Mediating effect of vascular risk factors underlying the link between gestational diabetes and cardiovascular disease

Background — Women with gestational diabetes (GDM) have an elevated lifetime incidence of cardiovascular disease (CVD), but the basis of this excess risk remains to be established. In this context, we hypothesized that chronic exposure to adverse cardiovascular risk factors may contribute to their elevated risk of CVD. We thus sought to quantify the determinants of CVD risk in women with a history of GDM by performing mediation analyses.

Methods — Women in Ontario, Canada, with a live-birth pregnancy between Jan 1998 and Dec 2017 (n=757,541) were followed for a median of 13.2 years and stratified into the following 4 groups: women with GDM who developed CVD (GDM+/CVD+); women without GDM who developed CVD (GDM−/CVD+); those with GDM but no CVD (GDM+/CVD−); and those with neither GDM nor CVD (GDM−/CVD−). Lipids (total cholesterol, LDL, HDL, triglycerides) and glycemic variables (A1c, fasting glucose) were measured between 4.3±3.0 and 4.8±3.4 times over follow-up.

Results — On successive measurements at a median of 4.8, 7.1, and 8.7 years postpartum, respectively, each lipid and glycemic measure progressively worsened from GDM−/CVD− to GDM+/CVD− to GDM−/CVD+ to GDM+/CVD+ (all p<0.0001). At each point in time, each of the lipid and glycemic measures was significantly worse in GDM+/CVD+ compared to GDM+/CVD− (all p<0.001). Moreover, among women who did not develop CVD, all lipid and glycemic measures were significantly worse in those with previous GDM (all p<0.001 for GDM+/CVD− vs GDM−/CVD−). Mediation analyses revealed that the dominant determinants of CVD risk in women with GDM were A1c (56.0% mediation, 95%CI 47.4–67.8) and fasting glucose (47.4%, 38.8–60.8), followed by HDL (25.2%, 21.3–30.7) and triglycerides (12.1%, 9.7–15.6). Upon exclusion of those who developed diabetes during follow-up, the key determinants were HDL (40.8%), fasting glucose (37.7%), A1c (28.6%), triglycerides (21.0%), and LDL (9.9%).

Conclusions — Adverse glycemic and lipid measures mediate the elevated risk of CVD in women with previous GDM, with the impact of lipids particularly evident in those who do not develop diabetes. These findings thus identify potential targets for risk factor monitoring and ultimately early intervention towards the goal of primary prevention of CVD in this at-risk patient population.