• Jantien Visser, Marieke Snel, and Huib A A M Van Vliet.
• Department of Obstetrics and Gynaecology, Leiden University Medical Center, Leiden, Netherlands. jantienvisser@gmail.com.
• Cochrane Db Syst Rev. 2013 Mar 28; 2013 (3): CD003990CD003990.

BackgroundAdequate contraceptive advice is important in both women with diabetes mellitus type 1 and type 2 to reduce the risk of maternal and infant morbidity and mortality in unplanned pregnancies. A wide variety of contraceptives are available for these women. However, hormonal contraceptives might influence carbohydrate and lipid metabolism and increase micro- and macrovascular complications, so caution in selecting a contraceptive method is required.ObjectivesTo investigate whether progestogen-only, combined estrogen and progestogen or non-hormonal contraceptives differ in terms of effectiveness in preventing pregnancy, in their side effects on carbohydrate and lipid metabolism, and in long-term complications such as micro- and macrovascular disease when used in women with diabetes mellitus.Search MethodsThe search was performed in CENTRAL, MEDLINE, EMBASE, POPLINE, CINAHL, WorldCat, ECO, ArticleFirst, the Science Citation Index, the British Library Inside, and reference lists of relevant articles. The last search was performed in January 2013. In addition, experts in the field and pharmaceutical companies marketing contraceptives were contacted to identify published, unpublished or ongoing studies.Selection CriteriaRandomised and quasi-randomised controlled trials that studied women with diabetes mellitus comparing: 1. hormonal versus non-hormonal contraceptives; 2. progestogen-only versus estrogen and progestogen contraceptives; 3. contraceptives containing < 50 µg estrogen versus contraceptives containing ≥ 50 µg estrogen; and 4. contraceptives containing first-, second- and third-generation progestogens, drospirenone and cyproterone acetate. The principal outcomes were contraceptive effectiveness, diabetes control, lipid metabolism and micro- and macrovascular complications.Data Collection And AnalysisTwo investigators evaluated the titles and abstracts identified from the literature search. Quality assessment was performed independently with discrepancies resolved by discussion or consulting a third review author. Because the trials differed in studied contraceptives, participant characteristics and methodological quality, we could not combine the data in a meta-analysis. The trials were therefore examined on an individual basis and narrative summaries were provided.Main ResultsFour randomised controlled trials were included. No unintended pregnancies were reported during the study periods. Only one trial was of good methodological quality. It compared the influence of a levonorgestrel-releasing intrauterine device (IUD) versus a copper IUD on carbohydrate metabolism in women with type 1 diabetes mellitus. No significant difference was found between the two groups. The other three trials were of limited methodological quality. Two compared progestogen-only pills with different estrogen and progestogen combinations, and one also included the levonorgestrel-releasing IUD and copper IUD. The trials reported that blood glucose levels remained stable during treatment with most regimens. Only high-dose combined oral contraceptives and 30 µg ethinylestradiol + 75 µg gestodene were identified as slightly impairing glucose homeostasis. The three 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 oral contraceptives also slightly improved lipid metabolism and no influence was seen while using the levonorgestel-releasing IUD. Only one study reported on micro- and macrovascular complications. It observed no signs or symptoms of thromboembolic incidents or visual disturbances, however study duration was short. Only minor adverse effects were reported in two studies.Authors' ConclusionsThe four included randomised controlled trials in this systematic review provided insufficient evidence to assess whether progestogen-only and combined contraceptives differ from non-hormonal contraceptives in diabetes control, lipid metabolism and complications. Three of the four studies were of limited methodological quality, sponsored by pharmaceutical companies and described surrogate outcomes. Ideally, an adequately reported, high-quality randomised controlled trial analysing both intermediate outcomes (that is glucose and lipid metabolism) and true clinical endpoints (micro- and macrovascular disease) in users of combined, progestogen-only and non-hormonal contraceptives should be conducted. However, due to the low incidence of micro- and macrovascular disease and accordingly the large sample size and long follow-up period needed to observe differences in risk, a randomised controlled trial might not be the ideal design.

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