To compare carbohydrate metabolism, adrenal and thyroid function during use of a combined contraceptive vaginal ring (NuvaRing, NV Organon, Oss, The Netherlands) with those of a combined oral contraceptive.

Healthy women aged 18-40 years used either the vaginal ring, delivering 15 microg ethinylestradiol and 120 microg of etonogestrel per day, or a combined oral contraceptive containing 30 microg ethinylestradiol and 150 microg levonorgestrel, for six cycles. Each cycle comprised 3 weeks of use of the ring or the pill followed by 1 ring- or pill-free week. The following parameters were measured at baseline and at the end of cycles 3 and 6: carbohydrate metabolism (glucose, insulin, glycosylated hemoglobin); adrenal function (total cortisol, cortisol binding globulin, dehydroepiandrosterone sulfate); thyroid function (thyroid stimulating hormone, free thyroxine).

Small and similar increases in insulin were seen in both groups. Concentrations of cortisol binding globulin and total cortisol rose significantly less during ring use than during combined oral contraceptive use (cycle 3, p= 0.0002; cycle 6, p < 0.0001). Levels of dehydroepiandrosterone sulfate did not change in either group. Thyroid stimulating hormone levels increased significantly more in the ring group at cycle 3 (p = 0.0016) but free thyroxine levels were unchanged in both groups.

Both the vaginal ring and the oral contraceptive have no clinically relevant effects on carbohydrate metabolism, adrenal or thyroid function.