Prevalence and regional differences of gestational diabetes mellitus and oral glucose tolerance tests in Finland

Background: The prevalence of gestational diabetes (GDM) is constantly increasing all around the world. Aim of this study is to report prevalence and regional differences of GDM, oral glucose tolerance tests (OGTT) and register-based GDM risk factors [age and body mass index (BMI)] among Finnish women. Methods: Data from the Finnish Medical Birth Register including all deliveries in Finland during 2004-06 (N = 174 634) were used. The criteria for GDM were abnormal results in OGTT, GDM diagnosis based on ICD-10 classification or use of insulin treatment during pregnancy. Pregnant women with type I diabetes were excluded, but women with pregestational diabetes (type II) were included since they also can receive GDM diagnosis. Results: The prevalence of GDM was 10-11% and OGTTs 22-28% between the period 2004 until 2006. Regional differences were 2-fold both in prevalence of GDM (8-15%) and OGTTs (19-34%). Proportions of obese women varied between 28% and 35% and women aged > 40 years between 3% and 4%. The regional differences in GDM prevalence were not attenuated when risk factors were taken into account. Overweight and age epsilon years explained only a fourth of the variation in GDM prevalence. Conclusion: Proportion of women undergoing OGTT increased but the prevalence of GDM did not during the study period. Two-fold regional differences in OGTT prevalence explained higher proportion of variation in prevalence of GDM than risk factors available from birth registry, age and BMI.