OBJECTIVE:

The purpose of this study was to assess changes in the prevalence of preexisting diabetes (diabetes antedating pregnancy) and gestational diabetes mellitus (GDM) from 1999 through 2005.

RESEARCH DESIGN AND METHODS:

In this retrospective study of 175,249 women aged 13-58 years with 209,287 singleton deliveries of >or=20 weeks' gestation from 1999 through 2005 in all Kaiser Permanente hospitals in southern California, information from clinical databases and birth certificates was used to estimate the prevalence of preexisting diabetes and GDM.

RESULTS:

Preexisting diabetes was identified in 2,784 (1.3%) of all pregnancies, rising from an age- and race/ethnicity-adjusted prevalence of 0.81 per 100 in 1999 to 1.82 per 100 in 2005 (P(trend) < 0.001). Significant increases were observed in all age-groups and all racial/ethnic groups. After women with preexisting diabetes were excluded, GDM was identified in 15,121 (7.6%) of 199,298 screened pregnancies. The age- and race/ethnicity-adjusted GDM prevalence remained constant at 7.5 per 100 in 1999 to 7.4 per 100 in 2005 (P(trend) = 0.07). Among all deliveries to women with either form of diabetes, 10% were due to preexisting diabetes in 1999, rising to 21% in 2005, with GDM accounting for the remainder.

CONCLUSIONS:

The stable prevalence of GDM and increase in the prevalence of preexisting diabetes were independent of changes in the age and race/ethnicity of the population. The increase in preexisting diabetes, particularly among younger women early in their reproductive years, is of concern.