Gestational Diabetes Risk in Migrants. A Nationwide, Register-Based Study of all Births in Denmark 2004 to 2015

BACKGROUND: Much remains to be understood about socioeconomic position and body mass index (BMI) in the pathways linking ethnicity, migration, and gestational diabetes mellitus (GDM). We investigated differences in GDM prevalence according to maternal country of origin and the role played by socioeconomic position and BMI on this relationship. Finally, we examined how length of residency was associated with GDM.

METHODS: A register-based cohort study of the 725 482 pregnancies that resulted in a birth in Denmark, 2004 to 2015. Of these, 14.4% were by women who had migrated to Denmark. A GDM diagnosis was registered in 19 386 (2.7%) pregnancies, of which 4464 (23.0%) were in immigrant women. The crude risk of GDM according to maternal country of origin compared to Danish-born women ranged from an odds ratio (OR) of 0.50 (95% CI 0.34-0.71) for women from Sweden to an OR of 5.11 (95% CI 4.28-6.11) for women from Sri Lanka. Adjustment for socioeconomic position slightly attenuated the risks. Adjusting for BMI resulted in increased ORs for women, especially from Asian countries. The separate and joint effects of migration and overweight on GDM risk differed substantially between the countries of origin (P value interaction term < .001). Immigrants with 10 or more years of residency had a 56% increased risk of GDM (OR 1.56, 95% CI 1.44-1.68) compared to immigrants with less than 5 years in Denmark. This risk was somewhat diluted when adjusting for age and BMI.

CONCLUSIONS: This study demonstrates substantial variation in the risk of GDM according to country of origin. The risk associations are only slightly affected by socioeconomic position and BMI.