Recent data show that gestational diabetes mellitus (GDM) prevalence has increased by ~10–100% in several race/ethnicity groups during the past 20 years. A true increase in the prevalence of GDM, aside from its adverse consequences for infants in the newborn period, might also reflect or contribute to the current patterns of increasing diabetes and obesity, especially in the offspring. Therefore, the public health aspects of increasing GDM need more attention.

The frequency of GDM usually reflects the frequency of type 2 diabetes in the underlying population. Established risk factors for GDM are advanced maternal age, obesity, and family history of diabetes. Unquestionably, there are ethnic differences in the prevalence of GDM. In the U.S., Native Americans, Asians, Hispanics, and African-American women are at higher risk for GDM than non-Hispanic white women. In Australia, GDM prevalence was found to be higher in women whose country of birth was China or India than in women whose country of birth was in Europe or Northern Africa.

GDM prevalence was also higher in Aboriginal women than in non-Aboriginal women. In Europe, GDM has been found to be more common among Asian women than among European women. The proportion of pregnancies complicated by GDM in Asian countries has been reported to be lower than the proportion observed in Asian women living in other continents. In India, GDM has been found to be more common in women living in urban areas than in women living in rural areas.

The trend toward older maternal age , the epidemic of obesity and diabetes , and the decrease in physical activity and the adoption of modern lifestyles in developing countries may all contribute to an increase in the prevalence of GDM. Because GDM is associated with several perinatal complications, and because women with GDM and their offspring are also at increased risk of developing diabetes later in life, it is critical to assess trends in GDM prevalence to allocate appropriate resources to perinatal management and postpartum diabetes prevention strategies.

Characterizing trends in GDM might also help to understand possible mechanisms for the increase of obesity and type 2 diabetes, especially in children. Recent data show that GDM prevalence has increased by ~16–127% in several race/ethnicity groups during the past 20 years. These variations may depend on differences in methodology and study populations across studies. Methodological issues are described below as well as studies of trends in GDM.

Some studies calculated the “cumulative incidence” (defined as the percentage of pregnancies in which GDM was recognized) because GDM frequency was calculated among screened pregnancies regardless of whether they delivered an infant. However, most of the studies identified only women who delivered, and therefore they calculated the “prevalence” of GDM at delivery. For simplicity, the term “prevalence” of GDM will be used for all studies, since the GDM cumulative incidence estimates are similar to the prevalence estimates, given the small number of preggnancies that were screened but did not deliver an infant.

WHY IS GDM INCREASING?

All six studies of trend in GDM conducted in different populations and with different methodologies consistently reported an increase in GDM in all race/ethnicity groups, suggesting that the observed increase in GDM prevalence may be true. However, none of the six studies could distinguish between women who have been reclassified postpartum as having underlying diabetes from those who returned to normal glucose tolerance. Higher relative increases in younger women suggest that the prevalence of risk factors for GDM may have increased more in younger women than in older women. However, none of the studies had information on maternal obesity, the most important modifiable risk factor for GDM , and therefore none of the studies was able to assess whether the observed increases in GDM prevalence were explained by concomitant increases in maternal obesity.

It is worth noting some results that might suggest a possible plateau in the increase of GDM prevalence. The Northern California Kaiser Permanente study showed that the increase in GDM prevalence leveled off after 1997. Although women who were born more recently had a higher prevalence of GDM than women who were born later, no differences in the prevalence of GDM between the two most recent birth cohorts were observed. The lack of data on maternal obesity make it impossible to explain whether these findings would be explained by a plateau of maternal obesity after 1997, or whether maternal obesity has increased less in the younger generations, or whether the increasing prevalence of GDM in women from younger birth cohorts is independent of the effect of obesity.

In summary, there is a need for large epidemiological studies that assess prepregnancy and/or postpartum glucose tolerance status to evaluate the contribution of underlying glucose intolerance in the development of GDM. There is also the need of additional studies that assess prepregnancy obesity and possible GDM risk factors operating before childbearing to better understand trends in the prevalence of GDM and plan prevention strategies. The higher prevalence of GDM among Asian women needs further investigation.

Epidemiological data on modifiable risk factors of GDM are sparse. Besides obesity, a major GDM risk factor, there is a suggestion that physical inactivity , diets high in saturated fat , and smoking are associated with increasing risk for GDM or recurrent GDM. It is critical to know the risk factors for GDM not only to better understand trends in GDM, but also to allow early identification of women at risk and prevention of this common pregnancy complication.

Assiamira Ferrara, MD, PHD

From the Division of Research, Kaiser Permanente Medical Care Program of Northern California, Oakland, California

Address correspondence and reprint requests to Assiamira Ferrara, Division of Research, Kaiser Permanente Medical Care Program of Northern California, 2000 Broadway, Oakland, CA 94612. E-mail: .(JavaScript must be enabled to view this email address)

Abbreviations: GDM, gestational diabetes mellitus

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