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Prevention of Diabetes in Women with a History of
Gestational Diabetes: Effects of Metformin and
Lifestyle Interventions
Robert E. Ratner, Costas A. Christophi, Boyd E. Metzger, Dana Dabelea, Peter H. Bennett,
Xavier Pi-Sunyer, Sarah Fowler, Steven E. Kahn, and The Diabetes Prevention Program Research Group*
Context: A past history of gestational diabetes mellitus (GDM) confers a very high risk of postpar-
tum development of diabetes, particularly type 2 diabetes.
Objective: The Diabetes Prevention Program (DPP) sought to identify individuals with impaired glucose
tolerance (IGT) and intervene in an effort to prevent or delay their progression to diabetes. This analysis
examined the differences between women enrolled in DPP with and without a reported history of GDM.
Design: The DPP was a randomized, controlled clinical trial.
Setting: The study was a multicenter, National Institutes of Health-sponsored trial carried out at
27 centers including academic and Indian Health Services sites.
Patients: A total of 2190 women were randomized into the DPP and provided information for past
history of GDM. This analysis addressed the differences between those 350 women providing a past
history of GDM and those 1416 women with a previous live birth but no history of GDM.
Interventions: Subjects were randomized to either standard lifestyle and placebo or metformin
therapy or to an intensive lifestyle intervention.
Main Outcomes: The primary outcome was the time to development of diabetes ascertained by
semiannual fasting plasma glucose and annual oral glucose tolerance testing. Assessments of
insulin secretion and insulin sensitivity were also performed.
Results: Whereas entering the study with similar glucose levels, women with a history of GDM ran-
domized to placebo had a crude incidence rate of diabetes 71% higher than that of women without
such a history. Among women reporting a history of GDM, both intensive lifestyle and metformin
therapy reduced the incidence of diabetes by approximately 50% compared with the placebo group,
whereas this reduction was 49 and 14%, respectively in parous women without GDM. These data suggest
that metformin may be more effective in women with a GDM history as compared with those without.
Conclusions: Progression to diabetes is more common in women with a history of GDM compared
with those without GDM history despite equivalent degrees of IGT at baseline. Both intensive
lifestyle and metformin are highly effective in delaying or preventing diabetes in women with IGT
and a history of GDM. (J Clin Endocrinol Metab 93: 4774–4779, 2008)
The original identification of gestational diabetes mellitus
(GDM) by O’Sullivan and Mahan in 1964 recognized this
population’s increased risk of the future development of diabetes
(1). Pregnant women undergoing a 3-h, 100-g oral glucose tol-
erance test with glucose values exceeding 2 SD above the mean on
two of the four values were defined as having GDM. In this
0021-972X/08/$15.00/0
Printed in U.S.A.
Copyright © 2008 by The Endocrine Society
doi: 10.1210/jc.2008-0772 Received April 9, 2008. Accepted September 19, 2008.
First Published Online September 30, 2008
*Author Affiliations are shown at the bottom of the page 4775
For editorial see page 4646
Abbreviations: BMI, Body mass index; DPP, Diabetes Prevention Program; GDM, gesta-
tional diabetes mellitus; HbA1c, glycosylated hemoglobin; IGT, impaired glucose tolerance;
ILS, intensive lifestyle; TRIPOD, Troglitazone in Prevention of Diabetes.
ORIGINAL ARTICLE
Endocrine Care
4774 jcem.endojournals.org J Clin Endocrinol Metab. December 2008, 93(12):4774–4779
landmark study, the investigators described a population of preg-
nant women with a lifetime risk of diabetes exceeding 70% (2).
In recognition of this marked risk for diabetes, the Diabetes
Prevention Program (DPP) sought to identify women with a pre-
vious history of GDM for inclusion in this large prospective study
of the ability of metformin therapy or intensive lifestyle (ILS) to
prevent diabetes in individuals with impaired glucose tolerance
(IGT) (3). The population enrolled included a multiethnic pop-
ulation of men and women spanning the age range of 25–89 yr
(4). As previously reported for the cohort as a whole, ILS reduced
the incidence of diabetes by 58%, whereas metformin reduced it
by 31%, compared with the placebo control group (5). We now
report a comparison of baseline characteristics and responses to
intervention in subgroups of women enrolled in DPP with a his-
tory of GDM compared with parous women in the DPP without
a history of GDM.
Subjects and Methods
Subjects
The DPP design, eligibility, and baseline characteristics have been
reported elsewhere (3, 4). The study prespecified a recruitment target and
planned hypotheses regarding women with a history of GDM. Briefly,
3234 participants with IGT were identified, qualified as having IGT by
a 2-h oral glucose tolerance test and randomized to three different treat-
ment groups (placebo, metformin, and ILS) in 27 clinical centers
throughout the United States. By entry criterion, all participants in DPP
were required to be older than 25 yr of age. Eligibility required a fasting
plasma glucose value of 95–125 mg/dl and a 2-h value, after a 75-g
glucose load, between 140 and 199 mg/dl. (The minimum fasting glucose
was not a requirement in the American Indian centers.) At the time of
randomization, all women completed a simple questionnaire relating to
their number of pregnancies and live births and whether they were com-
plicated by gestational diabetes. No further information on the index
pregnancies was possible due to the time past from the pregnancy until
recruitment. Of 2190 women in DPP, 350 reported a history of GDM
and 1840 did not. Of the 1840 women without history of GDM, 321 had
never been pregnant. Of the 1519 with pregnancies, 1416 had at least one
live birth. This report restricted analyses to the 1416 women without a
history of GDM reporting at least one live birth and all 350 women with
a history of GDM because all reported at least one live birth. Of the 350
women with a history of GDM, 122 were assigned to placebo, 111 to
metformin, and 117 to ILS, whereas among the 1416 women without a
history of GDM, 487 were assigned to placebo, 464 to metformin, and
465 to ILS.
Statistical analysis
Baseline characteristics were described using percentages for cate-
gorical variables and means ⫾SD for quantitative variables. For variables
with highly skewed distributions a logarithmic transformation was done
first, and the geometric means were reported instead. Comparisons
among groups were done using the
2
test of independence for categorical
variables and the ttest for quantitative variables.
Cox proportional hazards models (6) were used to assess the effect of
the treatment group on the development of diabetes. Analyses stratified
on reported history of GDM were performed, and a test of heterogeneity
was used to determine whether the effect of the treatment varied between
the subgroups based on GDM history, after adjusting for age at ran-
domization. Because interactions were examined as tests of hypotheses,
they were interpreted cautiously because of the multiplicity of such tests
in DPP analyses. Treatments were compared within each GDM subgroup
using the log-rank test. Similarly, analyses stratified on treatment group
were performed comparing the GDM subgroups within each treatment.
The impact of the interventions on the development of cardiovascular
risk factors in women with a history of GDM compared with women
without a history of GDM was evaluated with mixed-effects models (7)
that estimated mean differences over time in physical activity and weight,
adjusted for the baseline values as well as age at randomization. Gener-
alized estimating equations (8) were used to assess differences over time
in the percentage of participants with adherence to medication, adjusted
for age at randomization. Pvalues for comparisons between any two
groups were adjusted for multiple comparisons using the Holm proce-
dure (9).
AP⬍0.05 was considered to be statistically significant and all tests
were two sided. The Statistical Analysis Software (SAS) version 8.2 was
used for all analyses (SAS Institute, Inc., Cary, NC).
Results
Those women with a reported history of GDM enrolled in DPP
(n ⫽350) had a mean 12-yr interval (for n ⫽207 due to incom-
plete data) since the delivery of their first GDM pregnancy. They
were significantly younger than parous women (n ⫽1416) with-
out a GDM history (43.0 ⫾7.6 vs. 51.5 ⫾9.7 yr, P⬍0.001), so
baseline analyses were adjusted for age. Other characteristics
were comparable, including parity, body mass index (BMI), fast-
ing glucose, 2-h postglucose load glucose, glycosylated hemo-
globin (HbA1c), insulin sensitivity, and insulin secretion (Table
1). After adjusting for age, lipid levels were similar between those
with and without a history of GDM, with LDL-C levels (arith-
metic means ⫾SD) of 121.2 ⫾30.9 vs. 125.1 ⫾33.6 mg/dl,
HDL-C of 45.5 ⫾10.3 vs. 48.7 ⫾12.3 mg/dl, and triglycerides
(geometric means) of 135.3 vs. 140.3 mg/dl, respectively. Sys-
tolic blood pressure was lower in those with a history of GDM
(117.4 ⫾13.1 vs. 124.1 ⫾15.4 mm Hg, adjusted for age, P⫽
0.004). Ethnic distribution was similar in women with vs. with-
Medstar Research Institute (R.E.R.), Hyattsville, Maryland 20783; The Biostatistics Center (C.A.C., S.F.), Diabetes Prevention Program Coordinating Center, The George Washington
University, Rockville, Maryland 20852; Northwestern University Feinberg School of Medicine (B.E.M.), Chicago, Illinois 60611; Department of Preventive Medicine and Biometrics (D.D.),
University of Colorado, Denver, Colorado 80262; National Institute of Diabetes and Digestive and Kidney Diseases (P.H.B.), Phoenix, Arizona 85016; St. Luke’s-Roosevelt Hospital Center
(X.P.-S.), New York, New York 10019; and Veterans Affairs Puget Sound Health Care System and University of Washington (S.E.K.), Seattle, Washington 98108
TABLE 1. Baseline characteristics of parous women in DPP
History
of GDM
No history
of GDM Pvalue
n 350 1416
Age (yr) 43.0 ⫾7.6 51.5 ⫾9.7 ⬍0.001
Live births 2.61 ⫾1.32 2.63 ⫾1.49 0.794
BMI (kg/m
2
)34.2 ⫾6.2 34.6 ⫾6.8 0.379
Fasting glucose (mg/dl) 105.8 ⫾8.4 105.2 ⫾7.9 0.246
Two-hour glucose (mg/dl) 165.8 ⫾18.0 164.2 ⫾17.0 0.118
HbA1c (%) 5.87 ⫾0.50 5.91 ⫾0.49 0.105
Fasting insulin (
U/ml) 26.7 ⫾14.5 26.3 ⫾14.2 0.616
Insulin to glucose ratio
(
U/mg)
118.3 ⫾85.1 128.1 ⫾92.4 0.076
J Clin Endocrinol Metab, December 2008, 93(12):4774 – 4779 jcem.endojournals.org 4775
out a history of GDM (Fig. 1), with ethnic minority groups rep-
resenting 46% of women with a history of GDM.
Randomization resulted in balance by age, BMI, HbA1c, in-
sulin to glucose ratio, and reported history of GDM across the
three treatment groups. Medication adherence was similar be-
tween women with and without a history of GDM, with placebo
adherence (72.9 and 76.7%, respectively) significantly greater
(P⬍0.05) than metformin adherence (68.8 and 70.3%,
respectively).
Those women randomized to placebo therapy represent the
uninterrupted progression of glucose intolerance within the
DPP. Figure 2 illustrates the cumulative incidence of diabetes
development over time among parous women by history of
GDM. Three years after randomization, the estimated cumula-
tive incidence of diabetes was 38.4% for women with a history
of GDM compared with 25.7% for women without a history of
GDM. Despite both groups entering the study with similar glu-
cose levels, women with a history of GDM had a 71% increased
crude incidence rate per 100 person-years for the development of
diabetes compared with women without such a history.
Women randomized to ILS increased their physical activity
comparably during the first year of intervention (approximately
1.5 h/wk from baseline activity) in both the GDM and non-GDM
groups; however, this was not sustained by the women with a
history of GDM (Fig. 3B), falling to less than 30 min of increased
physical activity by yr 3. Additionally, as shown in Fig. 3, women
with a GDM history had a weight loss nadir of 5.13 ⫾0.43 kg
at 6 months with a steady weight regain to a mean weight loss of
only 1.60 ⫾0.80 kg at yr 3 compared with a nadir of 6.40 ⫾0.20
kg and a mean weight loss of 4.03 ⫾0.40 kg at yr 3 in those
women without a history of GDM (Fig. 3A) (P⫽0.021 for
differences in weight at 3 yr).
Figure 4 depicts the progression of IGT to diabetes by ran-
domized treatment in those women with and without a history
of GDM. Parous women without a history of GDM (Fig. 4A)
benefited from ILS, with a 49% risk reduction compared with
placebo (P⬍0.001) and a 41% risk reduction compared with
metformin (P⫽0.001). Unlike in the original complete DPP
cohort, we did not detect a significant benefit from metformin
therapy for this subgroup, with only a 14% risk reduction com-
pared with placebo, although our study was not adequately pow-
ered for this subgroup comparison. In contrast, among women
with a history of GDM (Fig. 4B), metformin afforded this group
a 50% risk reduction (P⫽0.006) compared with placebo,
whereas ILS achieved a 53% risk reduction (P⫽0.002).
Table 2 summarizes the observed hazard rates for the devel-
opment of diabetes in women with and without a history of
GDM, the impact of the therapeutic interventions, and the public
health implications of implementing these treatments. In the pla-
cebo group, a history of GDM conferred a significantly greater
incidence of progression from IGT to diabetes (15.2 cases per
100 person-years compared with 8.9 cases per 100 person-years,
P⬍0.05). Despite the difference in underlying hazard rate, ILS
had a similar impact on risk reduction (compared with placebo)
in the two groups (53.4 vs. 49.2%, interaction P⫽0.74),
whereas metformin tended to be more effective in reducing the
incidence of diabetes (compared with placebo) in those women
with a history of GDM (50.4 vs. 14.4%, interaction P⫽0.06) vs.
those without a history of GDM. Taking into account these treat-
ment effects, we estimate that only five to six women with IGT
and a history of GDM would need to be treated over 3 yr with
either metformin or ILS to prevent one case of diabetes. In
women without a history of GDM, the estimated numbers
needed to treat to prevent a single case of diabetes over 3 yr are
24 and nine for metformin and ILS, respectively.
Discussion
The historical observations of rapid and progressive develop-
ment of type 2 diabetes after pregnancy complicated by GDM (2,
10–12) encouraged DPP investigators to recruit such women
into the study. Our inclusion criteria required IGT with an
elevated fasting glucose and excluded those with diabetes,
thus excluding women with early postpartum conversion to
diabetes. Kjos et al. (13) described persistence of diabetes
postpartum occurring in as many as 10% of women with a
history of GDM and conversion to diabetes in those normal-
izing glycemia postpartum occurring quickly over the next
5–10 yr with a paucity of data beyond that time (14). The
mean age of women with a history of GDM entering DPP was
43 yr with a mean interval of 12 yr from the index GDM
pregnancy, suggesting that we may have excluded many
women with the highest risk of diabetes conversion. Despite
this and the fact that those reporting a history of GDM were
younger, the DPP subgroup with a history of GDM had a
crude incidence rate of diabetes that was 71% higher than that
Slice 2
18%
16%
Slice 3
17%
Slice 4
3%
Slice 5
7%
Women with history of GDM Women without history of GDM
American
Indian
7%
American
Indian
10%
Caucasian
50%
Caucasian
54%
African
American
23%
African
American
18%
Hispanic
American
17%
Hispanic
A
merican
16%
Asian
3%
Asian
2%
FIG. 1. Ethnic representation of parous women with and without a history of
GDM randomized into the DPP.
0
5
10
15
20
25
30
35
40
45
0 0.5 1 1.5 2 2.5 3
GDM
(n=122)
Non-GDM
(n=487)
Cumulative incidence (%)
Years from randomization
FIG. 2. Cumulative incidence of diabetes mellitus among the placebo group by
history of GDM.
4776 Ratner et al. Diabetes in Women with a History of GDM J Clin Endocrinol Metab, December 2008, 93(12):4774 – 4779
of parous women without a history of GDM. Even many years
after the pregnancy complicated by GDM, it appears that
women continue to be at risk for development of diabetes.
Therefore, continued follow-up and testing for diabetes
should be part of the lifetime assessment of women with a
history of GDM.
Although tests of interaction between the effect of interven-
tions and the history of GDM were not significant and the study
was not powered for these tests, our data suggest a differential
success of the interventions between those with and without his-
tory of GDM. Achieving targets for ILS was far less successful
among those with a history of GDM. On average, these women
were less able to sustain the prescribed level of physical activity
and demonstrated a lower peak weight loss as well as a more
rapid weight regain, resulting in a significantly lower weight loss
over time than women in the ILS group without a history of
GDM. Because weight loss was strongly associated with a re-
duced risk of diabetes in DPP (hazard ratio for 5 kg weight loss ⫽
0.42; 95% confidence interval 0.35–0.51, P⬍0.001), it is not
surprising that, within ILS, women with a history of GDM had
a higher crude incidence rate of diabetes than those without
(7.4 vs. 4.7 cases per 100 person-years, P⫽0.065). None-
theless, ILS remains an effective treatment modality for dia-
betes prevention among women with a history of GDM, re-
quiring therapy of only five women to prevent one case of
diabetes over a 3-yr period.
-7
-6
-5
-4
-3
-2
-1
0
1
00.511.522.53
Years from randomization
Change in weight (kg)
ILS
Placebo
Metformin
-7
-6
-5
-4
-3
-2
-1
0
1
00.511.522.53
Years from randomization
Change in weight (Kg)
ILS
Placebo
Metformin
A
B
FIG. 3. Change in weight during DPP by randomized treatment group. Panel A, Women without a history of GDM; Panel B, women with a history of GDM.
J Clin Endocrinol Metab, December 2008, 93(12):4774 – 4779 jcem.endojournals.org 4777
We estimate that metformin therapy, on the other hand,
may be as much as 3 times more effective in reducing the
incidence of diabetes in those with a history of GDM com-
pared with those without. This may in part be explained by the
younger age (mean of 43 yr) of the GDM group because
women between 25 and 44 yr of age within DPP as a whole had
a similar risk reduction with either metformin or ILS, but
metformin was no more effective than placebo in women over
age 60 yr (5).
The Troglitazone in Prevention of Diabetes (TRIPOD)
study data provide the closest comparison to the DPP results
(15). TRIPOD enrolled an exclusively Latina population,
whereas DPP was ethnically mixed with 54% Caucasian. In
the DPP, the GDM population was older (43 vs. 34 yr) and
considerably more distant from their index pregnancies (12
vs. ⬍4 yr). As a result, we lost those individuals converting to
diabetes in the early postpartum years before entering DPP.
Nevertheless, parous female DPP participants, both with and
without history of GDM, had a marked risk of progressing to
diabetes (15.2 and 8.9 cases per 100 person-years, respec-
tively) over the subsequent 3–5 yr. TRIPOD demonstrated a
55% risk reduction with troglitazone treatment, comparable
with our observed reductions of 50.4% for metformin and
53.4% for ILS among women with history of GDM.
0
5
10
15
20
25
30
35
40
45
0 0.5 1 1.5 2 2.5 3
Metformin
(n=464)
Placebo
(n=487)
ILS
(n=465)
Cumulative incidence (%)
Years from randomization
0
5
10
15
20
25
30
35
40
45
0 0.5 1 1.5 2 2.5 3
Years from randomization
Cumulative incidence (%)
Metformin
(n =111)
Placebo
(n=122)
ILS
(n=117)
A
B
FIG. 4. Cumulative incidence of diabetes in DPP by randomized treatment group. Panel A, Women without a history of GDM; Panel B, women with a history of GDM.
4778 Ratner et al. Diabetes in Women with a History of GDM J Clin Endocrinol Metab, December 2008, 93(12):4774 – 4779
In summary, in DPP, women with a reported history of
GDM had a markedly increased risk for diabetes compared
with parous women with a similar degree of glucose intoler-
ance and no GDM history. Intervention with metformin and
ILS were comparable in reducing the development of diabetes
with only an estimated five to six individuals requiring treat-
ment to prevent one case of diabetes over 3 yr. In women
without a history of GDM as well as in the DPP cohort overall,
ILS was found to be far more effective than metformin ther-
apy. In those with history of GDM, the absence of a difference
between ILS and metformin may be due to the minimal weight
loss achieved with ILS among GDM women. We conclude that
women with a history of GDM who currently have IGT re-
main at an increased risk of developing diabetes years after the
index pregnancy and appear to benefit from either lifestyle or
pharmacologic interventions.
Acknowledgments
The investigators gratefully acknowledge the commitment and dedica-
tion of the participants of the DPP. The National Institute of Diabetes
and Digestive and Kidney Diseases (NIDDK) of the National Institutes
of Health provided funding to the clinical centers and the coordinating
center for the design and conduct of the study and the collection, man-
agement, analysis, and interpretation of the data. The Southwestern
American Indian Centers were supported directly by the NIDDK and the
Indian Health Service. The General Clinical Research Center Program,
National Center for Research Resources, supported data collection at
many of the clinical centers. Funding for data collection and participant
support was also provided by the Office of Research on Minority Health,
the National Institute of Child Health and Human Development, the
National Institute on Aging, the Centers for Disease Control and Pre-
vention, and the American Diabetes Association. Bristol-Myers Squibb
and Parke-Davis provided medication. This research was also supported,
in part, by the intramural research program of the NIDDK. LifeScan
Inc., Health O Meter, Hoechst Marion Roussel, Inc., Merck-Medco
Managed Care, Inc., Merck and Co., Nike Sports Marketing, Slim
Fast Foods Co., and Quaker Oats Co. donated materials, equipment,
or medicines for concomitant conditions. McKesson BioServices
Corp., Matthews Media Group, Inc., and the Henry M. Jackson Foun-
dation provided support services under subcontract with the coordi-
nating center. The opinions expressed are those of the investigators
and do not necessarily reflect the views of the Indian Health Service
or other funding agencies. A complete list of centers, investigators,
and staff can be found elsewhere (5). Members of the DPP Research
Group are listed elsewhere (5).
Address all correspondence and requests for reprints to: Diabetes
Prevention Program Coordinating Center, The Biostatistics Center,
George Washington University, 6110 Executive Boulevard, Suite 750,
Rockville, Maryland 20852. E-mail: dppmail@biostat.bsc.gwu.edu.
Disclosure Statement: The authors have nothing to disclose.
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TABLE 2. Effect of DPP treatment on incidence of diabetes
Placebo Metformin ILS
GDM
(n ⴝ122)
No GDM
(n ⴝ487)
GDM
(n ⴝ111)
No GDM
(n ⴝ464)
GDM
(n ⴝ117)
No GDM
(n ⴝ465)
Incidence of diabetes (number of cases per 100
person-years)
a
15.2
b
8.9 7.8 7.8 7.4 4.7
Reduction in incidence (compared with placebo)
a
50.4
c
14.4 53.4
c
49.2
c
Number needed to treat (to prevent one case in
3 yr compared with placebo)
a
6.1 24.0 5.3 9.0
a
Adjusted for age.
b
P⬍0.05 compared with non-GDM group.
c
P⬍0.05 compared with placebo.
J Clin Endocrinol Metab, December 2008, 93(12):4774 – 4779 jcem.endojournals.org 4779
