Based on a quick research I did in Google, it appears that prednisone does not affect oral contraception, so you should still be protected from pregnancy. However, remember that oral contraception does not protect you from STDs, so depending on your situation, you may want to double up with a condom. The answer I found said that oral contraception may increase the effectiveness of prednisone and you should therefore discuss the issue with your rheumatologist as they may want to lower the dose. Whenever you get prescribed a new medication by a doctor, be sure to tell them what other medications you're taking so they can avoid giving your medication that might potentially interact with another drug.