A Cochrane review [Abstract] 1 included 4 studies with a total of 227 subjects. The only good quality trial compared levonorgestrel-releasing IUD versus copper-IUD (n=62). No difference was found in daily insulin requirement, glycosylated hemoglobin (HbA1c) or fasting blood sugar after twelve months in women with type 1 DM. 2 trials compared progestogen-only pills with different estrogen/progestogen combinations (n=52) and one (n=113) also included the levonorgestrel-releasing IUD and copper IUD. Blood glucose levels remained stable during treatment with most regimens. Only high-dose combined oral contraceptives and 30 µg ethinylestradiol + 75 µg gestodene were found to slightly impair glucose homeostasis. The 3 studies found conflicting results regarding lipid metabolism. Some combined oral contraceptives appeared to have a minor adverse effect while others appeared to slightly improve lipid metabolism. The copper-IUD and progestogen-only contraceptives also slightly improved lipid-metabolism and no influence was seen while using levonorgestel-releasing IUD. Only one study reported on micro- and macrovascular complications. No signs or symptoms of thromboembolic incidents or visual disturbances were observed, but study duration was short. Only minor adverse effects were reported in 2 studies. Unintended pregnancies were not observed during any of the studies.
Comment: The quality of evidence is downgraded by study quality (unclear allocation concealment and blinding), by inconsistency (variability in results across studies), by imprecise results (limited study size for each comparison), and by potential reporting bias (small trials sponsored by pharmaceutical companies).
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