This is a randomized controlled trial to assess the effect of a levonorgesterel-releasing intrauterine device (LNG IUD, Mirena®) versus a copper IUD (Paraguard®) on coagulation parameters known to be associated with risk of thrombosis (blood clots). Both the LNG IUD and the copper IUD are FDA approved devices for contraception.

Women enrolled in this study will be randomized to receive either the LNG IUD or the copper IUD. They will complete a one month bleeding diary prior to insertion of the IUD and again for one month while the IUD is in place. They will undergo phlebotomy (blood draw) at baseline (prior to insertion of the IUD), two and four months. Stored samples will be used to measure D-dimer, C-reactive protein (CRP), antithrombin (AT), factor VIIIc, activated partial thromboplastin time (aPTT) and activated partial thromboplastin time plus activated protein C (aPTT + APC). Both groups will undergo a GYN exam with screening for bacterial vaginosis and gonorrhea/chlamydia cultures prior to insertion of the IUD. A brief survey to assess the women's experience with the IUD, including symptomatology and satisfaction with the device, will be conducted at the four months after insertion.

Inclusion Criteria:

• Women who desire long-term, reversible contraception

Exclusion Criteria:

• Women with coagulopathies
• History of thrombotic events
• Pregnancy
• Active pelvic infection
• Known hypersensitivity to progestin
• Undiagnosed vaginal bleeding
• Wilson's disease
• Sensitivity to copper
• Uterine anatomy that precludes insertion of an IUD
• Women with multiple sexual partners and history within the last 5 years of alcoholism or drug abuse.
• Additionally, women must be greater than 3 months postpartum and have had two months without oral contraceptive pills or 6 months without Depo Provera prior to enrollment.