Women with type 1 diabetes require safe and effective contraception for several reasons. Pregnancy may accelerate the progression of diabetes and have significant short- and long-term implications for the mother. Pregnancy in patients with type 1 diabetes should be planned, because optimal glycemic control at conception and during early pregnancy reduces the incidence of congenital abnormalities and fetal growth problems. However, potential vascular and metabolic concerns limit contraceptive options for women with diabetes. Copper intrauterine devices (IUDs) are a safe and well-tolerated contraceptive option for many women with diabetes, but the suitability of levonorgestrel-releasing IUDs (Mirena) has not been established. Some experts are concerned that levonorgestrel could adversely affect carbohydrate and lipid metabolism. Rogovskaya and colleagues compared the effect of progestin-containing and copper IUDs on glucose metabolism in women with uncomplicated insulin-dependent type 1 diabetes.

The randomized controlled trial included women 18 to 45 years of age who had well-controlled insulin-dependent type 1 diabetes. Participants were required to have normal glucose and A1C levels and no evidence of retinopathy or nephropathy. After a comprehensive evaluation, participants were randomly assigned to receive a copper IUD or a levonorgestrel-releasing IUD. Patients were assessed and A1C levels were measured at six weeks, six months, and one year.

The 31 women assigned to each group were comparable in all significant variables. The average age was 33 years, and the average participant weighed approximately 132 lb (60 kg). The average duration of diabetes was more than six years, and the average participant had been pregnant more than twice and had had at least one delivery.

The progestin-containing IUD did not affect A1C levels, fasting glucose levels, or daily insulin requirements over one year compared with the copper IUD. The continuation rates were 86.7 percent for the levonorgestrel-releasing IUD and 90.3 percent for the copper IUD, but these rates were not statistically different.

The authors conclude that women using levonorgestrel-releasing IUDs do not have significant changes in A1C levels, daily insulin requirements, or average fasting blood glucose levels after 12 months of use. The mild changes in glycemic control with the progestin-containing IUD were identical to those in women using a copper-containing device and probably were not clinically significant. Both devices are reliable contraceptive options for women with diabetes, and the levonorgestrel-containing device may decrease menstrual blood loss and dysmenorrhea.