the few available, small-scale lifestyle interventions for weight management during pregnancy and/or during the early postpartum period; these potential interventions could be applied to women soon after a diagnosis of GDM in order to reduce their lifetime risk of developing type 2 diabetes.
We present evidence supporting a lifestyle modification intervention that would begin during pregnancy and continue through the postpartum period, as pharmacotherapy interventions may not be appropriate for pregnant women or women of reproductive age who may intend to become pregnant. However, young women with GDM may not be aware of their diabetes risk and may perceive difficulty in changing lifestyle behaviors. Thus, novel approaches are necessary to translate lifestyle modifications previously proven effective in older women with impaired glucose tolerance to younger women with a recent history of GDM, particularly those with normal glucose tolerance postpartum. Directions for future research include randomized clinical trials assessing the effectiveness of lifestyle modification interventions targeting women with current GDM or a recent pregnancy complicated by GDM. Understanding the barriers to increasing physical activity and adopting a healthy diet, and learning how preventative lifestyle modifications may best be integrated into the busy schedules of young women caring for young children, are crucial.
24.2 The Risk of Type 2 Diabetes in Women with a History of Gestational Diabetes: Why, When, and for Whom Should we Intervene?
Screening for GDM may identify up to 31% of parous women who will develop type 2 diabetes at some point in their lifetime1 and has the added advantage of identifying a vast majority of these women prior to the development of abnormal glycemia in a nonpregnant state. Thus, women with a history of GDM are excellent candidates for interventions that aim to prevent the development of type 2 diabetes.2, 3Estimates of the relative risk for developing type 2 diabetes among women with a history of GDM range from 3 to 20, which are comparable in magnitude to the risks observed among individuals with impaired glucose tolerance, impaired fasting glucose, or both (3.5–8.6, 5.1–9.9 and 5.5–20.1, respectively).4 A recent meta-analysis reports that women with GDM have 7.4 times the risk of developing type 2 diabetes relative to women with normoglycemic pregnancies.2 In the Diabetes Prevention Program, the estimated cumulative incidence of diabetes was 38.4% for women with a history of GDM and 25.7% for parous women without a history of GDM.5 Thus, despite both groups having similar levels of impaired glucose tolerance at study entry, and women with a history of GDM being younger, women with a history of GDM had a 71% increased incidence rate compared with women without such a history.5 These data suggest that a pregnancy complicated by GDM adds additional risk.
Studies conducted among a broad distribution of ethnicities and geographical locations have all reported an increased risk for post-delivery development of diabetes among women with a history of GDM.6Women with GDM have reduced insulin secretion during pregnancy7 and the postpartum risk of type 2 diabetes has been shown to increase with decreasing insulin secretion in response to an oral glucose tolerance test in the pregnant state.8,9 This reduction in insulin secretion is likely to contribute to the later development of type 2 diabetes, particularly among women with behavioral factors that further decrease insulin sensitivity, such as excessive gestational weight gain, pregnancy weight retention, physical inactivity and increased caloric intake.
A systematic review6 of studies investigating the incidence of postpartum type 2 diabetes in women with a history of GDM reported that 5–10% of women with a history of GDM develop type 2 diabetes during the first year postpartum, while 50% develop type 2 diabetes in the 5 years following delivery.6 After controlling for variable testing rates and lengths of follow up between and within studies, progression to type 2 diabetes increased steeply in the first 5 years postpartum and then appeared to plateau.6 These data suggest that women with GDM would benefit most from intervention strategies to prevent or delay the onset of type 2 diabetes that are initiated soon after a diagnosis of GDM rather than years later. Early intervention also makes sense physiologically. In women with a history of GDM, the development of type 2 diabetes is correlated with progressive pancreatic β-cell failure to compensate for ongoing insulin resistance.5 Thus, for optimal success, interventions aimed at preventing or delaying the development of type 2 diabetes should be initiated as early as possible to avoid prolonged exposure to insulin resistance and the resulting β-cell deterioration.
Although the carbohydrate intolerance brought on by pregnancy usually resolves after delivery,10,11 approximately one third of women diagnosed with GDM will be diagnosed with impaired fasting glucose or impaired glucose tolerance at postpartum screening.12,13 Women with a history of GDM with normal postpartum screening results (i.e., those not diagnosed with impaired glucose tolerance or impaired fasting glucose in the postpartum) may be at lower risk for developing type 2 diabetes in the short term, but remain at increased risk for developing type 2 diabetes in the long term when compared with women without a history of GDM.2, 4 In fact, although 64.1% of women with GDM have normal postpartum screening and 21.8% have either impaired fasting glucose or impaired glucose tolerance,12, 13 up to 50% will develop type 2 diabetes in the 5 years after delivery.6 Therefore, all women with a history of GDM should be targeted for prevention strategies aimed at reducing the risk of developing type 2 diabetes later in life.
24.3 Women with a History of Gestational Diabetes: How Should we Intervene?
This section focuses on evidence supporting early initiation of prevention efforts, evidence from clinical trials investigating the effectiveness of prevention strategies, and offers suggestions for future directions of research.
Several observational studies provide evidence supporting a lifestyle intervention that starts soon after the diagnosis of GDM, and continues into the postpartum period. In women with GDM, antepartum predictive factors for future type 2 diabetes are elevated glucose levels, reduced insulin secretion, and obesity.9,14–20 The combination of prepregnancy obesity and reduced insulin secretion during pregnancy is associated with an eightfold increased risk of developing type 2 diabetes in the 5 years following a pregnancy complicated by GDM.8 Postpartum predictors of type 2 diabetes include elevated postpartum glucose levels that are below the diagnostic threshold for type 2 diabetes,15 obesity, and postpartum weight gain.21, 22 O’Sullivan21 found that after 23 years of follow-up on women with a history of GDM, type 2 diabetes was present in 61% of the women who were obese prior to pregnancy, in 42% of the women who had gained weight since pregnancy, and in only 28% of the women who were not obese or had lost weight since pregnancy. Peters22 also found that, among 666 Latino women with a recent history of GDM, postpartum weight gain of 4.5 kg was independently associated with a twofold increase in the risk of developing type 2 diabetes. Therefore, preventing weight gain and helping overweight/obese women with GDM to lose weight in the postpartum period might decrease their risk of developing type 2 diabetes.
Most women, including those with GDM, retain some of the weight they gained during pregnancy in the postpartum period. The 1988 National Maternal and Infant Health Survey23 demonstrates that pregnancy weight retention at 10–18 months postpartum is common, even among women who were not overweight prior to pregnancy. Among normal weight women (prepregnancy BMI 19.8–26.0) whose pregnancy weight gain met the Institute of Medicine’s (IOM) 1990 guidelines, only 28.9% returned to below their prepregnancy weight, while 51% retained between 0 and 3.63 kg, and 20.1% retained 4.08 kg or more of the weight they had gained during pregnancy. The same data23show greater pregnancy weight retention among women who were overweight prior to pregnancy (prepregnancy BMI 26.1–29.0) and who had also gained within the IOM 1990 guidelines24: 31.6% returned to below their prepregnancy weight and 32% retained between 0 and 3.63 kg, but 36.3% retained 4.08 kg or more. The authors also reported that pregnancy weight retention was higher (median value 2.6 kg) among women with gestational gains above the IOM recommendations.24
A study25 conducted among women with a history of GDM suggests that pregnancy weight retention is also of concern in this population. Among women with a history of GDM who had a prepregnancy BMI greater than 25.0, only 18% lost weight (≥5 kg) while 33% gained weight (≥5 kg) within the median observation time of 24 months post delivery.
Excessive weight gain during pregnancy (beyond the IOM guidelines) is a major risk factor for pregnancy weight retention in the postpartum period. In fact, the best predictor of pregnancy weight retention is excessive weight gain during pregnancy.26 In addition, pregnancy weight retention is associated with a woman being overweight in the long term27, 28 and overweight is a well established risk factor for developing type 2 diabetes. Preventing excessive gestational weight gain is also beneficial to women with GDM in terms of pregnancy outcomes.29, 30 Therefore, an intervention for women with GDM that aims to avoid excessive gestational weight gain and help women to return to their prepregnancy weight in the postpartum period, or lose additional weight if overweight prior to pregnancy, has the potential to prevent type 2 diabetes in both the short and long term. Given the pregnant and early postpartum state, behavioral interventions are preferred to pharmacological interventions, since the latter has the potential to harm developing fetuses or breastfeeding infants.
However, no lifestyle intervention trials among women with GDM that start during pregnancy or the early postpartum have been conducted and only a few small trials have focused on weight management, diet, or physical activity during pregnancy and/or early postpartum; only one of these focused on women with GDM.
24.4 Pregnancy Lifestyle Interventions
In a trial by Polley et al,31 120 normal weight and overweight women were randomized to either a behavioral intervention or usual care by 20 weeks gestation. The intervention women received education on pregnancy weight gain, healthy eating, and exercise and individual graphs of their weight gain progress. If they nevertheless exceeded their weight goals (i.e., gained more than the IOM recommendation for a given gestational week24), the intervention women received additional individualized nutrition and behavioral counseling. The intervention significantly decreased the percentage of normal weight women who exceeded the Institute of Medicine’s recommendations for total pregnancy weight gain. However, there was a nonsignificant effect in the opposite direction among overweight women, suggesting the need for additional support to promote appropriate pregnancy weight gain in that population.
On the other hand, in a randomized clinical trial conducted among obese women without GDM (n = 73), Wolff et al32 found that an intervention delivered through ten counseling sessions with a dietician with restriction of total energy intake was effective in reducing gestational weight gain (6.6 kg in women in the intervention group vs. 13.3 kg in the control group, p = 0.002).
A small non randomized study conducted among obese women with GDM compared a weight gain restriction program with and without supplemental physical activity and found that weight gain per week was significantly lower in the exercise group as compared with the diet-only group.33 However, women (n = 96) in this study selected their group assignments,33 so the observed difference in gestational weight gain could be attributed to factors other than physical activity. Although larger randomized clinical trials among women with GDM are needed, the results of these studies suggest that a pregnancy intervention combining diet and physical activity might be successful in limiting gestational weight gain in this population.
24.5 Early Postpartum: Lifestyle Interventions
Returning to prepregnancy weight soon after delivery, or below, if the woman was obese or overweight prior to pregnancy, might lower a woman’s risk for type 2 diabetes by reducing her risk of being overweight. Unfortunately, there are only a few, small randomized studies34–37 examining behavioral interventions for weight loss in the early postpartum period, and none are specific to women with a history of GDM.
Lovelady et al37 randomized 33 previously sedentary women who were 6–8 weeks postpartum and exclusively breastfeeding to a 12-week exercise program or to a control group. The exercise program consisted of 45 min a day of aerobic exercise, performed 5 days a week. The authors found a significant decline in weight and percent body fat for the entire study population, but no significant differences between the exercise and the control groups. Although women in the exercise group had higher energy expenditure, they compensated with higher energy intake. The results of this study suggest that aerobic exercise alone, without diet modification, is insufficient to promote postpartum weight loss. Lovelady et al36 conducted another trial in which 40 overweight, exclusively breastfeeding postpartum women were randomized at 4 weeks postpartum to either a diet and exercise intervention group or a control group. The diet and exercise program lasted for 10 weeks, during which time the women were instructed to reduce their energy intake by 500 kcal/day and to exercise for 45 min a day, 4 days a week. Women in the intervention group lost significantly more weight and fat mass than control women; 48% of the women in the diet and exercise group were within 1 kg of their prepregnancy weight by the end of the study period, compared with 21% of the women in the control group. Although women in the diet and exercise group decreased their energy intake more than women in the control group, the difference was not statistically significant, which could be due to the small sample size. Taken together, the results of the two Lovelady studies36, 37 suggest that an intervention which combines diet and physical activity may be the best strategy for achieving postpartum weight loss.
O’Toole et al34 conducted a randomized trial that investigated a diet and physical activity intervention for weight loss in the first year postpartum among overweight women. The 13 women in the intervention group experienced significant weight loss (7.3 kg on average) by 1 year postpartum, while the 10 women in the control group had only a small, nonsignificant reduction in weight (1.3 kg on average). Leermakers et al35 randomized 90 women who had given birth in the previous 3–12 months to either a no-treatment control group or a behavioral weight loss intervention that focused on a low-fat/low-calorie diet and increasing physical activity. Women in the behavioral intervention group lost significantly more weight than controls (7.8 kg vs. 4.9 kg). The amount of weight retained at baseline emerged as the single strongest predictor of how close a woman came to reaching her prepregnancy weight. These results provide additional support for initiating lifestyle modification interventions early in the postpartum period, in order to maximize success.
Behavioral interventions targeting postpartum women, including those with a history of GDM, are particularly challenging to implement due to the considerable life changes that occur in the postpartum period. Previous trials34,35 evaluating behavioral interventions for postpartum women, which incorporated education, goal setting, counseling, and follow-up via telephone or mailings, obtained only modest success in helping women reach their weight and physical activity goals. A number also saw high attrition rates: 4234 and 31%.35 Compliance with behavioral interventions, which typically include multiple counseling sessions and extended periods of follow-up, may be inherently difficult for women with infants or young children.
Albright et al38 conducted a small observational study among postpartum women to compare pre-intervention to post-intervention minutes of moderate and vigorous leisure-time physical activity. The 2-month intervention relied primarily on email and weekly telephone counseling contacts to promote physical activity; all participants also received a pedometer to provide them with an objective measure of the number of steps they accumulated each day. At baseline, participants reported a mean of 3 ± 13.4 min/week of moderate and vigorous leisure-time physical activity. Minutes per week were significantly higher post-intervention: 85.5 ± 76.4 min/week (p < 0.001), leading the authors to conclude that a telephone/email intervention tailored to the needs of postpartum women effectively increased levels of physical activity. Project Viva,39 which explored longitudinal changes in physical activity from prepregnancy to the postpartum period, reported that women decreased their moderate and vigorous physical activity but maintained levels of walking. A small study assessing the exercise beliefs of women with GDM found that the most common barrier to exercise in the postpartum period was a lack of time.40 A diet and physical activity intervention, administered through telephone and email contacts that emphasizes walking or other forms of physical activity that can be done with an infant, may be more effective in this population.
24.6 Late Postpartum: Lifestyle and Pharmacotherapy Interventions
The Diabetes Prevention Program (DPP)41 was a randomized, controlled clinical trial conducted among men and women with impaired glucose tolerance, elevated fasting blood glucose levels, and a BMI >24 (or >22 among Asians), including women with a history of GDM. The DPP41 investigated the efficacy of metformin therapy and an intensive lifestyle intervention versus placebo in delaying or preventing the development of diabetes. The intensive lifestyle intervention aimed to achieve and maintain: (1) weight reduction of at least 7% of initial body weight through healthy eating and physical activity, and (2) at least 150 min/week of moderate intensity physical activity, such as walking or bicycling.41 The intensive lifestyle intervention included training on diet, exercise, and behavior modification skills and was delivered through a structured protocol that included strategies for individually tailoring the intervention, in an attempt to maximize participant success. In analyses conducted among the entire DPP study population, the intensive lifestyle intervention significantly reduced the incidence of diabetes by 58% relative to the placebo control group, while metformin plus the standard lifestyle intervention reduced the incidence by 31%.41
The Diabetes Prevention Program Research Group also conducted subgroup analyses comparing parous women enrolled in the DPP with a history of GDM to parous women enrolled in the DPP without a history of GDM.5 The two groups of women were comparable with respect to parity, BMI, fasting glucose, 2-h post-load glucose, glycosylated hemoglobin, insulin sensitivity, and insulin secretion at randomization, but differed in age: women with a history of GDM were significantly younger than parous women without a history of GDM (43 vs. 51 years, on average).
The results of this study also suggest that, among women with history of GDM, intensive lifestyle intervention and metformin are equally effective in decreasing the risk of developing type 2 diabetes.5 In women with a history of GDM, the intensive lifestyle intervention resulted in a significant 53% reduction in risk when compared with placebo, whereas metformin resulted in a statistically significant 50% reduction in risk. Among women without a history of GDM, those in the intensive lifestyle intervention experienced a statistically significant 49% reduction in risk when compared with the placebo group; those taking metformin had a statistically significant 14% reduction in risk. Thus, the reduction in risk afforded by metformin was modified by history of GDM (50% in women with a history of GDM vs. 14% in those without, interaction p = 0.06). The greater effectiveness of metformin in women with history of GDM might be related to their younger age, since the analyses that included all DPP participants also suggested that metformin was more effective in younger men and women.41
However, women with a history of GDM were less successful in adhering to the intensive lifestyle intervention in the long-term than were women without a GDM history. Although women both with and without a history of GDM who were randomized to the intensive lifestyle intervention increased their physical activity by approximately 1.5 h/week in the first year, this increase was not sustained among women with a history of GDM, who fell to less than 30 min of increased physical activity per week by year 3 of the study. There were also differences in weight loss by history of GDM. Women with a history of GDM lost weight in the first 6 months of the intervention (maximum achieved weight loss: 5.13 ± 0.43 kg, mean ± SD), after which they began to steadily gain weight. Women without a history of GDM achieved most of their weight loss by 6 months but continued to lose weight at a lower rate through 1 year, after which they too, began to steadily gain weight (maximum achieved weight loss: 6.40 ± 0.20 kg). Thus, women with a history of GDM had a mean weight loss of only 1.60 kg (SD 0.80 kg) by year 3 of the study while those without a history of GDM had a mean weight loss of 4.03 kg (SD 0.40 kg) in the same interval (p = 0.021 for differences in weight at year 3). The intensive lifestyle intervention may have been more effective in preventing or delaying the development of type 2 diabetes among women with a history of GDM if they had been more able to adhere to the prescribed physical activity and weight loss. Again, it is possible that the lower level of adherence to physical activity and weight loss observed among women with a history of GDM was due to their younger age and presumably, busier postpartum lives.
It should be noted that an average of 12 years elapsed between the participants’ first GDM pregnancies and enrollment in the DPP. Since participation in the DPP also required impaired glucose tolerance with elevated fasting glucose, women with GDM who developed diabetes in the first few years following delivery were ineligible. The results of these subgroup analyses may only apply to a select group of women with a history of GDM: those who remained free of diabetes for 12 years, on average, following a pregnancy complicated by GDM.
The Troglitazone in Prevention of Diabetes (TRIPOD)42 was the first randomized control trial to examine the effectiveness of a pharmacotherapy intervention in delaying or preventing the development of diabetes among women with a history of GDM. Women were eligible for the trial if they had had a pregnancy complicated by GDM in the prior 4 years and if they were at high risk for developing type 2 diabetes in the subsequent 5 years, based on the results of a 75-g oral glucose tolerance test performed postpartum.15 A total of 266 high risk Hispanic women were randomized to receive either placebo or 400 mg/day of troglitazone, a thiazolidinedione. Thiazolidinediones improve insulin sensitivity and short-term treatment with troglitazone had been previously shown to reduce the secretory demands that insulin resistance places on pancreatic β-cells.43 The TRIPOD study42 aimed to test whether chronic treatment of insulin resistance with troglitazone could preserve β-cell function and delay or prevent type 2 diabetes.
After 28–30 months of follow up, the authors found a significantly lower cumulative incidence of diabetes among women receiving troglitazone as compared with women who received placebo (5.4 vs. 12.1%).42 Among the 236 women who returned for at least one follow up visit, troglitazone had reduced the incidence of diabetes by over 50%. However, protection required an initial increase in whole body insulin sensitivity; troglitazone therapy was most effective among women who responded to that increase with a large reduction in insulin output. One-third of the women in the troglitazone group failed to demonstrate initial increases in whole body insulin sensitivity, and relative to the placebo group, these women were not protected from diabetes. These non-responders were similar to women who did demonstrate initial increases in whole body insulin sensitivity in terms of baseline characteristics and compliance with troglitazone therapy. Thus, the authors were unable to identify any clinical or metabolic characteristics that could distinguish those who would be protected by troglitazone therapy from those who would not.
The TRIPOD trial42 was discontinued in March of 2000 when troglitazone was withdrawn from the market due to reports of hepatotoxicity. Eighty-four of the 102 women who reached the end the trial without developing diabetes returned for post-trial testing (40 in the placebo group and 44 in the troglitazone group). Returnees in the troglitazone group had an average annual incidence rate of diabetes of 3.1% in the post-trial period, while returnees from the placebo group had a significantly higher average annual incidence rate of 21.2%. Thus, the drug’s protective effect persisted for approximately 8 months after discontinuation of therapy. These findings led the authors to suggest that troglitazone had fundamentally transformed the underlying metabolic changes leading to the development of diabetes. They proposed that troglitazone therapy provided indirect protection that was mediated through improved whole body insulin sensitivity and resulted in β-cell rest.
24.7 Directions for Future Research
Lifestyle modification interventions that begin shortly after a diagnosis of GDM and continue into the postpartum period have the greatest potential for success in reducing the incidence of type 2 diabetes among all women with GDM. However, young women with a recent history of GDM may not appreciate their future risk of type 2 diabetes44 and may perceive difficulty in starting to exercise. Thus, unique approaches will be required to translate the prevention strategies shown to be effective among older patients with impaired glucose tolerance45 to younger women with a history of GDM. Interventions targeting this group must take into consideration the demands of being a new parent and the physical activity barriers specific to postpartum women, particularly the perceived lack of time to exercise40 and a lack of childcare.39 Interventions that utilize the telephone, text messaging, a MP3 player, email, or an interactive Web site may be more effective for achieving lifestyle change in young women with a recent history of GDM due to the unique barriers faced by postpartum women. Qualitative studies in the target population would help identify the preferred modalities of intervention delivery. Future interventions for weight management in women with a recent history of GDM should also provide a theoretical basis attempting to explain the mechanism by which the intervention is designed to work.46 Attention to the cultural, social, and contextual factors established in descriptive research would also improve intervention design and implementation.46
Lifestyle modification interventions for women with a recent history of GDM may be preferred to pharmacotherapy interventions for several reasons. As both intervention strategies are intended for women of reproductive age, the use of daily pharmacotherapy agents may be recommended only for women who will not become pregnant. Lifestyle modification interventions also have the potential to positively impact the children and families of women who participate: counseling women to increase their physical activity and make healthy dietary changes may potentially impact the health behaviors of the entire family. Research investigating the secondary, family-level effects of lifestyle modification interventions targeting postpartum women has yet to be conducted.
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