Miscarriage

Hello, I recently had a miscarriage at 7 weeks about three weeks ago.  During the u/s the doctors found a 7cm dermoid.  Could that have caused my miscarriage?  I've never had trouble getting/staying pregnant in the past and have had two healthy pregnancies.  We want to try again soon, as my doctor suggested monitoring it.  Is this a wise choice or do I risk another miscarriage leaving it in?