- Objective: To investigate whether patients with a history of gestational diabetes mellitus (GDM) have an increased future risk for female malignancies. Study design: A population-based study compared the incidence of long-term female malignancies (ovary, uterine, breast, and uterine cervix) in a cohort of women with and without a diagnosis of GDM. Deliveries occurred between the years 1988-2013, with a mean follow-up duration of 12 years. Women with known malignancies prior to the index pregnancy were excluded. Kaplan-Meier survival curve was used to estimate cumulative incidence of malignancies. Cox proportional hazards models were used to estimate the adjusted hazard ratios (HR) for female malignancy. Results: During the study period, 1,04,715 deliveries met the inclusion criteria; 9.4% (n = 9893) occurred in patients with a history of GDM in at least one of their pregnancies. During the follow-up period, patients with GDM had a significantly increased risk of being diagnosed with female malignancies, including ovarian, uterine, and breast cancer. Using a Kaplan-Meier survival curve, patients with a previous diagnosis of GDM had a significantly higher cumulative incidence of female malignancies. Using a Cox proportional hazards model, adjusted for confounders, such as parity, maternal age, and fertility treatments, a history of GDM remained independently associated with female malignancies (adjusted HR, 1.3; 95% CI 1.2-1.6; P = 0.001). Conclusion: Patients with a history of GDM have an increased risk for future breast, ovarian, and uterine malignancies.