OBJECTIVE: Women with gestational diabetes mellitus (GDM) and their offspring are at increased risk of deve-loping diabetes. Although increases in diabetes prevalence have been reported in the United States, it is unknown, whether this trend is also occurring for GDM. We examined trends in the yearly cumulative incidence of GDM between the years 1991 and 2000. METHODS: A cohort study of 267,051 pregnancies screened for GDM that occurred among members of the Northern California Kaiser Permanente Medical Care Program, representing 86.8%of all eligible pregnancies, was undertaken. RESULTS: GDM was identified in 14,175 pregnancies according to the diagnostic plasma glucose thresholds of the American Dia betes Association (96.5%) or the World Health Organization (3.5%). An additional 2,743 pregnant women with GDM were identified by a hospital discharge diagnosis. The women screened in 2000 were slightly older (mean [standard deviation] age 28.8 [6.0] years) than were those screened in 1991 (28.2 [5.7] years) and more likely to be front minority ethnic groups (51.4%versus 37.3%identified as African American, Asian, Hispanic, and other). The age-and ethnicity-adjusted yearly cumulative incidence of GDM increased steadily from 5.1%in 1991 to 7.4%in 1997 and leveled off through 2000 (6.9%). DISCUSSION: The observed increase in yearly cumulative incidence of GDM was independent of changes in age and ethnicity of the study population. A true increase in GDM incidence might reflect or contribute to the increases in the prevalence of diabetes and obesity. Coordinated efforts are needed to alter this trend and to prevent chronic diabetes in GDM patients and their offspring. OBJECTIVE: Women with gestational diabetes mellitus (GDM) and their offspring are at increased risk of deve-loping diabetes. Although increases in Pest prevalence have been reported in the United States, it is unknown, whether this trend is also occurring for GDM. We examined trends in the cumulative rate of the GDM between the years 1991 and 2000. METHODS: A cohort study of 267,051 pregnancies screened for GDM that occurred among members of the Northern California Kaiser Permanente Medical Care Program, representing 86.8% of all eligible pregnancies, was undertaken. RESULTS: GDM was identified in 14,175 pregnancies according to the diagnostic plasma glucose thresholds of the American Diabetes Association (96.5%) or the World Health Organization (3.5%). An additional 2,743 pregnant women with GDM were identified by a hospital discharge The women screened in 2000 were slightly older (mean [standard deviation] age 28.8 [6.0] years) than those those screened in 1991 (28.2 [5.7] years) and more likely to be front minority ethnic groups (51.4% versus 37.3% identified as African American, Asian, Hispanic, and other). The age-and ethnicity-regulatoryatch cumulative positive cumulative incidence of GDM increased steadily from 5.1% in 1991 to 7.4% in 1997 and leveled off through 2000 (6.9%). DISCUSSION: The observed increase in cumulative cumulative incidence of GDM was independent of changes in age and ethnicity of the study population. A true increase in GDM may might reflect or contribute to the increases in the prevalence of diabetes and obesity. Coordinated efforts are needed to alter this trend and to prevent chronic diabetes in GDM patients and their offspring.