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 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 2000-2019 or 1978-1997, and a 1:10 matched non-exposed 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, 286,129 in the non-exposed. 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% 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 a very small absolute risk.

[CONCLUSIONS] 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.