In this study, we review studies published in the past 10 years that examine the prevalence and trends in the prevalence of GDM. In summary, the prevalence of GDM in a population is reflective of the prevalence of type 2 diabetes in that population; therefore, ethnic and racial populations with a high prevalence of type 2 diabetes are at higher risk of GDM. In low-risk populations such as those found in Sweden the prevalence in population-based studies is lower than 2% even when universal testing is offered (71
), while studies in high-risk populations such as the Native American Cree, Northern Californian Hispanics and Northern Californian Asians reported prevalence rates based on NDDG diagnostic criteria following universal screening ranging from 4.9% to 12.8%(61
). Prevalence rates for GDM obtained from hospital-based studies similarly reflect the risk of type 2 diabetes in a population. A single hospital-based study in Australia using ADIPS diagnostic criteria and universal screening reports prevalences ranging from 3.0% in Anglo-Celtic women to 17.0% in Indian women(102
). Finally, of the eight studies published in the past 10 years that report on trends in the prevalence of GDM(104
), one study reports a significant decline in the prevalence of GDM(110
), one study reports no significant change in the prevalence of GDM(108
), and 6 studies report an increase in the prevalence of GDM across most racial/ethnic groups studied(104
A number of factors influence the prevalence of GDM identified in a population and make it difficult to compare prevalences across populations. In the United States the definition of GDM and screening policies concerning GDM have changed considerably in the past 20 years and still vary substantially. Despite four international conferences aimed at developing a consensus definition for GDM worldwide, the definition and screening criteria for GDM continue to vary, making it difficult to compare prevalences between countries. A critical change in the definition of GDM occurred at the 4th
International Workshop conference on GDM in 1997, endorsed by the ADA, when it was largely agreed that the C & C criteria should replace the NDDG criteria, significantly lowering the accepted cutpoints and therefore raising the prevalence of GDM(58
). Finally, because GDM encompasses undiagnosed type 2 diabetes prior to pregnancy, the definition, screening strategies and awareness of type 2 diabetes in a population ultimately influences the observed prevalence of GDM in a population. This is of particular importance during the past decade because the diagnostic criteria for diabetes and recommended screening practices have changed in the United States and internationally, namely the threshold for a fasting glucose level diagnostic of diabetes was lowered from 140 mg/dL to 126 mg/dL(112
In addition to the varied definitions and screening policies for GDM and diabetes there are a number of factors which make it difficult to compare GDM prevalence rates across populations and over time. Increased maternal age at delivery is a strong risk factor for GDM. Hence, a contributing factor to increased prevalence rates of GDM in a given population over time, or differences observed between populations, is increased maternal age at delivery. Because we are unable to age standardize our prevalence rates across studies, we are unable to determine the impact of maternal age at delivery on prevalence rates across studies. However, increasing maternal age at delivery is one factor likely influencing the increasing prevalence of GDM in developed countries. Maternal age at delivery is also likely to vary and affect prevalence differences when comparing developed and undeveloped countries. Because the prevalence of GDM in a population reflects the prevalence of type 2 diabetes in a population, and certain racial and ethnic groups are at increased risk of type 2 diabetes, a second factor which may influence changes in prevalence overtime in a given population is a change in the racial/ethnic composition of that population. While racial/ethnic group specific prevalences of GDM reflect the prevalence within a specific segment of the population, they may fail to reflect the broader public health impact of GDM as the overall population prevalence increases.
Changes in lifestyle including decreased physical activity and increased caloric consumption continue to fuel the obesity epidemic. Obesity, often accompanied by insulin resistance, is a strong risk factor for GDM and likely contributes to the increasing prevalence of GDM. The National Longitudinal Survey of Youth, a prospective cohort study of children aged 4 to 12 years carried out between 1986 and 1998 in the United States, indicated that the prevalence of overweight children increased significantly and steadily throughout the study(114
). By the end of the study in 1998, obesity affected an estimated 21.5% of African American children, 21.8% of Hispanic children and 12.3% of non-Hispanic white children(114
). In the 2003–2004 NHANES, 17.1% of individuals ages 2 to 19 years were overweight; more than triple the percent in 1980(115
). In adults of childbearing age the prevalence of obesity also continues to rise; in 18- to 29-year olds the prevalence of obesity rose from 7.1% in 1991 to 12.1% in 1998 in the Behavioral Risk Factor Surveillance System survey (116
As obesity and diabetes increasingly affect young adults and women of childbearing age, understanding the public health impact of diabetes during pregnancy and its affect on infant health becomes important. Exposure to maternal diabetes later in pregnancy is associated with high birth weight, increased childhood and adult obesity and increased risk of type 2 diabetes (42
); therefore, the diabetic intrauterine environment may not only be a result of the obesity and diabetes epidemics, it may be partially responsible and currently fueling the epidemics. Moreover, because both obesity and diabetes disproportionately affect minority women including minority women of childbearing age(8
), if the intrauterine environment is contributing to the epidemics, it perpetuates and widens health disparities between racial and ethnic groups.
The population health impact of GDM is not limited to exposed offspring, but affects maternal health as well. Once diagnosed with GDM, a woman has a substantial chance of developing type 2 diabetes following delivery, with some studies reporting a 5 year cumulative incidence rate of over 50%(122
). Moreover, because childbearing women are relatively young, women with GDM who develop overt diabetes acquire it at a young age, substantially increasing their lifetime risk of developing complications from diabetes. The Diabetes Prevention Program was one of several clinical trials which indicates that either through diet and exercise, or with the aid of a pharmacological agent, it is possible to lower the incidence or delay the onset of diabetes among individuals at high risk of the disease(123
). Women with GDM, because of their high diabetes risk and young age, are ideally suited to be targeted for lifestyle or pharmacological interventions to delay or prevent the onset of overt diabetes(123
). Moreover, because women with GDM are of childbearing age, preventing or delaying the onset of overt diabetes not only improves the woman’s health, but protects future offspring from the harmful effects of elevated glucose levels in pregnancy(127
In summary, diabetes during pregnancy is a common and increasing complication of pregnancy that differentially affects racial and ethnic minority populations dependent upon their underlying risk of diabetes. Hence, an important public health priority, consistent with reducing health disparities between racial and ethnic groups, is prevention of diabetes, starting with maternal health pre- and post-conception.