Gestational Diabetes Mellitus and Risk of Selected Cancers: A Danish National Register-based Cohort Study

CONTEXT: Gestational diabetes mellitus (GDM) is the most common medical complication of pregnancy and is associated with type 2 diabetes, which is associated with breast cancer and kidney cancer. However, little is known about the risk of cancer following a GDM diagnosis. OBJECTIVE: This study aimed to test the hypothesis that a history of GDM associates with increased risk of breast, gynecological, thyroid, and kidney cancer. METHODS: National cohort study, based on Danish registry data. The study population included a group of women exposed to GDM in their pregnancy leading to delivery between 2000 and 2019 or 1978 and 1997 and a 1:10 matched nonexposed group, matched on calendar period of delivery, the woman´s age (birth year), and the woman´s registered region of residence at delivery. Poisson regression adjusting for educational level was conducted. RESULTS: Of the 314 742 deliveries included, 28 613 deliveries were in the exposed group and 286 129 in the nonexposed. The median follow-up time was 8.1 years. We found no increased risk of the selected cancers combined [adjusted incidence rate ratio (aIRR) 1.05; 95% confidence interval (CI), 0.94-1.18], breast cancer (aIRR 1.02; 95% CI, 0.89-1.17), gynecological cancer (aIRR 1.00; 95% CI, 0.79-1.26), or thyroid cancer (aIRR 1.26; 95% CI, 0.86-1.82). However, an increased risk of kidney cancer was seen in women with previous GDM compared with women without GDM (aIRR 1.92; 95% CI, 1.10-3.33), although it was a very small absolute risk. CONCLUSION: No elevated risk was found for the selected cancers combined. Women with previous GDM had an increased risk of kidney cancer, a rare cancer form.